bigclive

Slightly shonky voltage probe (Patreon)

Published:

2023-03-24 23:14:32

Imported:

2023-03

Content

I promise, this is the last vehicular themed video for a while.

It's a low voltage probe with built in digital voltage meter, that could be used for many applications and not just automotive.

I get the feeling the circuitry may be based around either a dedicated meter chip, or a microcontroller mass programmed for this application. It's pleasingly minimalist, but astonishingly accurate. I tested it with a Fluke meter as a reference.

I reckon the mystery diode is to prevent the regulator being reverse biased by the tiny leakage current via the sense resistor network if the probe is applied to the wrong polarity.

https://www.youtube.com/watch?v=f7xBeN-wdj0

Files

Unusual, but accurate low voltage probe (with schematic)

A strange electrical probe from eBay, that may be aimed primarily at vehicle use, but probably has other applications. A side by side test with a Fluke meter showed an accuracy within 0.1V across the full range. The voltage range stated on the packaging is 3 to 36V, but I'd recommend 35V tops, and preferably lower due to the use of a standard 3.3V regulator. The circuitry is notable for the use of what I guess is tri-state multiplexing (charlieplexing) to drive the LED display, meaning that the three digits can be controlled by just six connections. The red lead is negative and the black probe is positive... So fortunately it does have polarity protection and an LED to indicate polarity. Strangely, green means wrong polarity and red means correct polarity. The only reason I can think of for the mystery diode between the input and output of the regulator is for the tiny current leakage via the sense resistor, that might reverse bias the voltage regulator if the probe was connected with the wrong polarity. The eBay listing this probe came from had the following description:- "12V Circuit Tester Probe 3-24v Electric Car Fuse Test Light Voltage Pen Detector" I paid £8 for mine inclusive of shipping. If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:- http://www.bigclive.com/coffee.htm This also keeps the channel independent of YouTube's algorithm quirks, allowing it to be a bit more dangerous and naughty. #ElectronicsCreators