You beat me to writing a similar reply to the original post, but I wanted to expand on your use of the lines-powered transformer. One way to completely avoid dealing with the direct AC line at all (although not high voltages, of course) is to use back-to-back low voltage transformers. An off-the-shelf 12-volt AC "wall wart" can then be plugged into a jack on your project that connects to the secondary of a 12.6V filament transformer. If you ever decide to sell one of these, this is a *huge* benefit, because it completely short-circuits (so to speak) the entire UL/CSA approval process. This also gives you the option of adjusting the final output voltage, by simply using another voltage wall wart (9 or 15 VAC, for example). Note that the inexpensive wall warts *always* run high in voltage at less than their rated load.
One thing to consider would be the addition of a filter capacitor to this circuit. As others have said, the glow of the IN-9 tends to detach from the bottom if it sees too much of a transient, and this includes the power supply. Conversely, other people seem to have had good luck driving the tubes with pulsating unfiltered DC... If you do add a filter cap, you might want to insert a low-value (22 ohm, perhaps) in series with the one of the bridge lines to prevent a large current surge when first powering up. Also, make sure the capacitor is adequately rated for the job. You wouldn't need too much capacitance - 50 uF would be sufficient, but it must be at least a 250V rated unit. This brings up another point: with the circuit shown and the addition of a filter capacitor, the output voltage available will be considerably more than the RMS value of the input voltage - theoretically 1.414 times the input, but in practice under load closer to 1.3. This means that if the incoming line is a bit high - say 120 instead of the nominal 117, the voltage at your capacitor will be somewhere between 155 and 170 volts - still OK for this application, but unwise to forget about. ~~ Mark Moulding On Thursday, March 22, 2018 at 5:23:24 AM UTC-7, John Murphy wrote: > > I am currently working on a very similar project. Here is what I've > learned: > > 1. The IN-9 tubes don't all act properly using a 150V DC switching power > supply (I bought several different models from eBay). The glow of the tube > becomes disconnected from the bottom and "floats" in the middle - this is > not how a bargraph should behave. I have been successful using a full wave > rectifier circuit from 120V mains through a 1:1 isolation power supply > (US). If you have 240V mains, you would need a 2:1 step-down transformer. > I used the KBP307 rectifier instead of discrete diodes. Do NOT try to use > the rectified mains without a transformer. In addition to this being > dangerous, if the DC 0V has a path to earth ground, the rectifier will be > destroyed, and also likely take out other components like the uC. I am > using a Triad VPS230-110 as it's fairly inexpensive. It has a maximum > output current of 220 mA, but for a music visualizer, you won't have full > scale output on all the tubes at the same time - you could enforce this > using code in the microcontroller if you're worried about it. > > 2. Most microcontrollers have a limited number of pins that you can output > PWM on. If you want to drive 16 tubes, you need 16 PWM (or analog out) > pins. I am using two serial octal DACs (LTC1665) to drive the base of the > MJE340 transistors using the circuit in the paper you referenced. DAC > values are set with a synchronous serial stream. The clock and data lines > are common to both DACs and each one gets its own chip select for a total > of 4 digital pins needed to drive 16 tubes. > > 3. If you buy New Old Stock (NOS) tubes, some of them won't initially glow > to full height due to being in storage for so long. They need to be > "burned in" - something about the physics of the cathode tube that I don't > really understand. I have found that driving them at 15mA for about an > hour has been enough. Over that time the glow gradually creeps from about > 1/2 scale to full scale. After that, they all have worked to full scale. > > Have fun! > > > > > > On Wednesday, March 21, 2018 at 3:52:45 PM UTC-4, Mikołaj Walkowiak wrote: >> >> Hello everyone! I'm doing project for college and I've decided to make an >> audio visualiser using IN-9's. The problem is I don't have any idea how to >> power them. I'd like to have 18 tubes for different sound frequenties and >> I'll be using stm34 to calculate the value each tube should show.. >> >> Now, I know I need 140v and 0 - ~~12 mA for 1 tube but that's all I know >> honestly. I think I'll use something like the 0-offset driver found in >> HERE <https://www.die-wuestens.de/rd/IN9-2.pdf> controled by PWM of my >> uC but I honestly have no idea how to power them. Is 140V(or 150V? >> everywhere except there it says 140V) enough even for 18 tubes? If yes is >> it possible to make this kind of supply myself as I can't find anything >> reasonable price-wise with 140V. Do I need to consider anything else? >> > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/5d46470d-1748-42d3-8707-19d60cdf1b04%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
