Compared to the thing:797733 the following was added:
- Li-Ion battery with charger and step-up modules;
- Banana sockets for connecting probes.
The OpenSCAD code was reorganized a bit to make adding other things easier:
- I use a center between PCB mounting holes as a reference point, instead of the center of LCD. Looks like my LCD is of the other model, and is a bit off, but the mounting holes are at their place anyway.
pcblx - extra space on left hand side, for additional components like banana sockets.
- Some tweaks to allow adding components.
Printed with 0.5 nozzle and 0.4 layer height for speed.
- T4 LCR/transistor tester - I had version marked QS2015-T4;
- TP4056 Li-Ion charging module - I had one marked O3962A, if you have the other version You may need to change module dimensions and LED positions in
- MT3608 step-up module;
- 470 or 330 Ohm 0805 SMD resistor for LCD backlight;
- 6.8 KOhm 0805 SMD resistor to set TP4056 charging current;
- Prismatic Li-Ion battery. I used a battery from old mobile phone. The battery compartment size is 60x34x8mm, if your battery exceedes that, You may need to change dimentions defined in the
prism variable in
- Some wire to make connections
- 4 x M3x16 flat head screws.
Most of this stuff can be found on Aliexpress or Ebay.
Also You will need the following tools:
- AVR programmer to flash new firmware - I used cheap USBasp programmer from Aliexpress;
- Some hookup wire, see here for ISP pinout and hookup example.
- Soldering tools
The following pictures show schematic and PCB changes needed to support Li-Ion battery power.
Changing battery charging current
Usually TP4056 modules come preset to 1A battery charge current which is too much for 800 mAh battery I used. To reduce it to match Your battery You will need to change the resistor connected between pins 2 and 3 of the TP4056 (R3 on O3962A module). I used 6.8k resistor, which gave me a charge current of about 175 mA. The formula for the charge current:
Ibat = 1200 / Rprog
New firmware should be flashed to the tester to support Li-Ion battery voltage monitoring. With stock firmware tester will think that battery voltage is too low for operation and will shut down.
I put the needed files here and the procedure is described here. To connect the programmer to the T4 ISP pins you may use the trick with 3x2 pin header.
Be careful to not to short anything in the process!
- Solder battery to B+ and B- pins on the charger module
- Check charging by connecting charger module to the USB
- Solder charger B- pin to step-up VIN- pin
- Temporarily connect step-up VIN+ pin to charger B+ pin
- Using multimeter and small screwdriver tune the voltage on the step-up VOUT+ and VOUT- pins to ~7V
- Disconnect step-up VIN+ pin from charger B+ pin
- Put all components in the case
- Connect all the needed pins to the T4 board as shown in the above picture. Note that discharge protection on the charger module is not used since mobile phone battery already has one inside.
You may use two pieces of transparent 1.75 mm filament as a charger LED light conductors.