I started this project because I was tired of my fatshark beeping and shutting down at 3.6 volts. I am using a 2s 18650 3500mAh pack. This means my batteries are still almost half full when this happens. I first just used a 9v stepup to boost the voltage, but then tracking the battery level was a pain. Then I came up with this solution.
It not only lets you use your 18650 batteries up to 3v (per cell), it also adds voltage monitoring with adjustable alarms and a power on/off switch. On top of that the fan cable is now tidy and nice and the complete unit remains on the goggles the whole time while the battery is sitting in the pocket or on the belt.
The battery case has also a basic battery indicator - it gives a pretty good orientation of the battery state without hooking the battery up.
Printed Case
See 3D files directory
or order it here:
https://www.shapeways.com/product/Y7TP35MAT/powerpuck-case-front
https://www.shapeways.com/product/XVMKZEAJ4/powerpuck-case-back
Order the PCB on jlcpcb.com (1mm thickness)
See "PCB Files > Final Gerber" directory
ATMEGA382 AU
Y1: Xtal 16MHZ TXC 7A-16.000MAAJ-T
C1: 0,1uF cap 0603
C5: 100nF cap 0603
C3, C4: 18pF cap 0603 (2x)
10K 0603 Resistor
R3-R6: 330Ohm 0603 Resistor (4x)
D2-D4: GREEN LED 1206 (3x)
D1: 1x RED LED 1206
R1: 18K Resistor 1206
R2: 4,7K Resistor 1206
C6, C7: 10uF Cap 1206 (2x)
D6: Diode S1A
Pololu 9V Step-Up Voltage Regulator U3V12F9
Pololu Mini Pushbutton Power Switch SV
JST-SH Socket 6pin
9mm active Buzzer
8mm tact button
AMASS XT30 female plug
AMS1117/LM1117 regulator
Epoxy
ISCP USB Programmer like
https://de.aliexpress.com/item/5-v-Micro-USB-Tiny-AVR-ISP-ATtiny44-USBTinyISP-Programmierer-Modul-F-r-Bootloader-ISP-Mikrocontroller/32925343387.html?spm=a2g0s.9042311.0.0.725e4c4dZq4br5
Printed Case
See 3D files directory
2S Power-Indicator
https://www.banggood.com/2S-3S-4S-5S-Lipo-Battery-Voltage-Display-Indicator-Board-Polymer-Power-Indicator-Panel-p-1095698.html?p=03160313547712015036
XT30 connectors
https://www.banggood.com/de/Tarot-RC-Helicopter-Part-Amass-One-Pair-XT30-Non-slip-Plugs-TL2918-p-954269.html?p=03160313547712015036
2S Balance plug
https://www.banggood.com/de/Lipo-Battery-Balance-Charging-Extension-Wire-Cable-20cm-2S-3S-4S-6S-p-951866.html?p=03160313547712015036
Epoxy
