Modelers in different disciplines often have to deal with the problem of determining the speed of rotation of the parts, screws, shafts, and even cassette recorders. That’s what the device advises to use well-known Polish engineer, Janusz Wojciechowski.
Rotating propeller of the model plane with a certain frequency covers the light sensor (phototransistor) and an alternating current. Alternating current is amplified by low frequency amplifier transistors T2, T3, T4, is rectified by diodes D1 and D2 and a DC current is fixed by a galvanometer (or microammeter) sensitivity 100-500 µa (of any type).
Sensor — T1 — a common type transistor МП39—МП42 with sawn through the window or outdoor. The transistors T2, T3, T4 — MP35—MP38.
The value of the resistor R12 is selected depending on the supply voltage, so that the stabilizer type was Д815И voltage 4.7 V (for Д815А — 5.6 in). Estimated value of the values of the resistor R12 on the circuit diagram.
The instrument can measure rpm via reflected beam. On the rotating parts need to make a label with white paint or glue (rubber glue) a strip of thin foil.
Calibration of the instrument (dial indicator) is exactly the same as in the first embodiment.
The resistance of the R12 resistor—220 ω (12 V) 120 Ohm (9 in), 47 Ohm (6 in) is selected for normalization. Resistor R11 regulator zero microammeter Diodes D1—D2—Д2Е, D9.
Schematic of the device with fotodechicas
A — for dust protection outdoor the resistor is closed at the top by a thin plate of Plexiglas, or celluloid (glued emalita or supercement), B — determining the number of revolutions reflected beam, In the gap, G — circuit rectifier on the basis of the filament transformer (6.3 V) to supply illuminating light bulbs from AC DC. W is Roy variant power from the battery or from the battery.