Some people have already implemented relay-based DACs (such as the sound card of TIM-8) so there is nothing groundbreaking here. However, since it's my first relay-analog converter, a log was important! I had shelved the galvanometer-hexadecimal-display in the last log, but I now have the voltmeter so I had to test it.

I chose a model with a wide display area and screws on the front so I can easily modify the display grades. It's lousy but it seems to work.

Then I tested the display against a known good source and it actually works well.

The resistance is measured with an ampmeter in series at 10V: 0.976mA, or R=10245 ohms. This gives an estimate of the required resistors in the R/2R ladder, the relative error and the power that it draws (hint: low).

I don't know exactly yet how I'll provide 16V (the galva uses 15V but the R/2R ladder drops 1V minimum) but several rails that can be combined, for example the difference between the +6.6V and the 24V rail is about 17V, a series potentiometer (5K ?) will adjust the needle. The differential supply will certainly fluctuate quite a lot and heavy filtering (regulation, capacitors and/or diodes ?) will be required...

The display is quite large and slow but cheap and easy to use so it is not suitable for the main display but can serve for auxiliary display...