Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Come on, folks. never hook anything directly to the power line. The source is just too stiff. Use an opto. I used fiber optic isolation with my big DC power supply. Don I used to agree, until actually tried it myself. Now this is how I do my picPET 60 Hz data logging: Dangerous.. A single component failure puts you hot to the line, without current limiting. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
David VanHorn wrote: Come on, folks. never hook anything directly to the power line. The source is just too stiff. Use an opto. I used fiber optic isolation with my big DC power supply. Don I used to agree, until actually tried it myself. Now this is how I do my picPET 60 Hz data logging: Dangerous.. A single component failure puts you hot to the line, without current limiting. If that bothers you, don't use unfused 1M resistors, use a fuse and pairs of 500K resistors in series. That way it takes a double component failure... And if that still bothers you, use triple 330K... Or add a pair of safety rated series capacitors. Even a common lamp cord is only a single component failure away from being hazardous. Somewhere or another there should be a compromise that makes you happy... you will, however, never achieve true safety as long as you are alive. -Chuck Harris ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Somewhere or another there should be a compromise that makes you happy... you will, however, never achieve true safety as long as you are alive. I am far more aware of this than you might suspect, but I do think that it is a very good idea to know the risks involved. An optoisolator is vanishingly unlikely to fail shorted, in that they are specifically designed with this failure mode in mind. A resistor is likely to fail open, but failing shorted isn't unheard of. See also designs for wrist straps. I won't be trusting a single resistor to sit between me and a fire that could kill people. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
David VanHorn wrote: Somewhere or another there should be a compromise that makes you happy... you will, however, never achieve true safety as long as you are alive. I am far more aware of this than you might suspect, but I do think that it is a very good idea to know the risks involved. An optoisolator is vanishingly unlikely to fail shorted, in that they are specifically designed with this failure mode in mind. A resistor is likely to fail open, but failing shorted isn't unheard of. See also designs for wrist straps. I won't be trusting a single resistor to sit between me and a fire that could kill people. Trust me, if you use any plug in consumer grade electronics, you already are. Compact fluorescent bulbs are a particularly egregious example. By the way, for every 1M resistor type I am aware of, failing short circuit is essentially impossible. It could happen if the resistor is mounted with both ends in physical contact with a pcb trace, but that is a bad mechanical design that would compromise an optoisolator too. -Chuck Harris ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Trust me, if you use any plug in consumer grade electronics, you already are. Actually, we design plug-in consumer grade electronics here. No single point of failure is allowed to present line current to the user. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Let's not be obtuse on purpose, David. David VanHorn wrote: Trust me, if you use any plug in consumer grade electronics, you already are. Actually, we design plug-in consumer grade electronics here. No single point of failure is allowed to present line current to the user. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Let's not be obtuse on purpose, David. No amount of dancing is going to turn this into a design that is safe by any reasonable definition of the word. Safe in terms of it hasn't killed anyone yet is probably true. Safe in terms of you can trust this device not to cause a fire, no. To quote from the page: There are no safety worries about voltage, current or power, about frequency, shock or shorting. Worst-case current is only 60 µA so you can use thin digital wire to connect the plug to the microcontroller. One wire goes to Vss (signal ground) and the other to the microcontroller digital or analog input pin. If it doesn't work the first time, swap plug polarity. Or use capacitive coupling on both wires. Of course, the whole idea of this AC plug is unnerving at first but when you think about it, it makes sense. Better yet, just make one and test it for yourself. You should observe it tickles far less than a 9V battery (which I measured to be about 200 µA on a wet tongue). Does that last line actually suggest checking this contraption BY TOUCHING IT TO YOUR TONGUE??? No safety worries about voltage...or shorting ?? Resistors can and do fail shorted. They can also be damaged by line voltage transients and end up at some lower value. What version of safe applies here? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Do we think that failed shorted is rare? http://www.navsea.navy.mil/nswc/crane/sd18/Public%20Documents/Resistors/ResistorsFailure.pdf ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Yes, the paper even says so. The graph of failure rate is interesting. How useful is a graph that shows the failure rate of a general purpose film resistor as being from about 5E-10 to 8E-8 ? In any case, they are saying that 5% of a (to be pessimistic) 8E-8 phenomenon results in a short circuit... I think that qualifies as very rare. Put two resistors in series, and it becomes even more rare. -Chuck Harris David VanHorn wrote: Do we think that failed shorted is rare? http://www.navsea.navy.mil/nswc/crane/sd18/Public%20Documents/Resistors/ResistorsFailure.pdf ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
I'm sort of sorry I mentioned the PIC application note While I think it's time for this thread to die I'd like to make a couple of comments abot it tha have not been mentioned. 1/ ANY components connected directly to the mains supply should be desigined, rated and approved for this appliction. This includes the resistors. 2/ Placing heatshrink over the fusible resistors is not a good idea. It can upset the thermal properties and also is the heatshrink fire proof or just fire resistant? It would invalidate the creapage /clearance requirements (Mosture could possibly get underneath by capillary action) 3/ The original App note intended that ALL the line connected components (even via a resistor) should be in a permanantly closed or tool access only enclsoure, eithr double insulated or grounded. While I don't think Tom's interface is an immediate danger, I would not recommend it. It certainly would not pass EU LVD or North American UL / CSA regulations (I''ve designed equipment to meet to all three regulations at once). Note that a typical linline type Line driven laptop power supply can run quite a bit of AC leakage through the DC port due to EMC filter capacitors. On the 9V battery issue I've personally used a 9V battery driven datalogger in an opertaing theatre and they were happy with it's safety based on the 9V isolated operation (Yes it was connected to the patient). Robert G8RPI From: David VanHorn d.vanh...@elec-solutions.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Monday, 28 November 2011, 18:56 Subject: Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard Let's not be obtuse on purpose, David. No amount of dancing is going to turn this into a design that is safe by any reasonable definition of the word. Safe in terms of it hasn't killed anyone yet is probably true. Safe in terms of you can trust this device not to cause a fire, no. To quote from the page: There are no safety worries about voltage, current or power, about frequency, shock or shorting. Worst-case current is only 60 µA so you can use thin digital wire to connect the plug to the microcontroller. One wire goes to Vss (signal ground) and the other to the microcontroller digital or analog input pin. If it doesn't work the first time, swap plug polarity. Or use capacitive coupling on both wires. Of course, the whole idea of this AC plug is unnerving at first but when you think about it, it makes sense. Better yet, just make one and test it for yourself. You should observe it tickles far less than a 9V battery (which I measured to be about 200 µA on a wet tongue). Does that last line actually suggest checking this contraption BY TOUCHING IT TO YOUR TONGUE??? No safety worries about voltage...or shorting ?? Resistors can and do fail shorted. They can also be damaged by line voltage transients and end up at some lower value. What version of safe applies here? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
N.B. /tvb's adapter is NON-polarized. Jerry Don Latham wrote:Sorry, Brooke-I was not clear. I meant to not connect anything toneutral at all, but rather to depend on the ground connection alreadymade in the equipment for the low side of the signal, rather than a 1meg to neutral at the plug. Sorry.DonBrooke Clarkegt; Hi Don:gt;gt; Not a good idea. There are a number of fault conditions that can causegt; Neutral to be tens of volts above ground. Tom'sgt; circuit with a Meg in both the Hot and Neutral lines is much safer forgt; you equipment.gt;gt; Have Fun,gt;gt; Brooke Clarkegt; http://www.PRC68.comgt; http://www.End2PartyGovernment.com/gt;gt;gt; Don Latham wrote:gt;gt; well, grudgingly. only need the 1 meg to the hot side of the line, nogt;gt; connection to the neutral needed, with 1 meg in there, normal groundgt;gt; connections are going to supply the low side...It still lurks...gt;gt; Dongt;gt;gt;gt; Tom Van Baakgt;gt;gt;gt; Come on, folks. never hook anything directly to the power line. Thegt;gt;gt;gt; source is just too stiff. Use an opto. I used fiber optic isolationgt;gt;gt;gt; withgt;gt;gt;gt; my big DC power supply.gt;gt;gt;gt; Dongt;gt;gt; I used to agree, until actually tried it myself. Now this is howgt;gt;gt; I do my picPET 60 Hz data logging:gt;gt;gt;gt;gt;gt; Simple 60 Hz AC Mains Cycle Detectorgt;gt;gt; http://leapsecond.com/pages/ac-detect/gt;gt;gt;gt;gt;gt; /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
On Sat, 26 Nov 2011 12:08:41 -0800 Tom Van Baak t...@leapsecond.com wrote: Come on, folks. never hook anything directly to the power line. The source is just too stiff. Use an opto. I used fiber optic isolation with my big DC power supply. Don I used to agree, until actually tried it myself. Now this is how I do my picPET 60 Hz data logging: Simple 60 Hz AC Mains Cycle Detector http://leapsecond.com/pages/ac-detect/ Yes, there is nothing that speaks against connecting something directly to mains if you either ensure that the circuit is properly isolated or that the current is limited. But, i recomend to use two resistors in series to ensure that even if one fails, that the other prevents a possibly lethal hazard. Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
On Fri, Nov 25, 2011 at 1:21 PM, Robert Atkinson robert8...@yahoo.co.ukwrote: Hi, Microchip cerainly condone using input protection diodes of PIC devices as clamps. There are application notes for zero-crossing detection which connect the input to the 115V AC line via a resistor. Note that these are intentional protection diodes, not unavoidable parasitic junctions. Typical Absolute max clamp current (inc. 16F628) is +-20mA. Yes, absolute max - that below which the part doesn't let the magic smoke out... but note the comment below the absolute max ratings (I'm taking this from a PIC16F88 datasheet since I happen to be using this part): This is a stress rating only and functional operation of the device at those or any other conditions above those indicated in the operation listings of this specification is not implied. Exposure to maximum rating conditions for extended periods may affect device reliability. Note also the max voltage on any pin is something like Vdd+0.3V. One wonders how much conducting their diodes do with 0.3V across them. Personally, I don't let the protection diodes conduct in normal operation. Orin. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Come on, folks. never hook anything directly to the power line. The source is just too stiff. Use an opto. I used fiber optic isolation with my big DC power supply. Don Orin Eman On Fri, Nov 25, 2011 at 1:21 PM, Robert Atkinson robert8...@yahoo.co.ukwrote: Hi, Microchip cerainly condone using input protection diodes of PIC devices as clamps. There are application notes for zero-crossing detection which connect the input to the 115V AC line via a resistor. Note that these are intentional protection diodes, not unavoidable parasitic junctions. Typical Absolute max clamp current (inc. 16F628) is +-20mA. Yes, absolute max - that below which the part doesn't let the magic smoke out... but note the comment below the absolute max ratings (I'm taking this from a PIC16F88 datasheet since I happen to be using this part): This is a stress rating only and functional operation of the device at those or any other conditions above those indicated in the operation listings of this specification is not implied. Exposure to maximum rating conditions for extended periods may affect device reliability. Note also the max voltage on any pin is something like Vdd+0.3V. One wonders how much conducting their diodes do with 0.3V across them. Personally, I don't let the protection diodes conduct in normal operation. Orin. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon If you don't know what it is, don't poke it. Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
On Nov 26, 2011, at 10:36 AM, Don Latham wrote: Come on, folks. never hook anything directly to the power line. The source is just too stiff. Use an opto. I used fiber optic isolation with my big DC power supply. I don't disagree on isolation. I will say that Atmel's (and presumably Microchip's) app notes don't give much information on safe construction. Tom wrote a nice page showing a safer-than-average construction for sipping AC main voltage through high resistance: http://www.leapsecond.com/pages/ac-detect/ Kevin ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Clocking a PIC16F628A from a Rubidium Standard
How did such a trivial circuit function for a one-unit application trigger such a large philosophical discourse? I guess I'll put my one-cent's worth in too. If you were designing to make a mission-critical item, or millions of units, then every part and every penny would count, so the finesse requirement would be high, and the details critical. But this is not the case here. All you need is an NPN open collector - a simple Q circuit - or the output of an OC TTL or OD CMOS gate to eliminate the powered v. unpowered states issue. Let the gate or Q circuit be driven from the Rb source +5 V and 10 MHz signal, and let the collector/drain output be pulled up to the PIC supply. If there is concern that for some reason the gate open-device output may not work right when the gate is unpowered, then just build it and see, or just use a transistor circuit. Ed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Come on, folks. never hook anything directly to the power line. The source is just too stiff. Use an opto. I used fiber optic isolation with my big DC power supply. Don I used to agree, until actually tried it myself. Now this is how I do my picPET 60 Hz data logging: Simple 60 Hz AC Mains Cycle Detector http://leapsecond.com/pages/ac-detect/ /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
well, grudgingly. only need the 1 meg to the hot side of the line, no connection to the neutral needed, with 1 meg in there, normal ground connections are going to supply the low side...It still lurks... Don Tom Van Baak Come on, folks. never hook anything directly to the power line. The source is just too stiff. Use an opto. I used fiber optic isolation with my big DC power supply. Don I used to agree, until actually tried it myself. Now this is how I do my picPET 60 Hz data logging: Simple 60 Hz AC Mains Cycle Detector http://leapsecond.com/pages/ac-detect/ /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon If you don't know what it is, don't poke it. Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Hi Don: Not a good idea. There are a number of fault conditions that can cause Neutral to be tens of volts above ground. Tom's circuit with a Meg in both the Hot and Neutral lines is much safer for you equipment. Have Fun, Brooke Clarke http://www.PRC68.com http://www.End2PartyGovernment.com/ Don Latham wrote: well, grudgingly. only need the 1 meg to the hot side of the line, no connection to the neutral needed, with 1 meg in there, normal ground connections are going to supply the low side...It still lurks... Don Tom Van Baak Come on, folks. never hook anything directly to the power line. The source is just too stiff. Use an opto. I used fiber optic isolation with my big DC power supply. Don I used to agree, until actually tried it myself. Now this is how I do my picPET 60 Hz data logging: Simple 60 Hz AC Mains Cycle Detector http://leapsecond.com/pages/ac-detect/ /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
This area (SW Pennsylvania) we do not have galvanic ground distribution. So when a neutral is damaged all the load is forced back to the ground near the source. After some time the ground rod is completely corroded and does not provide a reliable earth sink. At this point there is no earth, and no network neutral. All 120 loads throw the balance out of whack and the local ground and neutral become a serious shock hazard. It's an interested condition where the safety circuity actually becomes live (because the network neutral is missing and the local ground is corrode) all grounded chassis become hot. It gets even more complicated depending how badly the ground rod is corroded, the original balance of the box (220 vs 120). I've seen 120 heat-lamp's back feed to 220 loads and act like slow blow fuses. I always use galvanic isolation on lines and neutrals. I've yet to find a solution to the live ground problem. Any ideas? Steve On Sat, Nov 26, 2011 at 4:50 PM, Brooke Clarke bro...@pacific.net wrote: Hi Don: Not a good idea. There are a number of fault conditions that can cause Neutral to be tens of volts above ground. Tom's circuit with a Meg in both the Hot and Neutral lines is much safer for you equipment. Have Fun, Brooke Clarke http://www.PRC68.com http://www.End2PartyGovernment.com/ Don Latham wrote: well, grudgingly. only need the 1 meg to the hot side of the line, no connection to the neutral needed, with 1 meg in there, normal ground connections are going to supply the low side...It still lurks... Don Tom Van Baak Come on, folks. never hook anything directly to the power line. The source is just too stiff. Use an opto. I used fiber optic isolation with my big DC power supply. Don I used to agree, until actually tried it myself. Now this is how I do my picPET 60 Hz data logging: Simple 60 Hz AC Mains Cycle Detector http://leapsecond.com/pages/ac-detect/ /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Sorry, Brooke-I was not clear. I meant to not connect anything to neutral at all, but rather to depend on the ground connection already made in the equipment for the low side of the signal, rather than a 1 meg to neutral at the plug. Sorry. Don Brooke Clarke Hi Don: Not a good idea. There are a number of fault conditions that can cause Neutral to be tens of volts above ground. Tom's circuit with a Meg in both the Hot and Neutral lines is much safer for you equipment. Have Fun, Brooke Clarke http://www.PRC68.com http://www.End2PartyGovernment.com/ Don Latham wrote: well, grudgingly. only need the 1 meg to the hot side of the line, no connection to the neutral needed, with 1 meg in there, normal ground connections are going to supply the low side...It still lurks... Don Tom Van Baak Come on, folks. never hook anything directly to the power line. The source is just too stiff. Use an opto. I used fiber optic isolation with my big DC power supply. Don I used to agree, until actually tried it myself. Now this is how I do my picPET 60 Hz data logging: Simple 60 Hz AC Mains Cycle Detector http://leapsecond.com/pages/ac-detect/ /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon If you don't know what it is, don't poke it. Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
On Thu, 24 Nov 2011 09:37:33 -0700 Robert Darlington rdarling...@gmail.com wrote: I've done this but don't remember the detail on the wiring. The data sheet made it clear though. One thing I did notice is that the oscillator seemed to power the chip! If I were doing it again I'd probably use some kind of powered buffer on the oscillator input so that when I power down the circuit it actually stops. This is why i mentioned the DC block capacitor. Even if you use a buffer, you would still power the PIC. The path in this case are the protection diodes on the input pin. By providing there an input voltage, you drive the upper diode which conducts the power to the VDD line which in turn powers the PIC. If you use a buffer, you get still the protection diodes and thus still the path to power the PIC (and the buffer). Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
On Thu, 24 Nov 2011 12:05:13 -0700 Kevin Rosenberg ke...@rosenberg.net wrote: Since frequency reference sine wave can exceed Vdd, you want to current limit the external clock. For example, an unterminated TBolt puts out 0-7V Pk-Pk. Atmel, in an app note where they hook up the pins of an AVR to 220V mains, states the over/under voltage protection diodes should not carry more than 1 milliamp of current. But, you should both read the datasheet for the output voltage of the Efratom and measure Pk-Pk voltage output at the point of your PIC. Using the protection diodes as part of the circuit is bad design practice. Use instead explicit shottky diodes (like BAT54S) for clamping. Better would be to use a resisitive divider (probably with a capacitive divider in parallel), a coupling capacitor to connect it to the clock input. You can limit the swing of the signal to less than 1V as the clock input doesnt require a big signal (when using a crystal, the signal can be as low as a few mV, depending on the chip) Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
On Nov 25, 2011, at 1:17 AM, Attila Kinali wrote: Using the protection diodes as part of the circuit is bad design practice. In general, I agree completely, Further, I think of operating outside of the datasheet may result in any manner of unspecified behavior. Basically, results while operating outside the datasheet specifications are unspecified. In this case, the use of the protection diode and the 1 ma limit comes directly from the manufacturer Atmel's App Note AVR182 [1]. That said, I'm cautious even when the manufacturer in an App Note says it's okay, but the use falls outside of the datasheet specifications. Thanks for the thoughts on an alternative circuit that doesn't rely on internal device knowledge that may, or may not, be okay. Kevin [1] http://www.atmel.com/dyn/resources/prod_documents/doc2508.pdf ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
On Fri, 25 Nov 2011 02:02:04 -0700 Kevin Rosenberg ke...@rosenberg.net wrote: In this case, the use of the protection diode and the 1 ma limit comes directly from the manufacturer Atmel's App Note AVR182 [1]. That said, I'm cautious even when the manufacturer in an App Note says it's okay, but the use falls outside of the datasheet specifications. Don't trust a datasheet blindly. Always apply common sense and a bit of caution. Especially when it comes to Atmel. In the past 2 years, i've discovered 3 silicon bugs in Atmel chips and two bugs in their documentation. Reporting the silicon bugs resulted in being completely ignored and the documentation bugs were answered with (literally) it's a silicon thing, completely disregarding the fact that following the documentation will cause hard to trace bugs in the software (that's how i discovered them in the first place). Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Attila, In the past 2 years, i've discovered 3 silicon bugs in Atmel chips and two bugs in their documentation. Reporting the silicon bugs resulted in being completely ignored and the documentation bugs were answered with (literally) it's a silicon thing, completely disregarding the fact that following the documentation will cause hard to trace bugs in the software (that's how i discovered them in the first place). Can you please contact me offline at df...@ulrich-bangert.de for a discussion on this topic? I use lots of ATTINY85, ATMEGA32 and ATMEGA2560 and have also discovered some issues with ATMEL processors (specially with the 32). Want to learn more about what you found. Best regards Ulrich -Ursprungliche Nachricht- Von: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] Im Auftrag von Attila Kinali Gesendet: Freitag, 25. November 2011 13:14 An: Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard On Fri, 25 Nov 2011 02:02:04 -0700 Kevin Rosenberg ke...@rosenberg.net wrote: In this case, the use of the protection diode and the 1 ma limit comes directly from the manufacturer Atmel's App Note AVR182 [1]. That said, I'm cautious even when the manufacturer in an App Note says it's okay, but the use falls outside of the datasheet specifications. Don't trust a datasheet blindly. Always apply common sense and a bit of caution. Especially when it comes to Atmel. In the past 2 years, i've discovered 3 silicon bugs in Atmel chips and two bugs in their documentation. Reporting the silicon bugs resulted in being completely ignored and the documentation bugs were answered with (literally) it's a silicon thing, completely disregarding the fact that following the documentation will cause hard to trace bugs in the software (that's how i discovered them in the first place). Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
On Fri, Nov 25, 2011 at 12:17 AM, Attila Kinali att...@kinali.ch wrote: On Thu, 24 Nov 2011 12:05:13 -0700 Kevin Rosenberg ke...@rosenberg.net wrote: Since frequency reference sine wave can exceed Vdd, you want to current limit the external clock. For example, an unterminated TBolt puts out 0-7V Pk-Pk. Atmel, in an app note where they hook up the pins of an AVR to 220V mains, states the over/under voltage protection diodes should not carry more than 1 milliamp of current. But, you should both read the datasheet for the output voltage of the Efratom and measure Pk-Pk voltage output at the point of your PIC. Using the protection diodes as part of the circuit is bad design practice. Use instead explicit shottky diodes (like BAT54S) for clamping. I agree entirely. I had an AtoD converter that if I let the protection diodes conduct at all, would be several counts out. In this case, even a schottky diode wasn't enough! I ended up clamping to slightly less than Vdd using a schottky diode and a TL431 to provide about Vdd-0.2V. Orin. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Hi, Microchip cerainly condone using input protection diodes of PIC devices as clamps. There are application notes for zero-crossing detection which connect the input to the 115V AC line via a resistor. Note that these are intentional protection diodes, not unavoidable parasitic junctions. Typical Absolute max clamp current (inc. 16F628) is +-20mA. As a side note, when using these diodes for ESD protection, Microchip recommend using 0.01uF supply decoupling capacitors close to the chip rather than 0.1uF. This reduces the peak current. Trace inductance limits the effect of more distant capacitive loading. Robert G8RPI. From: Attila Kinali att...@kinali.ch To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, 25 November 2011, 8:17 Subject: Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard On Thu, 24 Nov 2011 12:05:13 -0700 Kevin Rosenberg ke...@rosenberg.net wrote: Since frequency reference sine wave can exceed Vdd, you want to current limit the external clock. For example, an unterminated TBolt puts out 0-7V Pk-Pk. Atmel, in an app note where they hook up the pins of an AVR to 220V mains, states the over/under voltage protection diodes should not carry more than 1 milliamp of current. But, you should both read the datasheet for the output voltage of the Efratom and measure Pk-Pk voltage output at the point of your PIC. Using the protection diodes as part of the circuit is bad design practice. Use instead explicit shottky diodes (like BAT54S) for clamping. Better would be to use a resisitive divider (probably with a capacitive divider in parallel), a coupling capacitor to connect it to the clock input. You can limit the swing of the signal to less than 1V as the clock input doesnt require a big signal (when using a crystal, the signal can be as low as a few mV, depending on the chip) Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
As far as the atmel (avr): Almost all my projects use AVR microcontrollers, Due to the RD nature of my work I've /always/ pushed the envelope. I use data sheets as a guideline and nothing else. Years ago I poked around publically at the avr forum about the idea of exploiting undocumented instructions. People in general were not interested in anything out documentation parlance. *Burn in * is second nature to me. Both profiling and application. As far as powering down a MCU while keeping a clock running, The easiest solutions i've found are to use a field effect, i prefer jfet but signal fets would work just as well. This way you don't need to be concerned about back feeding power from IO or in this case the clock/oscillator input. Steve On Fri, Nov 25, 2011 at 4:21 PM, Robert Atkinson robert8...@yahoo.co.ukwrote: Hi, Microchip cerainly condone using input protection diodes of PIC devices as clamps. There are application notes for zero-crossing detection which connect the input to the 115V AC line via a resistor. Note that these are intentional protection diodes, not unavoidable parasitic junctions. Typical Absolute max clamp current (inc. 16F628) is +-20mA. As a side note, when using these diodes for ESD protection, Microchip recommend using 0.01uF supply decoupling capacitors close to the chip rather than 0.1uF. This reduces the peak current. Trace inductance limits the effect of more distant capacitive loading. Robert G8RPI. From: Attila Kinali att...@kinali.ch To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, 25 November 2011, 8:17 Subject: Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard On Thu, 24 Nov 2011 12:05:13 -0700 Kevin Rosenberg ke...@rosenberg.net wrote: Since frequency reference sine wave can exceed Vdd, you want to current limit the external clock. For example, an unterminated TBolt puts out 0-7V Pk-Pk. Atmel, in an app note where they hook up the pins of an AVR to 220V mains, states the over/under voltage protection diodes should not carry more than 1 milliamp of current. But, you should both read the datasheet for the output voltage of the Efratom and measure Pk-Pk voltage output at the point of your PIC. Using the protection diodes as part of the circuit is bad design practice. Use instead explicit shottky diodes (like BAT54S) for clamping. Better would be to use a resisitive divider (probably with a capacitive divider in parallel), a coupling capacitor to connect it to the clock input. You can limit the swing of the signal to less than 1V as the clock input doesnt require a big signal (when using a crystal, the signal can be as low as a few mV, depending on the chip) Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Greetings all, I have an Efratom 101 frequency standard with a 10 MHz TTL otput. I want to use this to clock a PIC 16F628A so I can make a frequency counter with a resolution of 1 Hz. I am going to use the design by EI9GQ here http://homepage.eircom.net/~ei9gq/counter.html . What I need to know is how i should go about electronically interfacing the TTL output from the rubidium standard so that it can clock the PIC. Has anyone on the list actually done this successfully? Thanks in advance, Steve G0XAR -- It is vain to do with more that which can be done with less.William of Occam Christmas has become a marketing gimmickany relationship between it and the celebration of charity, good will, peace to all mankind and the birth of Jesus are entirely co-incidental and I find this incredibly sad! ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
On Thu, 24 Nov 2011 14:41:24 + Stephen Farthing squir...@gmail.com wrote: I have an Efratom 101 frequency standard with a 10 MHz TTL otput. I want to use this to clock a PIC 16F628A so I can make a frequency counter with a resolution of 1 Hz. I am going to use the design by EI9GQ here http://homepage.eircom.net/~ei9gq/counter.html . What I need to know is how i should go about electronically interfacing the TTL output from the rubidium standard so that it can clock the PIC. Has anyone on the list actually done this successfully? Have a look at the PIC 16F628 data sheet, it will tell you the requirements for the clock input and there should be circuit for external clock signal listed. If it's not in the datasheet, it should be in an appnote. Usually, chips accept sinusoidal and rectangular inputs up to 0V-VDD swing. If i'm reading the schematic correctly and the PIC runs with 5V, then you should be able to just feed the Efratom output directly to the PIC. Maybe, a ceramic 100n capacitor in this line should be used to do a DC isolation (1u cermaic should do as well). Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
I've done this but don't remember the detail on the wiring. The data sheet made it clear though. One thing I did notice is that the oscillator seemed to power the chip! If I were doing it again I'd probably use some kind of powered buffer on the oscillator input so that when I power down the circuit it actually stops. -Bob On Thu, Nov 24, 2011 at 7:50 AM, Attila Kinali att...@kinali.ch wrote: On Thu, 24 Nov 2011 14:41:24 + Stephen Farthing squir...@gmail.com wrote: I have an Efratom 101 frequency standard with a 10 MHz TTL otput. I want to use this to clock a PIC 16F628A so I can make a frequency counter with a resolution of 1 Hz. I am going to use the design by EI9GQ here http://homepage.eircom.net/~ei9gq/counter.html . What I need to know is how i should go about electronically interfacing the TTL output from the rubidium standard so that it can clock the PIC. Has anyone on the list actually done this successfully? Have a look at the PIC 16F628 data sheet, it will tell you the requirements for the clock input and there should be circuit for external clock signal listed. If it's not in the datasheet, it should be in an appnote. Usually, chips accept sinusoidal and rectangular inputs up to 0V-VDD swing. If i'm reading the schematic correctly and the PIC runs with 5V, then you should be able to just feed the Efratom output directly to the PIC. Maybe, a ceramic 100n capacitor in this line should be used to do a DC isolation (1u cermaic should do as well). Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
On Nov 24, 2011, at 7:50 AM, Attila Kinali wrote: Have a look at the PIC 16F628 data sheet, it will tell you the requirements for the clock input and there should be circuit for external clock signal listed. If it's not in the datasheet, it should be in an appnote. Usually, chips accept sinusoidal and rectangular inputs up to 0V-VDD swing. If i'm reading the schematic correctly and the PIC runs with 5V, then you should be able to just feed the Efratom output directly to the PIC. Maybe, a ceramic 100n capacitor in this line should be used to do a DC isolation (1u cermaic should do as well). Tom's picPET page http://www.leapsecond.com/pic/picpet.htm describes using a TBolt sine directly as a clock source. I'm going something similar with AVRs for an external clock. Since frequency reference sine wave can exceed Vdd, you want to current limit the external clock. For example, an unterminated TBolt puts out 0-7V Pk-Pk. Atmel, in an app note where they hook up the pins of an AVR to 220V mains, states the over/under voltage protection diodes should not carry more than 1 milliamp of current. But, you should both read the datasheet for the output voltage of the Efratom and measure Pk-Pk voltage output at the point of your PIC. To limit to 1 ma for an AVR with a TBolt, you'd want to use a 2K series resistor to drop that extra 2V (7V Pk vs. 5V Vdd) to a milliamp of current. Kevin ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
One thing I did notice is that the oscillator seemed to power the chip! If I were doing it again I'd probably use some kind of powered buffer on the oscillator input so that when I power down the circuit it actually stops. That's a reasonably common problem. Occasionally it's a feature. Most digital inputs have protection diodes from the input pin to VCC and GND. They come for free in most semiconductor technologies. They damp out glitches/reflections. If VCC is open and the circuit isn't drawing a lot of power, you can get enough power from an input signal through the diode to power the whole circuit. It can be nasty to debug if you have something like VCC open to a single chip. The outputs of that chip will be a diode drop lower than the rest of the circuit. I thought about setting up a PIC to make 32 KHz from 10 MHz using power from the 10 MHz input signal but never got around to actually building it. -- It's tricky to safely connect to external signals that may be active when the local power is off. I'm not sure a powered buffer will solve the problem, at least without some more info about what type of buffer you plan to use. In the simple case, you can just insert a big-enough resistor. It needs to be big enough to limit the input current yet small enough not to distort the input signal too much. There are some families of chips made without the protection diodes. The usual application is letting chips running on 3.3V listen to signals from chips running on 5V. (I don't have part numbers handy.) -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Clocking a PIC16F628A from a Rubidium Standard
I have an Efratom 101 frequency standard with a 10 MHz TTL otput. I want to use this to clock a PIC 16F628A so I can make a frequency counter with a resolution of 1 Hz. I am going to use the design by EI9GQ here http:// homepage.eircom.net/~ei9gq/counter.html . What I need to know is how i should go about electronically interfacing the TTL output from the rubidium standard so that it can clock the PIC. Has anyone on the list actually done this successfully? It will probably just work, but you need to read both data sheets to check the details. TTL isn't well defined. It may mean that it's a digital signal rather than a sine wave. It may mean that it's TTL volltage levels rather than CMOS. One common output setup is a strong CMOS driver (typically several sections of a chip in parallel) running on 5V with a series 50 ohm resistor. If the receiving end is terminated with a 50 ohm resistor you will see a 2.5V signal. Without the terminator you will see 5V and overshoot/reflections if the cable is long relative to the rise time. 2.5V is close to the old TTL signal levels. The PIC clock circuitry can run in several modes. (This from memory and I may be forgetting something or confusing it with other chips.) The data sheet or an app note should have the details. One mode is for crystals. It takes 2 pins. Internally, there is an amplifier. There may be a separate mode for slow (low power) crystals such as 32 KHz. There is another mode for an external signal on the clock-in pin. It's intended for things like this. If I was doing something like this, I'd probably start with a 50 ohm input terminator and a 10K resistor over to the clock input pin. Then I'd go check both data sheets to verify that it would work correctly. Do you have a scope? -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Clocking a PIC16F628A from a Rubidium Standard
Stephen, As well as limiting the input voltage swing into the PIC with a ~2k2 resistor, add an additional 4k7 or 10k resistor (AOT) across the PIC's Vcc rail to ground. This swamps the rectified DC produced by the input drive signal when the PIC DC supply is removed. I've used /tvb's PIC divider in a few projects and experienced the same it's still working phenomenon. Took a while before twigging the input protection diodes were responsible for these unintended consequences. Kit VK2LL On Nov 24, 2011, at 7:50 AM, Attila Kinali wrote: Have a look at the PIC 16F628 data sheet, snip Since frequency reference sine wave can exceed Vdd, you want to current limit the external clock snip To limit to 1 ma for an AVR with a TBolt, you'd want to use a 2K series resistor to drop that extra 2V (7V Pk vs. 5V Vdd) to a milliamp of current. Kevin ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
