There have been several changes since I've posted my Rev1 CoinCell board her but this is the final version. This ESP32 project has an accelerometer, 0.69" OLED display, RGB led, temperature/humidity sensor, LiPo battery protection and dual capacitive touch sensors all powered by a rechargeable LIR2450 coin cell. It was not made for any specific purpose and was really more of a design challenge to try and make it as small as possible. It can be powered off of a battery or USB cable. If a battery is inserted and USB cable is plugged in, it will charge the battery and power the board at the same time. The design files and parts list are provided if you would like to assemble your own. Each board is hand assembled using a soldering iron and hot air wand.
As expected battery life is very, very poor. Current draw awake with the ESP connected to wifi, the oled, accelerometer and temp/humidity sensor on is around 85mA and only lasts around 5 minutes. In sleep mode it draws around 30uA and has been waking every 10 minutes to grab the time over wifi and display it on the screen. So far tests have shown that it will last around 12 hours.
Revision 1 started off at 200uA in sleep mode with efforts to try and get this down including different power supplies, software and hardware changes to the accelerometer but they have all ended in fail. Revision 4 now uses with a much better LDO and powering the accelerometer off of the ESP32 has finally got the sleep current down to a more reasonable 30uA.
Hardware design instead of software is my preference so at this state the only lame Arduino sketches are available that test out the hardware.
Note that shipping restrictions prevent me from shipping the LIR2450 battery One can be purchased Here
Revision 4 changes include:- a temperature/humidity sensor
- clearer silkscreen text was added on the bottom side showing what the user available nets are called
- two capacitive touch sensors on the topside act as buttons
- a LiPo protection part prevents a short circuit, over charge and under charge
- a microJST connector allows for a larger battery to be used
- the accelerometer is now powered off of a GPIO pin
When you purchase this project you get one assembled and tested board with coincell holder soldered in place along with a microJST cable.
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