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.
