So this is what I’ve built so far in a week or so:
Basically I’ve set up the photo-transistors in a sort of array, with a 331N comparator to convert the analogue signal from the photo-transistor into a digital one, the output from the 311N then goes into some LED’s so I can debug it easier later down the line.
The 311N works the same way as a 741, except it doesn’t loose voltage gain at high frequency inputs, I use a set voltage level, for the non-inverting input to 0V, and the voltage to the inverting input to the photo-transistor. The photo-transistor has a feedback loop resistor of 10MOhms to provide a lot of voltage gain, since 1 photon hitting the sensor = 1 electron, which is suuuuper low.
The 311N compares both and via:
Where A = the open loop gain of volts (of course this is limited by the supply). So if for example the voltage at the non-inverting input () is greater than the voltage at the inverting input, even by 10 microvolts, since the open loop gain is so large, any difference is massively amplified, thus giving a high at because:
I’ve also set up a simple electromagnetic relay switch, which can provide 12V, up to 10A, the stepper motor I’m using requires 3A, so it’s more than suffice.
And finally I’ve started work on a MOSFET H-bridge, which is controlled by the 28X1 PICAXE micro-controller, to control the stepper’s step speed, i.e. length of music note in my project. There’s also a simple voltage follower to limit the input voltage to the micro-controller to 5V, so not to damage it.