NixieTherm Kit

This is a novel electronic thermometer with a linear display looking just like a real glass thermometer, but based on nixie tube technology dating back to the sixties and seventies. It came from here:

I spent an afternoon building this kit whilst S&G were out on Saturday. Overall I think it was a great success and a fine kit with good instructions. Started by laying out the various packages from the box and inspecting the bits and pieces.

These are the packs of bits for the nixietherm kit

NixieTherm components

Accompanied by a pretty good set of instructions I then proceeded to mount all the PCB components, sticking to the recommended order which made pretty reasonable sense (resistors, capacitors…. and so on). All the components fitted just fine – no “fine tuning” required. The PCB is through plated, and although some of the pads were small, with a suitable iron posed no issues. I used a very fine lead solder which worked well. [Not yet experienced lead free solder so I don’t know how much more difficult it might be, although having read around the subject a bit I don’t expect it’s as bad as I imagine.] Once all the parts were mounted there were a number of test voltage measurements to make and a crude calibration was completed. Completed PCB for the nixietherm
The next stage was to burn-in the display tube. These Russian made components have been sitting in a warehouse for probably over twenty years. The result is that the linear display doesn’t light up all the way along the tube at first use. This is fixed by running the tube for an hour or so at a slightly higher than normal current. There are some pads to jumper on the PCB to set this up, and after then removing the op-amp the burn-in commenced. After about an hour and a quarter I couldn’t detect any improvement in the display’s range so that task was done.

Burn-in phase of nixietherm construction

Burn-in phase of Nixietherm construction

So after the burn-in was completed the next steps are to remove the burn-in jumpers and commence mechanical construction. The thermometer is housed in a neat case made of laser-cut perspex sections, and the display tube itself is supported in a cut-out section of perspex so as to resemble a conventional glass/mercury thermometer.

The first stage was to mount the vertical section for the display tube, upside-down, in a vice (or in my case, a large G-clamp to simulate a vice). Slide the tube into the cut-out with a couple of perspex supports, and then you continue to build the case from the top down. Some care required to make sure the bits will end the right way up and facing forward. All the mechanicals were in the kit – nuts, bolts, washers, spacers etc – and this was a fairly straightforward set of steps to work on. The final result when removed from the supporting “vice” was very pleasant.

The Nixietherm was left running overnight before re-calibration in the morning and a subsequent trimming later in the day so as to end up with a good looking and effective desk thermometer.

Finished Nixietherm

Finished Nixietherm

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