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LoRaWAN Battery Monitor

From MakerVan Labs

     
LoRaWAN Battery Monitor

Release status: experimental [box doku]

Description LiPo battery monitor to regularly check cell voltages
Last Version  0.1 (2021-01-03)
Platform  ATMega328
License  CC BY-SA 4.0

The LoRaWAN Battery Monitor is a LoRaWAN connected device based on the ATMega328 LoRaWAN Node to automatically measure the individual cell voltages of a Lithium Ion battery pack (up to 7S)

Parts

Note: Antenna and LoRaWAN module are dependent on the local frequency band used for LoRaWAN. The selected items are meant for 868Mhz, which is the frequency band for Europe

Part Partnumber Amount Source Notes
PCB LoRaWAN Battery Monitor PCB v0.1 1 -
Microcontroller ATMega 328P-PU 1 Reichelt
IC socket 28pin 1 Reichelt
Quartz 8Mhz, HC49U-S 1 Reichelt
Resistor R4: 10k 0805 1 Reichelt
Capacitors C4, C5: 22pF 2 Reichelt
C6, C7: 100nF 2 Reichelt
Reset button SW1 1 Reichelt
Measurement
Resistor R5: 10k 0805 1 Reichelt
R6: 33k 0805 1 Reichelt
R7: 75k 0805 1 Reichelt
R8: 110k 0805 1 Reichelt
R9: 160k 0805 1 Reichelt
R10: 200k 0805 1 Reichelt
R11: 240k 0805 1 Reichelt
R12: 270k 0805 1 Reichelt
Multiplexer U4: 74HC 4051 (SO-16) 1 Reichelt
Voltage regulator for >3.3V input
Voltage Regulator U3: 3.3V, LDO, TO-92 -> LP2950-3.3 1 Reichelt
Capacitor C2, C3: 4,7µF Elko, >16V 2 Reichelt
LoRa Modem section
Antenna 868Mhz SMA 1 DigiKey
Amazon US
Amazon DE
AliExpress
Antenna Connector SMA Edge mount 1 DigiKey
Amazon US
Amazon DE
AliExpress
u.FL surface mount 1 DigiKey To connect an SMA antenna, you will need a matching pigtail
LoRa Module RFM95 868Mhz 1 DigiKey
Amazon US
Amazon DE
Input voltage measurement
MOSFET Q1: BSS 84 1 Reichelt
Resistors R1: 100k 0805 1 Reichelt
R2: 150k 0805 1 Reichelt max input voltage for this R2/R3 combination: 16V
R3: 10k 0805 1 Reichelt
Capacitor C1: 100nF 1 Reichelt
Connectors
ISP J1: 2x3, 2.54mm 1 Reihelt 2x4 connector is much cheaper than 2x3, but you can simply cut off one section
Pin headers P3, P5, P6, P9, P10 (many pins) Reichelt Just get one long row, and cut off those you need
Screw terminals (Power In) P2 (outer pins): 2 pole, 5.08mm 1 Reichelt only if using voltage regulator
Battery connector J2: 14pin 1 Reichelt

Notes

  • Splitting the voltage divider as I did didn't work out, due to the protection diodes and other circuitry within the 4051. There have to be full voltage dividers "in front" of the multiplexer, basically adding a 10kΩ resistor to ground on R6-R12. This leads to continuous power consumption. Scaling up the resistors should help though.
    • Recommendation on twitter was to use the BQ76930 chip by TI as an alternative. Looks very interesting, but I think I'll go with the voltage dividers for now. Power consumption shouldn't be that big of a deal in this case.

Links

License

  • Licensed under Creative Commons Attribution-ShareAlike 4.0 Unported License (CC BY-SA 4.0)