UNI-T UT61E Backlight, Part 3

All that's left is the sense pad. Which means I need to figure out an appropriate size. I'm using a brass strip that's 1/2" wide by 1/64" thick because it's easy to solder and bend. I know the meter's case isn't the thinnest so I'll use some polycarbonate (.24" thick) for testing different sizes. The main thing is I want a finger touch to turn the light on, not a finger passing nearby or a finger hunt.



My test board is soldered to a longish piece of wire and 2-1/4" long brass strip.



A 1" long strip works reliably, however a touch area that's too small could mean hunting to switch the light on.



I settled on a 1-1/4" long strip and it just so happens to fit nicely into the back cover.

 

Soldered in and covered in Kapton. I also wedged a little piece of foam by the buzzer to hold the sense wire in place. Time to put it back together.



Actually closing the meter wasn't tricky or difficult. The backlight is a little dimmer than the picture above but overall I'm very happy with the mod.

Since I have a second board, I put 9V on it and measured the current draw. The UNI-T measures about 10µA but measures a max peak of 30µA and min of 4µA. So something is going on but I don't have a scope to investigate further and I'm pretty content letting it be a mystery ... for now.

The last picture above shows 1.76V on the test board which still registers touches and lights the led! You do have to cycle the power between large voltage changes to allow the TTP-223 to re-calibrate. I'm really pleased with the TTP-223. It just works. It's not finicky or complicated to integrate which is perfect for my skill level.

To be continued ... maybe with battery tests ...