The thing to do now was get the synchronising working. The detector has no markings, only two leads, and is polorised (positive is marked on the board). I couldnt find a similar image on google, but has to be a photodiode or phototransister, not knowing which means I didnt have a circuit to try. I connected it up to the multimeter to see what it does, it give high resistance by default then low resistance when lit. I decided to connect it to a MCU pin and ground and see if that worked, at low speed it did intermittedly and at high speed it didnt.

The best way to use this would be to get it to produce an interrupt which would start the image drawing, so I set up the micro to detect a pin change, this didnt work at all. Did I have the interrupt set up correctly, was the Leostick exactly the same as a Leonardo, were interrupts the same? Having everything set on a spinning board was making it difficult to test things out, I had no debugging, the motor would run as soon as I turned on the power, I needed to power the device because it drove the timing ir led. There was a momentery kill switch for the motor as part of the original device so I could use this to test the led trigger but still it was frustrating.

I was hoping to get this running without adding circuitry but now I was thinking transisters as a switch for the interrupt. I gave it a go and it didnt work, maybe I needed a second transister so one was an amplifier and the second was a switch, this didnt work. Now I was thinking Ill have to set up biasing using resisters, I gave it a go but it didnt work.

Now I started thinking about the original board, this had some transistors, capacitors and resistors, maybe they were all part of the triggering circuit. I got the multi meter out and followed the traces which were hard to see because everything was painted black, after poking around for awhile I wasnt getting anywhere, the detector did connect up to this circuit but visualising it was difficult. I though if I scrap away the paint I could see where everything goes and draw the circuit, so that I did. The circuit had a lot of filtering but essentually the detector connected to one transister which connected to another and there were a few lines which went to the controller. At this stage I thought this circuit is designed to do what I need done, its already miniturised I could cut it off and use it. I did that and it didnt work.

My last attempt was to use a voltage comparitor, which doidnt work.

The problem seemed to be that the interrupt pin was providing a +5v and stuffing up every circuit Ide build, but the detector needed power to work and my electronics theory wasnt good enough to work out what to do. As a last resort I thought I could use a Halls effect device and a magnet, atleast I would know what Im dealing with, but the led and detecor should work (it did originally).

Eventually I thought what if I just use an analog pin, the detector worked with the multimeter. I set up a test using a variable resistor between the +5v and an analog pin which had the positive end of the detector connected, and the negative end of the detector to ground. I wrote a program to turn on the pin 13 led if a pulse was detected then varied the resistor while moving the detector over the led, it worked. I subsituted a fixed resistor for the variable one, soldered everything to the Leostick and it all worked. This method isnt acurate, the image wil flick back and forth a bit, but it works and Im relieved