28 October 2016

Easy socket for ZM1001 (and ZM1000 if necessary)

At HAM Radio Messe 2016 I bought a board from Philips PM2421 meter. It mounts 4x ZM1000 numeric nixies and 1x ZM1001 symbol nixie (+, -, ~, X, Y, Z). I tried to reuse the existing circuitry, especially to take advantage of the sockets on board, but there are limitations too: the thousands nixie has been wired only to show 0 or 1 (good for a 12-hour clock) and interfacing to the existing digital logic is not straightforward. On the other hand I could cut traces and feed data to the buffer or to the driver, but then I would have a large board behind the display ... for nothing!

Further down the conversion road I decided to unplug the symbol nixie, that would not be used in a clock anyway. Plan was to try to unsolder its socket, but the dense pinout looks familiar. A quick check at the datasheet reveals that those pins are 2.54 mm apart (or 0.1" if you prefer). Moreover the ZM1001 has only 6 symbols + the anode, so a "modern" socket can be built out of few female headers on a breadboard or custom PCB.

Here's a possible layout (bottom view):

There are no overlapping (red) lines and, if the homebrew socket does not bring unused pins to the board, a simple veroboard can be used:

Veroboard view of the homemade partial socket.
Mind that ZM1001 has two Anode pins, but just one grid, so using just one is fine. At least it looks so, and the datasheet does not suggest against it.

The tube sits well in the socket and has headroom so that pins are not stressed.
So, socket completed. The trick is that unused pins stay floating in the air and are not connected to anything, so routing without a PCB is simplified. The circuit above made with veroboard has copper strips running along its longest side and required very few cuts and jumpers to make it work with the 7441. Also, thanks to the fact that only 6 symbols are used, I can use 7441 outputs all on the same side.

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