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Panel Meters

Being able to monitor current or voltage on an electronic project is really nice to have. There are lots of different panel meters available from the "usual suspects" online sites. They are fairly inexpensive - $5-10. And they are surprisingly accurate. Though, there are drawbacks. It is not always clear how you wire them up - often the instructions are vague or just plain missing. In addition, the wiring to connect them into your system can be messy. While it is only 4 or 5 wires, I would wind up having to splice the wires to the power supply and load. Looking at it later, the wiring was completely non-obvious and I would have look up the instructions, if I had them.

To solve this problem, decided to make a simple circuit board to tidy the wires up and document the connections. The panel meters I have used all have these snap connectors on the back. Correctly located slots on a PCB would allow it to be mounted on the back of meter making for a fairly clean solution to the wiring mess problem.

A recent project was a test and debug station for my CNC Breakout board. It is powered via USB and I wanted to know how much current it was drawing. I found something advertised as a 5 digit ammeter in the standard panel meter format. It cost me about $13 with 2 day delivery and tax. You can find them cheaper if you are willing to wait longer. It displays 4 digits to the right of the decimal point for 100 microampere (µA) "accuracy". Surprisingly, it agrees with my DMM, usually within 100 µA.

The backpack board takes a microUSB cable for the input and a standard USB A connector for the output. It snaps onto the back of the meter, making for a clean wiring solution. It passes the USB signals just fine. I was able to connect the PC to my breakout board and use a number of different programs that communicate with it. I can even download firmware to the breakout board (which has a Teensy 4.1 on it). I use the meter to help characterize the power draw of various features and once caught a short circuit. I also added a couple of output power connectors to the board to allow it to be used as a +5V supply for other projects. I probably should have shorten the wires before soldering.

I made an OSHPark project so you can order 3 boards (about $13) and have shared the Kicad design files. You can find them here.

In addition to the panel ammeter, you can find Volt and Amp meters in the same format. I created a backpack for this too. It uses either a barrel jack or screw terminal for input and a screw terminal for output. It also allows you to power the meter from the monitored voltage or from a separate power supply for monitoring voltage above 30V. The silk screened legend makes it clear how to connect the panel meter. I've made a shared OSHPark project and Kicad files available. You can find them here. And, yes, I should have shortened those wires too.


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