If you're like me, you may have a bunch of Lithium Ion cells either laying around waiting for the future projects, or already installed in a variety of equipment. It's easy to forget where they all are, and what state they're in. The purpose of this project is to create a simple and energy efficient device that is powered by the battery cells and reports its voltage over wifi without much drain over a long period of time. To accomplish that an ESP8266 microcontroller is programmed to remain in deep sleep and only report the voltage once a day.

This project was created using VSCode/PlatformIO.

See settings.h for wifi credentials and various other parameters.

The code will run on all ESP8266 boards, but to utilize the deep sleep WAKE pin has to be exposed and connected to RST. Thus the boards such as ESP-01 shouldn't be used. Pictured below is the ESP-12E.

Pinout:

CH_EN -> 10K -> VCC
RST -> GPIO16 (WAKE)
GPIO0 -> 10K -> VCC
GPIO15 -> 10K -> GND

Important! ESP8266 can't accept more than 3.6V directly, a cell charged above 50% would damage it. For such reason VCC should be connected via a diode which will provide the necessary voltage drop. The code accounts for this drop in order to estimate the real cell voltage.

Example Python script is provided. The script has to run with root privileges in order to access MAC addresses of the source packets. Scapy Python library is used for parsing the packets.

sudo tcpdump -e -n -A -x ip and udp and port 1080
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eno1, link-type EN10MB (Ethernet), capture size 262144 bytes
21:03:09.728784 34:94:54:62:ad:b1 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 60: 192.168.1.75.53437 > 255.255.255.255.1080: UDP, length 8
        0x0000:  4500 0024 0003 0000 ff11 f9d2 c0a8 014b
        0x0010:  ffff ffff d0bd 0438 0010 f3d1 ff04 0000
        0x0020:  760e 0000 0000 0000 0000 0000 0000
21:03:10.008129 34:94:54:62:ad:b1 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 60: 192.168.1.75.53437 > 255.255.255.255.1080: UDP, length 8
        0x0000:  4500 0024 0004 0000 ff11 f9d1 c0a8 014b
        0x0010:  ffff ffff d0bd 0438 0010 f3d1 ff04 0000
        0x0020:  760e 0000 0000 0000 0000 0000 0000
21:03:10.394349 34:94:54:62:ad:b1 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 60: 192.168.1.75.53437 > 255.255.255.255.1080: UDP, length 8
        0x0000:  4500 0024 0005 0000 ff11 f9d0 c0a8 014b
        0x0010:  ffff ffff d0bd 0438 0010 f3d1 ff04 0000
        0x0020:  760e 0000 0000 0000 0000 0000 0000

sudo ./limon_receiver.py 
waiting for reports...
2023-10-29 21:03:09.731877 34:94:54:62:ad:b1/192.168.1.75 [Big Blue 80Ah Cell 01] volts: 3.70