This is Raspberry Pi GPIO connector breakout board with some additional features:
- “Real” or “passive” PoE with 12V output
- 5V DC/DC module
- Additional 3,3V regulator
- ESD protection on all GPIO pins
- two additional pins for each pin on R.Pi 40 pin GPIO connector
- Separate UART and I2C headers
- 3,3V Supply for periphery is selectable: from R.Pi or from external regulator
- STM32F070 or similar in TSSOP-20 housing for controlling additional sensor or any other hardware
- Jumper for Cortex-M0 / R.Pi UART connection
This is revision 1.0 – work in progress and the PCB boards are not yet produced (the order is out). For now I will briefly explain the schematics.
The power supply is based on Silvertel Ag9700 PoE module. It is IEEE 802.3af compliant module with 12, 5 or 3V isolated output (1500V barrier) delivering 12W of power when proper PoE injector is used. Input voltage has wide operating range. I bought samples via distribution and the price was about 8 EUR per module.
If this price is too high, there is “Ghetto” option for “passive” PoE. It simply connects unused twisted pairs to the input of the 5V DC/DC. Unfortunately with such solution there is no galvanic isolation. Two 0 ohm jumpers are provided for this: R3 and R4. They can be replaced with fuses as well.
Few words about ethernet connection:
The cable from the outside is connected directly to the heaqder without the RJ45 cable connector. I did this way for simpler installation in the IP65 plastic or metal housings. I put one RJ45 female plug to connect the R.Pi ethernet through short (5-10cm) patch cable.
Next section is microcontroller. It has SWD debug header and all pins connected to 100 mils headers. The UART PA2/PA3 can be connected to R.Pi UART GPIO14/GPIO15 via two 0 ohm jumpers R1 and R2:
And finally, there are headers for I2C0, I2C1, 1 wire, UART0 and selecting header for 3,3V supply:
The PCB is 56x68mm and slightly covers the display connector of the R.Pi. Other connectors are free.
There are additional pads with +3,3V, +5V and +12V as well. Please check the complete schematic for further details.
Stay tuned for further details about progress (when PCBs arrive).