Open source client for Orange Chef Prep Pad
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README.md

OpenPrepPad

This allows use of the Orange Chef Prep Pad on Linux (and maybe OSX) machines.

Make sure bluetooth is powered on when running. You can run it by

npm install
npm start

Protocol Details

The Prep Pad is a standard Bluetooth LE device and exposes all functionality via GATT. The relevant service is ffa0 which is the Accelerometer service. You then need to write 0x01 to characteristic ffa1 which is "Accel Enable". After this, you should be able to listen to characteristic ffa3 which is "Accel X-Coordinate". This should give you a stream of little endian 32-bit integers. Heavier is less while lighter is greater. To convert the value to grams, you can divide the value by 14 and that should be it. Writing 0x00 to "Accel Enable" will cause the device to disconnect and turn off.

The other available characteristics are ffa2 which is "Accel Range". It's read/write but I don't know what the values are supposed to mean. ffa4 and ffa5 are "Accel Y-Coordinate" and "Accel Z-Coordinate" but I didn't find those values changing often.

There is another service f000ffc0-0451-4000-b000-000000000000 which contains characteristics f000ffc1-... and f000ffc2-... for "Img Block" and "Img Identify", but I don't know what those are.

Light Indicator

When it's off and you press the button, the light constantly flashes which means it's waiting for a connection. Once something connects, the light will remain steady. After writing 0x01 to "Accel Range", the light will turn off but the device is still on and sending data. If you disconnect during this, the device will remain on but the light will remain off. Even when you reconnect, the light will not turn on again but that's normal.

When it's on, and you press the button, the light will flash twice for a longer interval than when it's waiting for connections. After that, it will turn off.

Device Quirks

Normally the device continuously sends data but I've found that it will sometimes enter a weird state where it will send 8-10 values and then disconnect. Even after reconnecting, it will still just send 8-10 values and disconnect. Restarting the device seems to fix the problem.

Another issue I've found is that the data received from the device is delayed. I'm not sure if this is a problem with bluetooth or if the device itself is sending it with lag.

I have experienced some occasions where the device itself hangs. Pressing the button doesn't do anything, the light doesn't respond. I had to physically remove the batteries to get it responding again. I'm not sure if this is just because I'm not connecting/disconnecting properly.

This might be obvious but the device's 4 stubby legs must be on a firm surface for it to work correctly since those are the things that are actually connected to the sensor. The entire top body is just one solid piece and the legs are the things that actually "move".

Reference

I found this book preview pretty handy for understanding Bluetooth LE / GATT. Besides that, playing with bluetoothctl is pretty handy for exploring what's on the device itself.