DIY Turbojet Engine Control RPM circuit

anaxcontrol

Hello fellow members,

Still plugging away at making a 300ft/lb small scale jet engine. Was wondering if anyone can enlighten me on the best way to get RPMs from a spinning shaft (up to 125K RPM) using Infrared LEDs. I have some sample code but looks like it might be limited. I'm going to paint half of a large nut gloss white and half flat black to produce the variation. I should see a 1v to 3.3v fluctuation as the shaft turns. What is the best way to get this coded? using the built in Schmitt trigger (Stamp PX2)? the attached is the circuit.

kwinn

I would suggest using a 555 timer after Q1. That provides you with two comparators, better sensitivity, and a clean output waveform for the BS2. You can use the "count" instruction to count the pulses for a specific time to measure the frequency.

anaxcontrol

Thanks kwinn. Anyone have some code I can use for this purpose?

kwinn

For a count duration of one second the code would be:

COUNT Pin, Duration, Pulses
RPM = Pulses x 60

Duration would depend on the Basic Stamp being used. For a BS2px the basic count period is 287uSec so it would be 1,000,000,/ 287 = 3,484 (actually 3,484.3205574........etc) so the reading would be low by approximately 0.001%.