Sunday, February 1, 2015

Short Circuit - Part 1

I've  got my hands on the Zumo 1.2 robot and it's time to do some crazy stuff with it. Last month i finished designing a customized baseboard for the Teensy 3.1 Cortex-M4 board by PJRC. This baseboard was tailored specifically for the Zumo. More details on the Zumo 1.2 can be found here. The zumo is designed such that it acts as a shield for the arduino uno board. However if you mount the standard original arduino on the zumo, you cannot mount other shelds. Some pins are specific to the Zumo which you can check on the Zumo wiki. Some of my friends who are founders of Entesla managed to give me one of their arduino clones - the Entuino with all the headers removed. I soldered the new headers as per my convienience, removed the DC jack and reset switch and it looks like this.

When mounted on the Zumo the board looks like this. Now i can mount an infinite number shields on top of this board (conditions apply....even mathematically :P)

Notice that few of the pins have been cut off such that they do not interfere with the shield on top. These are primarily the controls for the zumo motors that were mapped to the same pins used by SPI. The power pins too were not made available to shields above the entuino. The Teensy board has its own voltage regulators for 5V and 3.3 V and hence sources from the Vin supply from the Zumo shield which is 7.5 V

I will be using the arduino for the sole purpose of controlling the motors. All the sensors' data computation will be taken care by the Teensy over the I2C bus. The teensy and entuino communicate with each other via the hardware UARTs, (0, 1) on the entuino and (0,1) Serial1 on the Teensy. The Teensy also has a NRF24L01+ interfaced over the SPI bus for remotely controlling the bot and for data telemetry. The Teensy base board also has support for the ESP8266 wifi (not connected) and a 40 pin header to connect the Raspberry Pi. The Teesny baseboard and the RPi communicate over the UART. The whole block diagram of the entire system is shown below. Currently the ESP8266 and RPi are not connected to the teensy baseboard. Initially i had planned to use the SoftwareSerial library on the teensy for comms between teensy and entuino, but that backfired as the SoftSerial library is defunct. Therefore, i patched the ESP uart to the hardware uart of the entuino (the white wires in pics below).

The fully assembled robot.

The two boards

Now i have to take utmost care to solder the 40 pin header whose component side is behind the board. R.I.P ESP8266. #facepalm, softwareserial #fail.

The Eagle schematic. Not perfect i must say, jeez, look at some vias and those clearances... :P

Fully Powered Up

More adventures with this in Short Circuit - Part 2.

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