I tried my new circuit with the optocouplers using 270k for R5 & R6 and 1k
for R3 & R4.
It works within the limits of +0v and about -22v. It is interesting that
the other circuit did not work for low + bias. It must be the slower
positive edge as someone mentioned. I will use about +30 and -30v, whatever
the rectified transformer gives.
This is my preliminary software. It only counts up at present from 0 to 9
fast (10Hz) slowing down to 1Hz then repeating. The delay between the
steering pulses depends on the speed so at 1 Hz you can actually see every
pin lit. I thought it a waste to not see them. I have not fully tried this
software, only a Dekatron test version, so if there are errors please
forgive me. There is a BCD version that also works. I may add a "Spinner"
between 0 to 9 counts in place of the 2 second delay, 1 second forwards and
1 second backwards.
// main loop
while (1) // loop endlessly
{
for(j=1;j<=10;j++) // sets the delays
{
for(i=0;i<=9;i++) // the BCD digit displayed (Nixies, etc)
{
// generate clock and BCD
output_high(pin_C4); // high for 10 uS
delay_us(10);
output_low (pin_C4); // end pulse
portC = i; // output BCD
// Dekatron clocking
output_high(pin_A5); // steering ring 1
delay_ms(j*50);
output_high(pin_A4); // steering ring 2
delay_ms(j*50);
output_low (pin_A5);
delay_ms(j*50);
output_low (pin_A4);
// period of sequence
delay_ms(j*100); // set period
} //end for i loop
delay_ms(2000); // wait 2 seconds after each 0 to 9 count
} //end for j loop
} //end of endless while loop
} // end of main function
On Wed, Feb 17, 2021 at 4:00 PM Jon <[email protected]> wrote:
> No hard figures - it's dependent on a bunch of factors; principally
> manufacturing quality, how you use the tube, operating temperature and gas
> fill. If you keep the operating current within spec and preferably at the
> lower end, avoid the tube getting heated from its surroundings and above
> all else keep the glow moving around all of the electrodes, they will last
> a seriously long time. The electrical properties will change gradually -
> the maintaining voltage rises and the latitude around the voltages required
> for reliable stepping decreases. So you were absolutely right to point out
> the importance of taking note of these elements of the spec when designing
> - you can get away with a lot on a NIB tube, but progressively less with
> age. Of course if the application requires clear glass to see the lovely
> glow, then the tube may reach end of its useful life in that application as
> sputtering gradually obscures the view, and that may happen well before it
> ceases to step reliably.
>
> I'm not surprised by gregebert's description of his A101 - his application
> sounds like a great recipe for a long dekatron life. The slow speed ones
> are tough as anything and they love to work! Just for context, I believe
> that the large majority of dekatrons working in the stores of the WITCH
> today are from the original complement of tubes the machine was built with
> at the start of the 1950s. Can't formally prove it of course, but the date
> codes are consistent with that. Also, as we've noted before on other
> Russian glow tubes, the guaranteed life spans on the datasheets are
> ridiculously conservative if the tubes are treated well. The A101 datasheet
> gives a 1000 hour life - his A101 has done 70x that! I have a similar
> experience with my IN9 clock - the prototype unit is still going strong on
> its original tubes after 120K hours - datasheet life is 1K hours.
>
> Note that we're talking here about use-related life limitation - the death
> in storage of the high-speed dekatrons is a whole different topic.
>
> Jon.
>
> On Tuesday, February 16, 2021 at 8:49:07 PM UTC Dekatron42 wrote:
>
>> No, unfortunately not, no hard figures - maybe Jon has. I've only read in
>> some books about dekatron construction (neon tube construction in general
>> where dekatrons are shown as special variations) that they have similar
>> lifespans compared to small neon lamps but that the complex design
>> complicates the failure modes/rate and also that keeping currents/voltages
>> within the values specified in the datasheet will guarantee that they work
>> as long as possible.
>>
>> It depends on when you say a dekatron fails, it can get a silvery finish
>> on the glass so you almost can't see the glow but it still works and it can
>> fail a lot earlier than that due to internal flash-overs due to sputtering
>> onto the ceramic material which means a current can flow in this sputtered
>> material as the distance is shorter there compared to other paths (I have a
>> few dekatrons with that failure and of course a few with a silvery look).
>>
>> I have to count my dekatrons one day to see if I have enough to build a
>> second Harwell WITCH..... ;) :)
>>
>> /Martin
>>
>> On Tuesday, 16 February 2021 at 17:16:07 UTC+1 gregebert wrote:
>>
>>> *Martin* - Do you know how long dekatrons last ? I have an A-101
>>> running as a spinner in one of my clocks, and it's been going 60RPM 24/7
>>> for almost 8 years with no signs of degradation. I use 30k dropping
>>> resistors at the cathodes, and the current is right at the spec value of
>>> 450uA, so that gives about 15V for "steering", and the driving waveform is
>>> 3-phase with overlap. I
>>>
>>> On Tuesday, February 16, 2021 at 4:15:05 AM UTC-8 Dekatron42 wrote:
>>>
>>>> There is one more dimension to think about when running a dekatron and
>>>> that is that over time it will degrade due to sputtering affecting the
>>>> electrodes and to maintain a correct counting when it ages you should keep
>>>> the voltages as described in the datasheet, especially the guide and bias
>>>> voltages as those are needed when the dekatron nears its end of life - it
>>>> is the same effect that is in play if you want to raise a dekatron from the
>>>> dead if it has been heavily used or just stored for a very long time
>>>> without use, raise the bias/pulse voltages and sometimes the anode voltage
>>>> to surpass the effects of the sputtering - effectively increasing the
>>>> current flow between the anode and the guides/cathodes.
>>>>
>>>> So even if dekatrons work at other voltages you will see the effects of
>>>> lower/incorrect voltages when they near their end of life, this has been
>>>> described in older litterature where the internals of dekatrons has been
>>>> disected in detail - you might just need some 10V below the glowing cathode
>>>> to move the glow on a new dekatron but as it ages it will stop working at
>>>> that voltage.
>>>>
>>>> /Martin
>>>>
>>>> On Tuesday, 16 February 2021 at 00:53:36 UTC+1 [email protected] wrote:
>>>>
>>>>> Those values were left over from the 5v circuit. I was more concerned
>>>>> with the level shifting from the PIC at 0 to +5v.
>>>>> Peter
>>>>>
>>>>> On Mon, Feb 15, 2021 at 6:48 PM Jon <[email protected]> wrote:
>>>>>
>>>>>> I'd had a similar thought about increasing the bias resistors - it's
>>>>>> not necessary to run so much current (5mA) through that part of the
>>>>>> circuit.
>>>>>>
>>>>>> OK, so your proposed conditions are that the dekatron will see are
>>>>>> 400V anode to main cathodes; guides swinging from +25V to -25V with
>>>>>> respect
>>>>>> to main cathodes. Tube current will be about 345uA.
>>>>>> I've replicated these on my dekatron tester using a nice NIB GS10C/S
>>>>>> as the test subject and can confirm that they do work - the tube stepped
>>>>>> fine up at speeds up to over 4kpps once I'd woken it up a bit.
>>>>>>
>>>>>> Caveats:
>>>>>> 1) I only tried one tube.
>>>>>> 2) My circuit is rather different to yours so although the static
>>>>>> voltages are the same, the pulse shapes are almost certainly different.
>>>>>> And
>>>>>> we didn't even talk yet about pulse durations, so I've no idea what your
>>>>>> PIC is spitting out. But as long as you're not trying to cut things too
>>>>>> fine, there's lots of latitude to find patterns that work. Keep things
>>>>>> north of 100us per phase and you'll be fine unless you've got a really
>>>>>> reluctant tube.
>>>>>> 3) I was running at slightly lower current (300uA) so you've probably
>>>>>> got a bit more margin for speed than I had. Recommended operating
>>>>>> conditions are 325uA +/- 20%, so we're both inside that range. But a
>>>>>> little
>>>>>> more rather than less current is useful when pushing higher speeds. I'm
>>>>>> guessing though that you're looking for a much slower stepping speed for
>>>>>> this application though.
>>>>>>
>>>>>> If you've not already done so, I'd definitely second Martin's
>>>>>> recommendation to take a look at Michael Moorrees' dekatron work (he
>>>>>> looks
>>>>>> in here from time to time too). He used a couple of elegant design tricks
>>>>>> which simplify the interfacing of dekatrons to modern electronics /
>>>>>> microcontrollers - I've followed his approach in pretty much all the
>>>>>> stuff
>>>>>> I've built and it works a treat. Not to say that other approaches aren't
>>>>>> equally useful too of course.
>>>>>>
>>>>>> Jon.
>>>>>>
>>>>>> On Monday, February 15, 2021 at 9:39:13 AM UTC Dekatron42 wrote:
>>>>>>
>>>>>>> I'd raise the resistance to at least some 100k for the two bias
>>>>>>> resistors R5 & R6 in your diagram above.
>>>>>>>
>>>>>>> I'd also use the correct bias voltage and just use an MPSA42 with
>>>>>>> its emitter to common ground for the driver to simplify the circuit as
>>>>>>> Ronald Dekker and Michael Moorrees with their dekatron circuits.
>>>>>>>
>>>>>>> Different dekatrons need different bias and pulse voltages on the
>>>>>>> guide electrodes to count properly so accomodating for those
>>>>>>> requiremenst
>>>>>>> will remove a lot of problems and keep down the fault finding time.
>>>>>>>
>>>>>>> /Martin
>>>>>>> On Monday, 15 February 2021 at 03:05:12 UTC+1 [email protected]
>>>>>>> wrote:
>>>>>>>
>>>>>>>> You are absolutely right. 5v was not high enough despite Ronald's
>>>>>>>> and my confirmation that it would work.
>>>>>>>> I am changing to +25v and -25v and will have an optocoupler with
>>>>>>>> the diode driven from the 5v PIC and the transistor at the bottom of
>>>>>>>> the
>>>>>>>> resistor between the two power supplies. It keeps it simple. I have to
>>>>>>>> order the optocoupler because none of my old ones have higher than 30 v
>>>>>>>> rating.
>>>>>>>> I will have to think about the extra two power supplies. Maybe I
>>>>>>>> can't avoid them. It will be a few days until I get the parts.
>>>>>>>> Peter
>>>>>>>> [image: Dekatron Circuit.jpg]
>>>>>>>>
>>>>>>>> On Sun, Feb 14, 2021 at 3:18 PM Jon <[email protected]> wrote:
>>>>>>>>
>>>>>>>>> Interesting approach - not seen it rigged up quite like that. Let
>>>>>>>>> us know how it goes!
>>>>>>>>>
>>>>>>>>> My immediate question is whether there's a big enough potential
>>>>>>>>> difference between an inactive guide and a main cathode to get a
>>>>>>>>> reliable
>>>>>>>>> transfer forward from a deactivating G2 to the 'next' main cathode
>>>>>>>>> rather
>>>>>>>>> than back to the adjacent recently used G1 - 5V is much lower than the
>>>>>>>>> datasheet guide bias. Might be OK at slow stepping speeds with long
>>>>>>>>> guide
>>>>>>>>> pulses. Also the leading edge of your guide pulses is going to be
>>>>>>>>> fairly
>>>>>>>>> slow as Q1/2 come out of saturation and the guides are passively
>>>>>>>>> pulled
>>>>>>>>> down to the 'active' voltage. Most guide drive circuits use a NPN
>>>>>>>>> pull-down
>>>>>>>>> to the active state which creates a sharp leading edge and then a
>>>>>>>>> slower
>>>>>>>>> return to the inactive state.
>>>>>>>>>
>>>>>>>>> Jon.
>>>>>>>>>
>>>>>>>>> On Sunday, February 14, 2021 at 7:06:28 PM UTC [email protected]
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>> Having finished the Amperex 8453 display I started on my
>>>>>>>>>> Dekatron. Thanks to all for the suggestions.
>>>>>>>>>> I read up on Ronald Dekker's clock project
>>>>>>>>>> https://www.dos4ever.com/decatron/decatronweb.html
>>>>>>>>>> and decided against a direct drive from a 74141 because, even if
>>>>>>>>>> it was practical, it would not look as good as using all the pins.
>>>>>>>>>> It would
>>>>>>>>>> look like the 8453 I just finished except without the number mask.
>>>>>>>>>> A few quick experiments showed that a -24v power supply was
>>>>>>>>>> needed for the easiest implementation.. This is my design. I will
>>>>>>>>>> let you
>>>>>>>>>> know if it works.
>>>>>>>>>>
>>>>>>>>>> A PIC drives the circuit: it starts with Q3 off to force a start
>>>>>>>>>> at 1. A high on R3 or R4 is the same as the switches in Ron's test
>>>>>>>>>> circuit
>>>>>>>>>> placing -24v on the guides. As my PIC sends the BCD for the other
>>>>>>>>>> displays
>>>>>>>>>> and clocks the E1T it will generate the sequence to advance or
>>>>>>>>>> retard this
>>>>>>>>>> Dekatron..
>>>>>>>>>> [image: Dekatron Circuit.jpg]
>>>>>>>>>>
>>>>>>>>> --
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>>>>>>>>> .
>>>>>>>>>
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>>>>>>
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