Voltmeter success!

Now that I’m back to where all my tools are, I had a few minutes to pop down and perform the changes I have been documenting.

After messing about with a few alligator leads, I determined that not only does IN LO need to be connected to analog common, but the voltmeter ground as well. When IN LO wasn’t grounded, I got an initial reading (with nothing connected to the input) way off zero, beyond the point the trimpot could calibrate it.

As the forum posts mentioned in my previous articles stated – the dotted connections. must both be connected for the thing to work properly. This means REF LO is connected to ANALOG COMMON which is connected to IN LO and then GROUND. Given the language in the datasheet, I would have that it was an either/or scenario, not both. Regardless, I am pleased it’s working.

The assembly process was a bit messy, I cleaned up a lot of solder blobs and accidental solder bridges. Unfortunately, I soldered/desoldered and overheated a couple of pads, removing them from the board, the result works but it’s messy. If it can survive a few knocks and keep working, good enough for now. I can always build another one.

The divider resistor values calculated in my previous post worked a charm. Rather than wasting money and time grabbing 1% resistors, I tried various combinations of 5% ones until I got very close to those values. I tried a number of test voltages from batteries and my soon-to-be-replaced power supply and noted that not only was the reading linear across a range of voltages, but along it’s scale ranges as well which is exactly what I was looking for. After calibrating to 100mV and further trimming it a hair to get it in line with my multimeter, I am pleased to say it seems accurate to better than 1% which is not only good enough for it’s intended purpose, but better than I expected.

I have earned myself a beer tonight!

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