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+# OpenPrepPad
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+
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+This allows use of the Orange Chef Prep Pad on Linux (and maybe OSX) machines.
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+
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+Make sure bluetooth is powered on when running. You can run it by
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+
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+```
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+npm install
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+npm start
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+```
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+
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+## Protocol Details
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+
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+The Prep Pad is a standard Bluetooth LE device and exposes all functionality via
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+GATT. The relevant service is `ffa0` which is the Accelerometer service. You
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+then need to write `0x01` to characteristic `ffa1` which is "Accel Enable".
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+After this, you should be able to listen to characteristic `ffa3` which is
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+"Accel X-Coordinate". This should give you a stream of little endian 32-bit
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+integers. Heavier is less while lighter is greater. To convert the value to
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+grams, you can divide the value by 14 and that should be it. Writing `0x00` to
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+"Accel Enable" will cause the device to disconnect and turn off.
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+
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+The other available characteristics are `ffa2` which is "Accel Range". It's
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+read/write but I don't know what the values are supposed to mean. `ffa4` and
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+`ffa5` are "Accel Y-Coordinate" and "Accel Z-Coordinate" but I didn't find those
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+values changing often.
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+
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+There is another service `f000ffc0-0451-4000-b000-000000000000` which contains
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+characteristics `f000ffc1-...` and `f000ffc2-...` for "Img Block" and "Img
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+Identify", but I don't know what those are.
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+
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+## Light Indicator
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+
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+When it's off and you press the button, the light constantly flashes which means
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+it's waiting for a connection. Once something connects, the light will remain
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+steady. After writing `0x01` to "Accel Range", the light will turn off but the
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+device is still on and sending data. If you disconnect during this, the device
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+will remain on but the light will remain off. Even when you reconnect, the light
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+will not turn on again but that's normal.
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+
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+When it's on, and you press the button, the light will flash twice for a longer
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+interval than when it's waiting for connections. After that, it will turn off.
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+
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+## Device Quirks
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+
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+Normally the device continuously sends data but I've found that it will
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+sometimes enter a weird state where it will send 8-10 values and then
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+disconnect. Even after reconnecting, it will still just send 8-10 values and
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+disconnect. Restarting the device seems to fix the problem.
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+
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+Another issue I've found is that the data received from the device is delayed.
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+I'm not sure if this is a problem with bluetooth or if the device itself is
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+sending it with lag.
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+
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+I have experienced some occasions where the device itself hangs. Pressing the
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+button doesn't do anything, the light doesn't respond. I had to physically
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+remove the batteries to get it responding again. I'm not sure if this is just
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+because I'm not connecting/disconnecting properly.
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+
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+This might be obvious but the device's 4 stubby legs must be on a firm surface
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+for it to work correctly since those are the things that are actually connected
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+to the sensor. The entire top body is just one solid piece and the legs are the
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+things that actually "move".
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+
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+## Reference
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+
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+I found this [book preview][1] pretty handy for understanding Bluetooth LE /
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+GATT. Besides that, playing with bluetoothctl is pretty handy for exploring
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+what's on the device itself.
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+
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+[1]: https://www.safaribooksonline.com/library/view/getting-started-with/9781491900550/ch04.html
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