It has been a while since I’ve made any visible progress on the LED cube, but the first revision of the TOH (Teensy+OctoWS2811+RPi Hat) PCB arrived from China towards the end of July.
Features of TeensyOctoHat v1.0
- Teensy 3.1
- OctoWS2811 Adaptor
- Onboard battery and RTC crystal
- SD Card socket (SPI)
- 16MB flash memory (SPI)
- Raspberry Pi HAT EEPROM (I2C)
- Battery input with UPS style features (GPIO4)
- Power and user controlled LED (D10)
- Powered via RPi or back powering the RPI via USB or battery
- 4 PWM outputs for FAN control (D22/D23/D25/D32)
- Input for one wire temperature sensor (DS18B20) chain (D17)
- Serial connection to RPi (D0/D1).
After assembling the board I noticed there was a few problems with the design (as expected). The first thing I noticed was the solder mask was missing on the lower left part of the board as the trace was too close to the mounting hole. Then came other issues such as using an analogue only input as the chip select on both the EEPROM and SD card so the PWM fan controls was re-purposed to allow testing. I also added a pull-up resistor between the battery power switch (UPS) and the RPi. The pull-up connected to the 5V UPS supply via a 100k resistor which should be safe as it only leaks ~17uA into the 3.3v max RPi GPIO.
Version 1.1 of the board has a few modifications and more features. I’d been concerned about the MK20DX256VLH7 3.3v output being capable of supplying enough power for the SD card, under testing it all looked OK but seeing the release of Teensy 3.2 I decided to follow their lead and add a 3.3v regulator.
Additional features of TeensyOctoHat v1.1
- Pads for a temperature sensor (DS18B20Z) on the bottom of the board (between the TOH and RPi) and pull-up resistor.
- An alternate method of powering TOH (and the RPi with back powering protection) on a set of pin headers.
- Ability to measure the input voltages on the USB, Battery UPS and alt power inputs.
- More I/O pins (D9/D29/D30/D33) broken out.
- Dedicated 3.3v LDO regulator.
- Smaller crystal
The gerbers have been sent for manufacture so version 1.1 should be ready for testing in a couple of weeks.