How to Make your Device Compatible with Tecla
The specifications below will be useful to those porting the Tecla App to platforms other than Android as well as those interested in supporting switch access through the Tecla Shield on embedded devices such as automated teller, checkout and ticket vending machines.
Summary
- The Tecla Shield acts as Bluetooth server hosting an Serial Port Profile connection.
- Physical switch connections are normally open (HIGH), closing to common (LOW).
- Switch events are broadcast through a virtual serial port at a 115200 baud rate.
Switch Event Anatomy
Once a device establishes a SPP/RFCOMM connection with the Tecla Shield, it will receive a byte on every switch state change. This byte will contain the state of all switches connected to the Tecla Shield, according to the following table:
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|---|---|---|---|---|---|---|---|---|
| Name | - | - | E2 | E1 | J4 | J3 | J2 | J1 |
| Initial Value | LOW | LOW | HIGH | HIGH | HIGH | HIGH | HIGH | HIGH |
| Port | - | - | Switch 1 | Switch 2 | ECU | ECU | ECU | ECU |
| Pin | - | - | - | - | 4 | 3 | 2 | 1 |
Bits 0..3 – J1..4
Up to four (4) generic switch inputs connected to DE9 male header on Tecla Shield. Follows the standard configuration of wheelchair ECUs. Typically assigned to directional (i.e., forwad, backward, right & left) actions in wheelchair joysticks or adapted switches.
Bits 4..5 – E1..2
Up to two (2) generic switch inputs connected to 3.5mm mono sockets on the Tecla Shield. Follows the standard configuration of ability switches.
Echoing function
The Tecla Shield includes an echoing function that allows for connections to be monitored from a client device. Any character sent to the Tecla Shield will be immediately echoed as long as there is a stable connection. A byte that cannot be confused with switch events (e.g., 0×70) should be used for this function.
