Several people have asked me what parts I've used and how I've wired up the UT61E backlight mod with touch sensor I posted in a different topic so I thought I might as well dedicate a thread to the subject so it's easier to find for people searching for it.
If you want to use any of the pictures in this post then feel free to do so but please mention who and where you got them from. It has taken me quite an amount of time to come up with this so please have the courtesy to mention me and link to this thread.
https://youtu.be/EHStaKB0BwIWhile looking for a tutorial to install a backlight I came across a
post on diyaudio by user Tolik.
I loved the touch sensor but he built everything from scratch and there are quite a few components involved.
I don't really like the fact that when you let the UT61E's ES51922A chip control the backlight, it turns off again after 60 seconds. Besides that, his circuit uses around 35mA which I think is quite a lot (compared to what the meter itself uses).
So, I started looking around if I couldn't build something myself with less components and not connected to the ES51922A chip.
The result is a very simple circuit with only a few components.
It draws only a few micro amps when the backlight is off and a few milli amps when the backlight is on.
The output port sink current on the touch module is 8mA but I've tested with way higher values and it doesn't seem to damage anything.
The resistor used depends on the specs of the LEDs so the one in the tutorial is not correct.
This tutorial may look for dummies but that's because I'm a dummy myself when it comes to electronics. I only have very basic knowledge of it and build things by logical reasoning and learn a little as I go along.
Thanks to helpful member mariush in this thread and a member on Hackaday (who covered this mod on their blog), I have revised this mod which has drastically improved efficiency.
Parts list (click on link to be taken to item on eBay):
2x
3528 LED red1x
TTP223 touch sensor module1x
3.3V low quiescent current voltage regulator MCP1703T-3302E/DB1x resistor (value depends on LEDs used)
First off, modify the touch sensor module. We don't need the touch area because we're going to make our own. Bridging the W1 terminals (pins 5 & 6 of the TTP223 chip) turns the module from a momentary switch into a toggle switch:
![](https://image.ibb.co/d47g3R/TTP223_mod_800.jpg)
Your module should now look like this:
![](https://image.ibb.co/j4NQV6/TTP223_after_mod.jpg)
Since we've removed the LED (D1) there's room to put the voltage regulator on the board to keep things compact.
The middle leg of the voltage regulator can be removed since we're using the tab on the top.
The touch module has a capacitor on the input side so we can solder the MCP1703 regulator straight to the board.
![](https://image.ibb.co/c2cg3R/TTP223_MCP1703.jpg)
Left of the battery compartment is plenty of room to install the circuit.
Watch out for wires getting trapped between the battery compartment and board when you put the back of the meter back on.
The 9V we're using is the battery power which gets switched by the rotary selector so the circuit turns on and off when you turn the meter on and off.
I've used green color to draw the +9V signal because red on red isn't really clear to see
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
Again, note the resistor is NOT the correct value in this picture.
![](https://image.ibb.co/hFjiHm/def_detail.jpg)
To find the right value for the resistor it's handy to try out a few values or just use a variable resistor so you can set the brightness to your liking.
Keep the brightness as low as possible. The touch module isn't really made to supply more than 8mA of current although in real life it can handle at least twice that amount.
Solder a wire (I've used 30 awg wrapping wire for all wiring) to C3 on the edge of the board.
This wire runs to the top of the meter and connects to a piece of aluminum foil tape. If you're having difficulty soldering to the foil tape, just strip off a fair amount of insulation and use another piece if tape to attach the wire to the foil tape.
The larger the piece of foil tape, the more sensitive the sensor. If too large, the backlight will turn on even before your finger touches the meter. Experiment to find the correct size.
![](https://image.ibb.co/gz7g3R/def.jpg)
You can use the 2 holes seen in the picture to lead your LED wires to the other side of the board.
DO NOT SOLDER THEM ONTO THESE TERMINALS AND MAKE SURE THEY'RE PROPERLY INSULATED!
30 awg wrapping wire is perfect.
![](https://image.ibb.co/b3tXA6/Ledholes_text.jpg)
We're wiring the LEDs in parallel.
![](https://image.ibb.co/gMZuOR/Ledwiring.jpg)
Using a very tiny amount of hot glue, stick the LEDs onto the foil tape that's on the plastic plate behind the LCD display.
The cutouts are there, because Uni-T also uses these plates for the other 61x models that do have backlight already installed.
The LEDs should be emitting light into the plate (to the top of the picture).
![](https://image.ibb.co/hLCQV6/LEDs1.jpg)
And here's a view from the other side.
![](https://image.ibb.co/fnRkV6/LEDs2.jpg)
To make sure nothing's interfering with the meter I've wrapped the added circuit board in aluminum tape (without taking the backing off) and connected it to GND (VB-) so it's completely shielded.
When re-installing the board and cover, make sure no wires get trapped or damaged.
If you ruin your meter by installing this mod, don't blame me.
I can't be held responsible if anything gets damaged in the process.
Any comments, tips and annoyances are welcome
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)