Minimalist bike computer and hub dynamo power manager.

A typical hub dynamo can deliver approx. 6 - 10 V at 0.5 A. Output current is inductively limited and stays relatively stable over speed. However voltage will go up. A custom made buck converter is used to extract maximum power and charge a 18650 liion cell. The front and back bike lights will be powered by this cell.

Speed and distance is tracked by measuring the zero crossings of the hub dynamo AC output. Data is collected in the CPU until read out by a mobile device over bluetooth and possibly published to a cloud service.

• Will use ESP-WROOM-32 and make good use of the sleep modes
• AC input zero crossing --> falling edge interrupt. Wake up CPU and increment counting reg.
• Every second, keep track of:
  • Battery voltage. --> ADC + voltage divider to 3 V
  • Generator RMS(or peak) voltage. --> ADC + voltage divider to 3 V
  • Generator RMS current. --> 5 mOhm shunt + TS1101 + ADC 1 V
  • Battery current in and out --> 5 mOhm shunt + TS1101 + ADC 1 V
  • Realtime clock timestamp
• Store these datasets in a circular buffer in memory, until read out over BLE.
• Manage the Buck converter PWM to charge the battery with maximum current

• 3.3 V LDO
• WROOM-32
• Buck inductor
• Buck Schottky: STPS3L40UF
• High side mosfet driver: LTC4440-5 in SOT-23
• High side Mosfet: STL6N3LLH6
• 4 x schottky diode for bridge rectifier
• Smoothing cap (10 uF?)
• 2 x current sensing shunt (Igenerator, Ibattery) + 2 x TS1101
• IN system programming pins
• P - channel mosfet to switch off external power on fault (low battery / overcurrent)

• MCP1630
• LiIon app note

• Mounts with zip ties / verlcro straps on the frame between 2 tubes angeled at 120 deg
• 2 Shellswhich clip / screw together
• 5 mm wall thickness with a groove to place an O-ring between the shells
• AC input cable (2 pin)
• DC output + I2C cable (4 pin)

• Need mounting holes on PCB
• Case clamping the PCB doesn't work like that
• Case make teeth tighter
• Need to find less huge connectors for battery, dynamo and I2C
• Add OLED to case (Case and PCB can be made wider)

• connect pogo pin adapter to board and USB serial cable
• force flash voltage to 3.3V

$ espefuse.py set_flash_voltage 3.3V
espefuse.py v2.7
Connecting........_____....._
Enable internal flash voltage regulator (VDD_SDIO) to 3.3V.
The following efuses are burned: XPD_SDIO_FORCE, XPD_SDIO_REG, XPD_SDIO_TIEH.
This is an irreversible operation.
Type 'BURN' (all capitals) to continue.
BURN
VDD_SDIO setting complete.

$ esptool.py flash_id
esptool.py v2.7
Found 1 serial ports
Serial port /dev/ttyUSB0
Connecting........__
Detecting chip type... ESP32
Chip is ESP32D0WDQ5 (revision 1)
Features: WiFi, BT, Dual Core, 240MHz, VRef calibration in efuse, Coding Scheme None
Crystal is 40MHz
MAC: 40:f5:20:5c:8d:48
Uploading stub...
Running stub...
Stub running...
Manufacturer: c8
Device: 4018
Detected flash size: 16MB
Hard resetting via RTS pin..

• pio run -t uploadfs
• pio run -t upload -t monitor

You should see velogen booting up in the terminal.

• add 200k pulldown and 10 nF RC filter to speed sense pin
• add Zener diode across supply rail
• real buttons
• better connectors (waterproofing)
• Switchable battery power output for front light?
• Switchable 5 V output for WS2812