A collection of circuits of mine done in past that were captured on computer in process of making PCB. Just found these one day when trying to do bit of PC housekeeping.

If any one interested in, you can mail me circuits{{{AT}}}}far-out.demon.co.uk.

THis syncrhonises 2 floppy disk drives together so that data may be copied from one disk to other. Copies protected disks very easily as it does by blindly transferring the data edges without processing any of it. One FDD motor's speed control clock is derived from the VCO's output so as disk rpm can be controlled. The circuit continually trims this FDD motor speed, when both FDD's are in sync a whole track is transferred in one go, copy protection data included. Every other Index pulse switches between Write and not Write, and every other Write switches between Head 0 & Head 1, every other this steps the head one more track. When the stepping sound changes the disk is 'Done'

A diode photodetector on each input detects chopped light, ie a infrared LED. In the path to one of the detectors is a variable, such as light reflected from surface of water or say a sample of which the light transmission is to be measured. Chopped light because so the whole thing can works in broad daylight. Tha't why this circuit seems is complicated

4 sample and holds, one for each detector output level when light is on and off. The dark level subtracted from the light level, then the difference between these is detected and output.

Technical description of the Oil Detector circuit.

The IR receiving photo diodes are used in the short-circuit mode. Each op-amp's output voltage being proportional to it's photo detector current * the feedback resistance.
At zero photo-current, the output voltage is the same as the non-inverting inputs which are in turn clamped to the Vstab level of around 3V. This 'jacked-up' level is to ensure that the IC outputs do not try to swing below 0V and cause erratic operation, as split supplies are not used in this design for the sake of simplicity.

IC3 is configured as two subtractive amplifiers having a gain of 2. The output of each amplifier is a product of the difference of the inputs *2.

The 555 oscillator runs continously and gates the LED on and off. The duty cycle is about 50%.

While the LED is on, the output of the photo amplifiers charge the upper capacitors of the subtractors (C4, C6) via the analogue switch 4066. When the LED is off, the lower capacitors are charged (C5, C7).

The resultant output is that which is due to the in-phase voltage shift of the photo-amplifiers output while the LED is on only. Any ambient light, steady or fluctuating is cancelled out.

The reference detector is used to monitor the output of the LED. A servo loop is used to maintain the LED light output constant. The LED current is automatically adjusted by IC4 so that the feed back signal on R14 matches that of the Vref level presented to it's non inverting (servo set-point) input. The value of the reference photo- amplifier's feedback resistor sets the LED power. The optical coupling betweem these devices will affect this level.

IC4's output is capable of driving the LED directly. R15 is included to prevent overcurrent if servo coupling is lost.

C4: Ref LED on level
C5: Ref LED off level
C6: Sig LED on level
C7: Sig LED off level


sensitive version amplifiys the signal twice.

This is a latching version, interrrupt suplpy to reset.

pcb done by cad

Check Plot

Top Screen print used componenet placement guide

Download the artwork: for the above circuit board.

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