UNI-T UT61E Auto Power Off, Part 3

It's tested and functional. I tested with just an IR LED hooked up to a power supply and the meter enabled and disabled the auto power off feature.

On the serial cable, I placed a jumper between pin 2 on the d-sub connector and R2 (red box). A 10k resistor was also put down (purple box). Oh yeah, and the IR emitter too (orange circle).

Again, all circuit diagrams used can be found here. Thanks Mr. Herbert!

To-Do's

-test serial cable

BOM

1x of LiteOn LTR-4206E phototransistor ... 3mm ... Digi-Key 160-1030-ND.
1x of LiteOn LTR-4206 IR Emitter ... 3mm ... Digi-Key 160-1988-ND
1x of 100k ohm resistor ... 0805 ... Digi-Key 311-100KCRCT-ND.

1x of 10k ohm resistor ... 0805 ... Digi-Key 311-10.0KCRCT-ND.
1x "UNI-T UT61E Auto Power Off v0.1" circuit board from OSHPark.
30 AWG wire similar to Digi_key K395-ND. 

UNI-T UT61E Auto Power Off, Part 2

I've been procrastinating a little because opening the meter means dealing with thin, delicate wires from the backlight mod.

With the meter splayed open, I located the trace that needed cutting. The IC is a CyrusTek ES51922 and the pin that needs isolating is pin 111 - RS232. It's the 9th pin down from the "top". The cut is highlighted with the blue line.

The jumper wire is then soldered to that pin and routes through the circled via to the "P" solder pad on my APO board. It's labeled "P" for some reason I've since forgotten about.

Placing the APO board - The IR windows on the case have a center to center spacing of about .65in (16.5mm). A little hot melt tacks it in place.

Power and ground were then routed around very carefully around that big hole, over the trimmer thingies and past the after-thought capacitor. After I did this, I realized I could have used much shorter wires and solder to the nearby caps for power and ground. A bit of heatshrink shrouds the receiver to avoid possible interference.

A bit more hot melt and it was ready to close up and test.

After assembling the meter and powering on, the PC icon was gone and a new timer icon showed up. At this point, my backlight mod stopped working and the meter was opened up again to investigate. Yup, a thin wire had broken off the backlight board. This has been fun but I think in the future I'm going to keep my meter in its stock condition :)

Continued in Part 3.