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)