Silent Q

Posted By azog on June 24, 2010

I purchased two of these off eBay, for what I considered is a “reasonable” price. As-is, untested:

Basically five nixie displays and five 7447 in a nice carrier. It just took a little while to beep out the pins, and then I drew this up:

Relatively simple: a Mega32 with a DS32KHZ TCXO. The HV converted is smack in the middle, it takes 12vdc and turns it into 180vdc.

Once I had this together, I inserted the nixie carrier, and realized that “untested, as-is” can be risky. But they were cheap enough, and really, that’s why I purchased two of them.

Some testing revealed at least one bad 7447, so I thought to be smart, and just replace them all with socketed 74141s.

But this is an old carrier board, and even though the PCB is double-sided, none of the thru-holes are plated. So the soldering was done on both sides of the 7447, which also meant it was impossible for me to solder the top-side due to the socket.

Luckily for me, I only tried the first 74141 in a socket, because previous experience has shown me for tasks like this, you be very conservative, and test every step of the way.

Out comes the socket, and solder the 7414 into the board.  However, things being as they are, once I had gotten to pulling the third 7447, I had lifted up several lands. Some were “unnecessary”, but some required the application of jumper wires.

At this point, I got pretty frustrated and put the whole thing down. I mean, I got a board for a reason, so I would haven’t to do point-to-point wiring; I might as well just have done this on perfboard.

So I figured, why not just replicate the carrier board? It is handy:

This turned out a lot better. I used BatchPCB, and whoever their fabhouse is, they’ve always produced good quality boards. It did take quite a bit of finagling to solder the leads from the tubes into the board, but eventually everything went well. I was able to go back to my original plan of using socketed 74141s.

Thing is, this is a pretty generic carrier. The nixie leads just wire up into a 6×2 header. All you have to arrange the leads. I didn’t label anything on the board, because I originally considered this just a one-off, but I might go back, relabel everything, and use wider spaced holes for the nixie leads.

This is direct drive, not multiplexed, so it needs at least 2 full PORTs. There is a fifth tube on there, which is wired to the “leftover” bits where the DS32KHZ and INTx buttons attach.

For power, I am using a triple-output switched wall-wart. I found them on Jameco or Digikey for a few dollars. It came with +5vdc, +12vdc, and either -5vdc or -12vdc, which I did not care about.

Again, being conservative, you always test. While trying to determine which was +5vdc, I found that this was wired for black to be +5vdc, red was ground. Luckily, everything inside the wallwart was labeled on it’s own PCB, so I just removed the negative voltage, and wired red to +5vdc, yellow to +12vdc and black to gnd. No need for pictures :p

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