Tuesday, November 8, 2011

The connections

In the end, I controlled three aspects of the slide projector from the Arduino board:

  1. Moving forward / back slides
  2. Turning the lamp on and off
  3. Rotating the lazy Susan
To move the slides forward / back, I replaced the wired remote control connector with connections to relays (it was a standard 6 pin DIN connector) - I left it on for 0.5 sec, then waited 1.5 seconds before pressing it again.

To turn the lamp on and off, there is a special connector on the side. I have never seen something like it, and couldn't find a replacement plug. So I drilled a hole in the side to pull out the two wires that were soldered together inside. Apparently when people did presentations with multiple slide projectors, this connector was used to fade between projectors, etc. Ah, those were the days. I then connected these two wires to a relay. The first one started to smoke - I got a more powerful one (240V, 3A), but after using it for a few minutes it started to smell also so I took it out. I guess the current that is passing through the globe is passing through this connection, so maybe I need one with a higher current rating.

The last two connections out were connected to the motor controller (see previous post). If one is high and the other low, the motor will rotate clockwise, and vice versa for anticlockwise. If I set both to low, then the motor does not move.

For these last three connectors, I used the servo connectors on the demo board, and modified the arduino code to just send digital on or off (as opposed to PWM (pulse-width modulation) which is required for the servos).

The motor

I wanted the motor to be able to rotate the slide projector (which was sitting on a lazy Susan from Ikea) either clockwise or counter-clockwise. The advice I constantly got was to use an H-bridge, however, no-one could tell me where to get one. There were numerous Arduino shields available, but the form factor of the Android demo-kit (it has more pins than the standard ones) meant that it wouldn't fit. Eventually I found a place in Australia (in Perth) that had something appropriate, and I ended up using this one which arrived in two days.
It was tiny! Eventually I managed to solder on the legs and understand how to get it working. 

Unfortunately, I eventually turned off the motor feature for the demo at the GDD. I had planned to use the compass as feedback in order to turn the slide projector to face in the direction where the rainbow would be seen (directly opposite the sun). However, I think the magnetic field caused by the slide projector (probably a transformer) caused the compass to be inaccurate. I guess I will need to use another feedback method to know what the orientation of the lazy Susan is (suggestions welcome).

Google Developer Day

Google developer day has arrived (quickly!) There are a lot of people here!

Most of the desired features were implemented, the only main problem was setting the orientation - I could not get an accurate orientation from the compass, so I disabled this feature. I'm not sure if the slide projector was generating a magnetic field and interfering, or because the tablet was not exactly horizontal.

I'm demonstrating the device in the "Google cafe" area during the breaks. In the last session, I'll also be presenting a talk on "How to see a rainbow" in the Ignite session (5 minute talks).

I'll add the rest of the details of the implementation shortly.