20 A 85 V Self-contained DC power meter - Improvements

In this video, I show you the improvements to my DC power meter. In the previous video, I showed all the functionalities of the power meter and I presented the code written to operate the screen and communicate with the INA238 power meter IC. In this video, I present the power meter with 3 different displays, 2 OLED and 1 LCD units.

Additional resources

The new version (v 1.1) of the board contains a small “bug fix”. I accidentally left the address pins of the INA238 floating in the first version (v 1.0). It was not a big deal to fix it manually, but I wanted to publish a board without this issue, so people have no issues replicating my project. The address is permanently set to “10000000” by pulling both A0 and A1 pins to the ground (see Table 7-2 in the datasheet). Actually, this address does not matter as long as it is set because we only use one INA238 chip with the microcontroller anyway. But the address must be set and the pins cannot float.

I also received the LCD that I originally wanted to use with this board, so I could finally assemble the board with it. I also needed to write a new code for the LCD. The new code is, of course, explained in the video. Furthermore, I tested the board with a larger, 1.3” OLED display. It works well, however, I noticed a small glitch on the display and I don’t know if it is the display or it is the code. This needs a bit more inspection.

As you might notice, using the larger displays prohibit the user from adding binding post terminals to the board. If you need the binding post terminals, go for the 0.96” OLED. Just make sure that you purchase the one with the correct pin layout (VCC/GND/SCK/SDA). If you use the larger displays, you can attach fork or ring terminals to the board using an M4 bolt, a washer and a nut. If you want to make a permanent connection, this is anyway the best way in my opinion. Or, you can use alligator clips with the M4 bolts, in the same way I did in the 3rd picture in the gallery.

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Power meter with 3 different displays

All of them are 128x64 pixel resolution displays. Left and middle are 0.96” and 1.3” OLED displays and the right one is an LCD.

Three power meters

Three power meters in action

They are connected in series. The power supply feeds the left power meter which is then connected to the middle in series and so on… Notice the voltage drop between the units!

Old PCB

Pin 1 and 2 (address pins) were accidentally left floating (NC; no connect) in the previous version. I fixed it by connecting them to the nearest GND using a tiny copper wire.

New PCB

The previous error is fixed. Pin 1 and 2 are connected together on the board and then they are both connected to ground.