Alarm triggered via accelerometer (Tessel 1) causes a photo to be taken (Tessel 2). Alarm + photo are displayed in a HTML5 client, which also allows arming, disarming and canceling the alarm.
Note:
- Taking the picture on the Tessel takes about 2.4s at a very low resolution.
- Encoding this for sending over WAMP is another ~1.3s.
- The Tessel's wi-fi is also slow.
- So don't expect a snappy response with the image.
Two Tessels, one with an accelerometer module, one with a camera module.
The demo backend runs on Node.js, and the Tessel uses the node package manager npm - so you need to have both installed.
To install the required Node packages, you initially need to do
npm install
in the demo directory.
Then start Crossbar.io from the demo directory by doing
crossbar start
Crossbar also serves the HTML5 frontend under http://localhost:8080.
For the two Tessel scripts, you need to replace the IP in url: "ws://192.168.1.134:8080/ws" with the IP under which the Tessels can reach the computer running Crossbar.io.
Connect the Tessel with the accelerometer and do
tessel push tessel/accelerometer.js
the disconnect and restart.
For the Tessel with the camera do
tessel push tessel/camera.js
Since the Tessel WS/WAMP libraries do not send the proper WebSocket subprotocol parameters, in the Crossbar configuration ignoring this needs to be set:
"type": "websocket",
"options": {
"require_websocket_subprotocol": false
}
Since the Tessel has problems with WebSocket pings, do not set auto_ping_interval to anything but the default 0.
As a consequence of not having the pings, Crossbar.io will most likely not detect the loss of connection when redeploying code on the Tessel. It is easiest to handle this by restarting Crossbar.io before each code redeployment.
When called from the frontend, the remote procedure for taking pictures on the Tessel provides progressive results. This is an easy method to allow feedback about long-running operations.