Friday, May 1, 2015

Digital Warrior - SD Card Mod

The parts for my very own Digital Warriors have arrived - and they really look good.
However, as pointed out in my last post, there were a few things I was missing among the functionality:

The Digital Warriors are based on the Teensy microcontroller development system, and consequently, the original design makes use of the Teensy's internal 2kb EEPROM to store its data. Naturally this tremendously limits the amount of data that can be saved.

To be able to use the Digital Warrior most flexibly and efficiently as a stand-alone sequencer, I wanted to use an SD card instead of the EEPROM. This would allow me to implement longer

Unfortunately all through-hole pins on the Teensy are already used by the Digital Warrior's standard functions. To make things worse, we can not freely choose any pins for the SD card access. SD cards are typically connected through the SPI ports and these are on: pin 13 - SCK, pin 11 - MOSI, pin 12 - MISO. Alternatively also pins 14, 7 and 8 can be used respectively, but these are also occupied. The fourth SPI pin, SS, is less of a problem as it is freely assignable.

Looking at the Digital Warrior firmware, it it quickly became clear that the necessary pins are easily re-routable. Pin 11 is used by one of the encoder push buttons, pin 12 the sequencer button, and pin 13 the track button. Changing the pin assignments in the software is pretty easy, rerouting them in hardware is also not really a problem. I decided to use the pads, on the bottom of the Teensy, 31, 32 and 33 for the button pin reroutings and soldered small cables on them before attaching the Teensy to the PCB:



Then I removed the corresponding pins from the headers which I used to solder the Teensy to the pcb. And finally connected the cables to the corresponding spots on the board:





A quick test with my updated firmware confirmed that everything was working well.


Similarly, for the SD card, I decided to use pad 29 for the SS pin, and added a small cable here as well:



Afterwards I soldered the Teensy to the PCB and connect the remaining cables (the purple one was too much) to pins 11 (brown), 12 (red), 13 (grey) as well as GND (black) and 3.3V (white). The other side got soldered to the corresponding points on the micro SD adapter  as described here, and voilĂ  - done:


The first version of the Ghz Warrior firmware to start using the SD card instead of the EEPROM can be found on my GitHub page.

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