Nixie Thermometer / Hygrometer

Tubes, sensors and a micro in a single design

Nixie Thermometer / Hygrometer

Measuring temperature and humidity with a modern sensor and displaying the values on a retro display — it’s all described in this article. A calibrated, ‘digital’ sensor provides data via its I2C interface to a microcontroller driving four Nixie tubes and automatically alternating between temperature and humidity, while providing a nice fading effect. It’s a must-have!

Component list

Resistors

R1-R4 = 22kOhm

R5,R11,R12 = 10kOhm

R7 = 47kOhm

R8 = not used

R9 = 820kOhm

R10 = 330(

R13 = 5.6kOhm

R14 = 470kOhm

R15 = 4.7kOhm

R16 = 150(

Capacitors

C1-C4 = 100pF 2000V, 10%, radial, 5mm pitch (Farnell #1141797)

C5-C8,C11,C12,C16-C18 = 100nF 50V, 20%, pitch 5mm

C9, C10 = 33pF 100V, 5%, 2.54mm pitch

C13 = 10μF 250V, 20%, radial, 5mm pitch

C14,C15 = 100μF 25V, 20%, radial, 2.5mm pitch

C19 = 470pF, 100V, 10%, 5mm pitch

Inductors

L1 = 330μH 1A, 20%, axial, D×L = 11×32.5 mm (0.43”×1.28”) max.

Semiconductors

D1 = BYV26

D2-D4 = 1N4001

IC1-IC4 = 74141 or K155ID1 (?155??1)

IC5 = PIC16F876-20/SP

IC6 = 7805

IC7 = MC34063

IC8 = SHT21 I2C humidity and temperature sensor [1] (Farnell #1855468)

T1,T2 = MPSA42

T3 = IRF820

Miscellaneous

X1 = 6MHz quartz crystal

V1 = IN-19A, Nixie Tube (symbols)

V2-V4 = IN-14, Nixie Tube (numeric)

K1 = 2-way PCB terminal block, 5mm pitch

PCB # 110321-1

As you can see from the following pictures, the project progressed nicely…

This picture shows the top view, without the last tube, which I was waiting for

Most of the components are very easy to solder on. The Nixie tubes are very hard to get into the holes, but I managed it so anyone should be able to do it! However, the Sensirion SHT21 chip is 3mm x 3mm and is ridiculously hard to get on – this needs specialist attention and a steady hand. You can see the sensor in place in the picture below. Be sure to read the data sheet correctly, and don’t solder it on the wrong way (I *may* have done this!)

The tubes eventually turned up – I was more excited than I probably should have been ??

Finally the final tube came and was soldered into place – a really lovely display. The sensor has to be at least 15cms from the circuit board, otherwise you get spurious results from the heat of the components on the board

I built this case to house it, Im very very pleased with it