I'm still experimenting with different techniques, but wanted to post an update. I picked up a 6volt transformer just to play with. I may not use it in an actual clock circuit, but I hooked up 3 IV-11 filaments in series and dropped a diode into the start of the circuit. I powered the grid/anodes off my 26VAC transformer. It worked like a charm and I got all three VFDs lit! I had the misfortune of reaching over a filament on the breadboard to get to an anode when checking voltage with my multimeter and instantly blew out one side of the filament when 28+volts got applied to it, so I've destroyed my first VFD tube ;). The two transformer solution is not ideal in practice for a clock, but at least I'm able to get these babies lit easily on a breadboard. I wish I had gotten into this hobby when LM9022s were still around!
I'll continue to provide updates on my modest experiments for those interested. I can't express how pleasing it is to simply get three of these tubes to light up on a breadboard! Simple pleasures for simple minds. I also have a question that is going to reflect my lack of knowledge with actual electronics circuits. I had to connect the last of my filaments (what I will call ground) to one of the leads from the second transformer (25VAC secondary - the line on this transformer not going to the anodes/grid) to close the circuit and get things to light up. If I wanted to keep the two power sources separate when I actually design my clock (i.e. 25V-60VDC to the grid/anodes) and 1.5VAC to each filament, how would I close the loop on the DC side? Can I keep the power circuits separate with one for the filaments and one for the grid/anodes somehow or do I have to close the loop so that both of them are together. Hopefully my question makes sense. Thanks, Dylan On Mon, Jan 16, 2012 at 5:18 PM, John Rehwinkel <[email protected]> wrote: > > In terms of the capacitors, is there a type you recommend if I am going > to go the capacitive reactance route to step down the AC? Besides using a > non-polarized one, is there any material that is preferable to others? If > so, any particular recommendations from online sources? > > Since you'll probably be looking for more than ten microfarads, your best > bet is aluminum electrolytic capacitors. These are made in non polarized > versions, which is what you want. You'll want a voltage rating at least as > much as the peak voltage from your transformer. A 24VAC transformer would > give 33.6 volts peak*, so a 35 volt capacitor would just barely > be adequate - I'd use a 50 or 63 volt unit. They're available from lots > of vendors, such as Mouser and Digikey in the United States. > > > I looked over the Kosbo circuit diagram and the datasheet. I gather I > feed a square wave into pins 2&4 of the MAX628 and connect 5&7 to the > filament? > > Right. The MAX628 contains two buffers, one inverting and one > non-inverting. So if you feed the same square wave to both inputs (pins 2 > and 4), you'll get opposite-phase square waves out of the two outputs (pins > 5 and 7). That way, one end of the filament will be at the supply voltage > while the other is at ground, then they'll swap, so on average the filament > won't see a voltage gradient. With this lashup, you don't need the > capacitors, but you may need a resistor if your supply voltage is greater > than the filament voltage (this is common). Even better, the filament will > have an average voltage of half the supply voltage, so if you turn off > anodes and grids by pulling them to ground, they'll be negative with > respect to the filament, which will give a good solid turn-off. > > If you pull up the data sheet for the LM9022 VFD filament driver chip, > there's a nice circuit diagram and description of how this works. > > http://www.ti.com/lit/ds/symlink/lm9022.pdf > > We'd just use the LM9022, but it is no longer made, which is why the Kosbo > circuit creatively uses what is intended to be a MOSFET driver chip to do > essentially the same thing. Notice also that the LM9022 data sheet shows > how to make the filament driver do double duty by adding a voltage > multiplier to also provide the anode/grid voltage - nifty! I am planning > on trying this with the MAX628, but haven't gotten around to it yet. > > > This is all still pretty new to me, and although I know what a square > wave is, especially after playing around with CMOS and 555 based > noisemakers, could someone spell out in detail how I would use the MAX628 > with let's say a 5V DC input and either a PIC/Arduino or 555 to get AC out? > > Note, if you try this with a PIC, AVR, or Arduino, it's easiest to just > use a PWM command to get a signal out, instead of doing it programatically > by setting an output high and low over and over (that works too, but it's > unnecessarily complicated). > > * An aside about AC voltages - the voltage out of a 24VAC transformer is > about 67 volts peak to peak, which can surprise folks who aren't aware of > it. It's easy to whomp up a power supply with a couple of diodes and > capacitors and come up with enough voltage to mildly overstress a 63V > capacitor with a transformer delivering "only" 24VAC. If a transformer is > lightly loaded, it can deliver more than its rated voltage, so you can > easily come up with 80 volts. > > - John > > -- > 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. > > -- 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.
