Random Thoughts - June 7th 2020: Got a Fluke multimeter!

Recently I attempted to hand-wind a 400V high voltage transformer for my latest project, a NodeMCU/ESP8266-enabled Geiger counter I’m calling ‘Project Gizmo’. Unfortunately, my tests with the completed transformer were an epic fail, the transformer only managed to output about 310V, and on top of that it killed my beloved DMiotech multimeter!

DMiotech Smart-C multimeter

I was happily measuring the voltage on the AC range when I heard a “Fzzzt”, followed by the unmistakable smell of ‘magic smoke’, my multimeter no longer able to measure any voltage on either DC or AC ranges, though it still works with current and resistance.

So, I went on Amazon and settled on buying my first Fluke - a Fluke 115! It cost £197, and is so far the most expensive thing I’ve bought for my electronics hobby. I’m still putting off buying an oscilloscope, but I know I need one badly, it just costs so much and I hate spending money.

Fluke 115 multimeter

Fluke 115 multimeter with test leads

It has everything I need in a meter, AC/DC voltage and current, continuity/diode, resistance, capacitance, frequency… the only thing it doesn’t have (which I’ve only just realised) is duty cycle! My £5 ultra-cheap clamp meter has duty cycle, why not my Fluke, it’s so annoying! I’m wondering if I’ve accidentally bought an electrician’s multimeter, there is a difference.

Anyway, I’m now using a PCB mount transformer with a voltage multiplier to generate the necessary 400V to power my STS-5 Geiger Muller tube, I’m just waiting on some 1KV ceramic capacitors and I should be good to test the circuit! It’ll be exciting to actually hear those clicks of radiation for the first time!

Project Gizmo 1.1 schematic

My next task is to put the project together on a protoboard which I think will involve drilling out isolation slots to ensure a safe distance between the low and high voltage sections.

I’m also planning on making a CD4026-based 7 segment counter display for the Geiger counter prototype, wondering whether to make it on protoboard or just a breadoard. It’ll be cool to see an actual count of the radioactive pulses as well as hearing them.

Project Gizmo readout schematic