## A2 ELEC6 CW Update

##### Nov 26, 16 - 01:12am, 1 year and 5 months ago

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 $V_-$ and $V_+$ via:

Where A = the open loop gain of $10^6$ volts (of course this is limited by the supply). So if for example the voltage at the non-inverting input ($V_+$) 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 $V_{out}$ 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.

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