If you take 7.3k resistors rather than 3.65k resistors, the tubes will only be 6dB less bright which is not significant. If that increases tube life, I would say, that is the better choice as you pointed out already.
For blanking, I think Adam means to send a hex number (0x0A) to the 74141 (D=1; C=0; B=1; A=0). According to the datasheet, this would lead to a correct blanking of the tubes. For my clock I am designing a module as I am not really a fan to use these types of old TTL logic. It's a 24 pin module that fits into a DIP24 IC socket. It basically mimics the 74141 but has high voltage output mosfets (240V) and the 4 inputs can be latched, so you don't need extra latches as required by the standard 74141. It also offers a blanking input, either by writing 0x0a or using a dedicated pin (which is convenient for PWM dimming). It can be interfaced with MCU or arduino. Michel On Mar 19, 6:21 am, Imbanon <[email protected]> wrote: > Hey Cobra! Thanks you for your explanation. I see what you did there, > and you are quite correct. But the thing is that I did not calculate > anything using power. You are completely right with the brightness, > but I do not want the same brightness as with direct drived nixies. I > lean towards tube life, and I think that the only way to achieve this > is by getting the correct current, and that would be around 2mA. > > I will make a schematic and share it, hopefully tomorrow, if I find > some time. > > My first design was 1x6, but I wasn't happy with the brightness. It > also required some higher current peaks, which can't be good for the > tubes. 2x3 mux design gives better brightness, but uses one more pin. > > And can someone please explain how does one blank a 74141? Adam, what > do you mean by setting the input to A? Setting a logic 1 to the A > input pin by the datasheet? That only sets the output to "1". My > design so far didn't use blanking with the 74141's. I just turned all > anodes off for 200us, and I never had any ghosting problems or > anything like that. > > Cheers > > On Mar 17, 6:35 am, Cobra007 <[email protected]> wrote: > > > > > > > > > Hi Imbanon, > > > I followed your calculations for quite a bit and was also wondering > > why your measurements are so much different than your calculations. My > > calculation suggest that you need a 7.3k resistor for each tube. This > > means if you have 2 tubes with a common anode connected to 1 resistor, > > and switch both tubes on at the same time (which you say you do), then > > you need to half the resistor. In that case, 3.65k. > > > Now, I was also puzzled why my resistor calculation results in half of > > your resistor calculation. The answer is in fact quite simple, and I > > will try to explain to you. > > > First of all, we need to agree that the tube power needs to be the > > same in both direct drive as well as multiplexed mode to guarantee > > equal tube brightness. Therefore Pdc = Prms > > > Pdc = Udc * Idc > > and also > > Prms = Urms * Irms > > > Do you notice the problem already? > > > Pdc = 145V * 2mA = 0.29W > > > Prms = 145*sqrt(T1/T) * Irms > > > So, Irms should be 0.29 / Urms = 0.29 / (145*sqrt(T1/T)) = 3.9mA > > > Your calculation was based on the fact that Irms had to be 2mA, but > > this is not correct because it needs to be 3.9mA. > > The peak current through the resistor is then 3.9mA / sqrt(T1/T) = > > 7.5mA per tube (15mA if 2 tubes are switched on at the same time). > > This is exactly what you get if you take the average currents. You > > want 12mA average current (6 tubes * 2mA). which is 12mA / (26.7 / > > 33.3) = 15mA. > > > Unknowingly, to calculate Prms you were multiplying Irms * Udc, not > > Irms * Urms. > > > Does this make sense? > > > I do agree with the rest of the guys that 6 resistors (7.3k) would be > > better that 3 resistors (3.65k), it will split the current more evenly > > through the 2 tubes. > > > Michel > > > On Mar 17, 6:18 am, Imbanon <[email protected]> wrote: > > > > First of all, thank you all for your support. Feels great to have some > > > people with knowledge behind my back. > > > So many replies since I had time to check the group last time that I > > > don't know where to start :) > > > > I do not have a schematic for my design, as it is my own design that I > > > pretty much pull out of my head as I go. That often shown like a bad > > > idea, making me to change a lot of things afterwards. Just like today, > > > I had to rewire the whole 'spider web'. And that was the second time I > > > had to do it! > > > And I have to clear out that I have a common anode resistor for 2 > > > tubes, making a total of 3 anode resistors for all 6 tubes. That means > > > that the current has to be double (resistance cut by half). I hope > > > that it now explains the rounded 8mA (7.74 to be more precise) on the > > > anode resistor. It cuts to two nixies, giving appox 3.87mA peak > > > current to each tube. So then 3.87*sqrt(0.267)=2mA RMS > > > Anyhow, I do believe that I have to use the RMS values when working > > > with multiplexed designs, rather than average. Just like someone > > > already explained why, because of the power dissipation. I really hope > > > it is that way :) > > > > Well that's all for now. I hope that my setup with anode resistors is > > > finally done. If not - I still have another week to use all the fancy > > > expensive oscilloscopes! So if anyone doesn't agree with this, please > > > say the word :) > > > > Cheers > > > > On Mar 16, 9:13 am, Dekatron42 <[email protected]> wrote: > > > > > Many manufacturers write that you will have to contact them for the > > > > special curves you need when you are going to multiplex their Nixies > > > > since they do not usually print that information in the databooks. > > > > > These sheets show you that the Nixie will have an increased turn-on > > > > voltage corresponding to the increased current when run in switched > > > > mode. This is the same as when a neon voltage stabilizer tube is used, > > > > the voltage increases somewhat when the current increases, you can > > > > check the OB2 voltage regulator tube for instance. > > > > > The curves for most Nixies when used in multiplexed mode are not > > > > linear so if you can't find those curves you'll have to make the > > > > measurements yourself and take into account the spread between > > > > different Nixies to draw the curve. Some of these special curves have > > > > a voltage span of approximately 10-30V for a certain current through > > > > the Nixie, so there is an upper and a lower limit for the turn-on > > > > voltage corresponding to the current used. > > > > > This book:http://www.oldtimeradio.de/BU7908.php"Electronica 171 - > > > > Elektronische Anzeigebauelemente" by Winfired Müller contains a few of > > > > these curves for the ZM-series of Nixies. > > > > > /Martin > > > > > On 16 mar, 00:55, Cobra007 <[email protected]> wrote: > > > > > > Yes, I think I mentioned "slightly" increase rather than a mayor > > > > > increase. > > > > > > I have measure this on another nixie tube and came to the following > > > > > voltages: > > > > > 0.5mA : 120V > > > > > 1.0mA : 125V > > > > > 1.5mA: 130V > > > > > 2.0mA: 133V > > > > > 3.0mA: 140V > > > > > 4.5mA: 150V > > > > > > His tube current will increase from 2mA to about 7.5mA, so according > > > > > to the above measurements, the increase in tube voltage will be > > > > > playing a role. > > > > > > Michel > > > > > > On Mar 16, 10:06 am, Charles MacDonald <[email protected]> wrote: > > > > > > > On 12-03-15 05:46 AM, Cobra007 wrote: > > > > > > > > So it looks like your resistor is correct. The only thing is that > > > > > > > the > > > > > > > voltage across the tube will slightly increase due to the higher > > > > > > > current, so it's not 100% correct but pretty much. > > > > > > > Since we are talking a Neon device, the voltage across the tube > > > > > > will try > > > > > > to stay the same, with the current adjusting if needed. That is why > > > > > > Neon bulbs were used as Voltage reference devices in days of Old. > > > > > > > -- > > > > > > Charles MacDonald Stittsville Ontario > > > > > > [email protected] Just Beyond the > > > > > > Fringehttp://users.trytel.com/~cmacd/tubes.html > > > > > > No Microsoft Products were used in sending this e-mail. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
