The Double Touch device implements a double-sided, fMRI-safe touch input device. Electronic and/or ferromagnetic components are separated from the magnet by an extension cord (10+ meters of CAT-7 cable), allowing the Adapter Box to reside in the control room with the experimenter's computers and other non-MRI-safe equipment.
This project revolves around a Teensy 3.1 microcontroller, programmed in C++ using PlatformIO.
To build/upload the microcontroller code (OSX 10.11.1 "El Capitan"):
- Install PlatformIO
platformio runfrom inside theDoubleTouch/folder and answeryif it asks you to install the Teensy platform
WARNING! Although a normal CAT-7 ethernet cable is used to make the electrical connection between the touch panels and the Adapter box, it does not use the same signal levels as ethernet, and mixing the two could be destructive for all devices involved.
The Teensy manages two resistive-touch-screen controllers over its SPI bus.
Teensy and STMPE610 connections are:
| Teensy Pin Name | Teensy Function | STMPE610 Pin |
|---|---|---|
| 10 | CS (front) | SDA/CS (front panel only) |
| 11 | DOUT | SDI |
| 12 | DIN | SDO |
| 13 | SCK | SCL |
| 15 | CS (rear) | SDA/CS (rear panel only) |
| GND | Ground | GND |
| VIN | Vin | Vin |
| -- | -- | MODE connects to 3Vo |
X and Y pins for each touch panel connect to an RJ45 jack to allow the use of CAT-7 cable between the magnet room and the control room.
RJ45 Pinout (f stands for Front, r stands for Rear):
| RJ45 pin | Touch Overlay Side |
|---|---|
| 1 | fy- |
| 2 | fy+ |
| 3 | fx- |
| 4 | rx+ |
| 5 | rx- |
| 6 | fx+ |
| 7 | ry+ |
| 8 | ry- |
Note: opposing +/- connections form a twisted pair, intended to minimize noise and/or interference.
Modern operating systems usually provide drivers for both Serial-over-USB and Raw HID devices. However, OSX users may have to install FTDI drivers (and reboot) in order to use the Serial interface.
Both Serial-over-USB and Raw HID profiles are supported. Messages are sent from the Adapter to the PC every 10ms.
Message format is 6 values per line:
fx fy fz rx ry rz
Message format is a 64-byte array:
fx(MSB) fx(LSB) fz fy(MSB) fy(LSB) fz ... (remaining 58 bytes: all zeros)
Design Footnote The original concept of this was to implement a USB Mouse, but this idea was scrapped due to the fact that a USB Mouse can only have one pointer at a time. While it is possible to multiplex two "pointers" into a single mouse interface, I felt the extra complexity was not justified. The most appropriate interface for this device is, in my opinion, a multi-touch digitizer. This would expose functionality similar to that of a tablet computer, where two fingers can be used to zoom or scroll.
For now, a USB Digitizer is not supported because USB digitizer descriptors are not yet cross-platform, and implementing this device as a digitizer would tie users to a specific operating system. Some of the links under the
resources/folder may be helpful if someone wants to pursue that goal.