Completion of the multimeter under 18650 battery + backlight with AUTO OFF

Long matured the idea to redo your multimeter under 18650 battery(battery “crown” went only so….). Finally, the day has come!

The first thing I did the backlight of the display. The screen of the multimeter is big enough and bright Sunny days or at dusk, the numbers are almost not readable, that I’m often annoyed.
For this modification, we will need to film from the sandwich matrix of the old broken monitor, for example 940n.

We need film-mirror. It will use as a substrate for reflective effect.
Cut the rectangle under the screen and everything is almost ready, it remains to glue the led into the end of the LCD screen of the multimeter. Is the most important part, because depending on the location and angle of inclination depends on the degree of fill of the matrix light.
Unfortunately, I have a picture of this step, but it is not difficult to repeat. Led, by the way, took out the backlight of the laptop, there is 30 pieces per tape. You can use led lights matrix of non-performing smartphone, they’re on 2B.

DT 890B+ has AUTO OFF feature that disconnects power to the multimeter, if you forgot to turn off using button on / off. According to my idea, I wanted to use this feature and to disable the backlight — turns off the movie and immediately turn off the backlight.

To implement this feature, I had to poke a multimeter in order to find the desired point on the chip LM358. The output is a standard 9-volt(or slightly less) for led backlight very much calculated the appropriate resistor was 0.6 K.

Next was to try the fee-charging Li-Ion in the future the box — drew a line deepening Dremel:

Fitting and final installation on double-sided tape with gluing:

The next step — Step Up) All on the same double-sided adhesive tape and is sealed with charge chrome the Board:

Sapaw to battery power wire to “step up”,

put 9 volts:

Drilled with “deuce” hole for the optical fiber and filled in a strip of glue.(I wanted to see the led of the battery):

Taped paper to isolate potentially dangerous places(though there is a gap between the cost of the movie and all that farm, but just in case, you know):

All collected and check for serviceability. Automatic power off function works perfectly in tandem with the backlight(in this model it is approximately 20 minutes of inactivity)

Check the guide light while charging:

And a fully charged battery:

And one final photo of the light in normal light:

The RESULTS:
The pros: For very little money, we get an almost “eternal” rechargeable multimeter with backlight.
Cons: Need to have a similar multimeter with large space to add a “farm” — people’s DT-830 this number is not likely to ride…
There is no possibility(yet) to disable the “step up”(instead ate at idle), but feels that he has very little in the “booth Bay”.
UPD: According to the scheme Prizrak Night and with his permission, added in the schema system “quench” STEP UP: replaced the capacitor and screwed the ENable wire from the “step up”(pre-lifting leg) to the output of the comparator with the multimeter:



Now, time off has become very comfortable for me — 3 minutes 50 seconds( recall that the time was 20 minutes, there was a capacitor on 47мкФ).
Now STEP UP when you disconnect the multimeter, also “extinguished”, thus saving battery power.
Remained most a little — to calibrate Ion the multimeter on the “step up”.