README.md

Smart battery power monitor project

A slim circuit board for managing charge and discharge of multi-cell LiFePo4 battery packs. Intended to track state of charge by coulomb counting and prevent battery pack damage from over discharge, over current and over temperature conditions.

Goals:

1. Monitor and record total amperage in and out
2. Monitor and record temperature, ideally three places
3. Monitor and record pack voltage
4. Provide under-voltage disconnect
5. Provide over-temperature disconnect

Features:

1. Atmel AVR Micro: ATMEGA4808 TQFP-32
2. Hall effect current sensor: TMCS1108
   • Check my inventory for ACS7xx sensors!
3. FRAM data storage : I2C FM24C64B
4. Precision ADC: I2C NAU7802
5. Hot swap buffer: I2C TCA4311a, PCA9508
6. Host side i2c mux: PCA9545A
7. Max PCB width 18mm
8. Precision fixed resistor for thermistors?
   • Thermistors: NRL1504F3950B1F
   • Thermistors connect to uC ADC
9. Power selector IC: AP2411
10. Low Iq power supply for battery side, switching or linear?
11. SMT button for battiery status

Connectors:

1. Battery side
   • Battery In and Out (14 ga) - WAGO screw cage
   • 6-pin jst-xh vertical for three thermistors
2. Upstream interface: I2C
   • JST-xh 6-pin connector +5v, GND, SCL, GND, SDA, GND
   • TCA4311 on battery side
   • I2C switch on host side (might not need)

Indicators:

1. Bus controlled:
   • Bus power (from vcc)
   • Bus active (from CS line)
2. uC controlled:
   • Battery SOC (three leds)
   • Battery health (red/green)

Client Commands:

• See registers.md for addressing and more details

Questions:

1. Data logging without a RTC?

• Chip seems to keep time well enough with occasional updates from master

1. High side or low side disconnect?

Resources:

ATMega4808:

• https://www.digikey.com/en/products/detail/microchip-technology/ATMEGA4808-AUR/10444912
• https://ww1.microchip.com/downloads/en/DeviceDoc/ATmega4808-09-DataSheet-DS40002173C.pdf
• https://github.com/MCUdude/MegaCoreX#pinout

Thermistor:

• https://www.digikey.com/en/products/detail/eaton-electronics-division/NRL1504F3950B1F/15927588
• https://www.maximintegrated.com/en/design/technical-documents/app-notes/1/1753.html
• https://www.jameco.com/Jameco/workshop/TechTip/temperature-measurement-ntc-thermistors.html

Readng precise voltages:

• https://skillbank.co.uk/arduino/measure.htm

ATMEGA Arduino:

• https://github.com/MCUdude/MegaCoreX

AVR DA / DB / DD Series:

• https://github.com/SpenceKonde/DxCore

Bootloader:

• https://github.com/Optiboot/optiboot

FRAM:

• FM24C64B

Hall Effect Sensor:

• https://www.ti.com/product/TMCS1108

Hot swap buffers:

• https://www.digikey.com/en/products/detail/nxp-usa-inc/PCA9545AD-118/789953

• https://www.ti.com/product/TCA4311A?qgpn=tca4311a

Switching regulator (tiny):

• https://www.diodes.com/assets/Datasheets/AP62200_AP62201_AP62200T.pdf

ADC:

• https://www.nuvoton.com/export/resource-files/NAU7802%20Data%20Sheet%20V1.7.pdf