Sunbird

Version: rev11.

Technical information

This is a board designed around an off-the-shelf ESP8266 ESP-12(E|F|S) module.

Component choices

• ESP8266 single-core 160Mhz 32 bit microcontroller with Wifi, 32K RAM and 4MB ROM as main CPU.
• 2x 5050 RGB notification LEDs on either side of the PCB at the rear end
• USB C charge and programming port.
• CH340g USB UART controller, with automatic reset circuitry for programming CPU.
• FS312F-G (and associated double-mosfet) short circuit protection circuitry. This also provides overcharge/overdischarge protection
• TP4056 li-ion battery charger circuit. CHRG and STDBY signals passed through to CPU.
• ADXL345 Accellerometer for smart-power-off and usage detection using i2c bus with interrupt line.
• FM116B motor driver H-bridge IC. Warning: Datasheet almost entirely in Chinese.
• Integrated 500mA fuse on PCB.
• Standardised around 0603 size components where possible.
• Tag-Connect TC2030 no-legs zero-pcb-parts connector used for programming and debugging before the CH340G is brought up, and for diagnosis when the CH340G is not populated, or otherwise unavailable due to failure.

Technical features

• Ability to field-program in-situ using USB bus.
• Ability to OTA (Over The Air) program device.
• Ability to sample battery voltage without incurring passive current draw, using 2 high-resistence resistors and a single transitor to enable battery sampling.
• Ability to run while charging battery.
• Ability to show status using RGB colour LED on both sides of circuit board.

Known issues

• 3.3v regulator has been problematic so far. Hopefully resolved in rev11.
• 5050 RGB LEDs don't have consistent pinout of which colour channel is on which pin, meaning the value of R8020-22 are unpredictable, and subject to change before assembly. I have debated using WS2812B or similar as a replacement, but increasing parts cost and program complexity deterred me.

Licencing

Sunbird is licenced under the Open Hardware TAPR licence.

PCB

Schematics

Processor

Battery Charger Circuit

Power Regulator

Motor Driver

USB UART