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G6Tanuki · 21st Mar 2019, 9:18 am

A possible 'old-style' circuit-source idea: in the 70s and 80s there were various projects in Practical Electronics, Elektor etc. for car rev-counters.

Some were very simple - a 'debounce' circuit [Schmitt-trigger or 555] to square-up the wobbly waveform from the contact-breaker-points followed by a diode/capacitor "charge-pump" as frequency-to-voltage converter, then an emitter-follower to drive the meter.

Others were more-sophisticated - using a PLL. I even recall one that did it all digitally and drove a 3-digit 7-segment display, using CMOS logic.

I guess these days an Arduino and cheap LCD display would be the way to go.

21st Mar 2019, 9:18 am	#2
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: Low frequency indicator? A possible 'old-style' circuit-source idea: in the 70s and 80s there were various projects in Practical Electronics, Elektor etc. for car rev-counters. Some were very simple - a 'debounce' circuit [Schmitt-trigger or 555] to square-up the wobbly waveform from the contact-breaker-points followed by a diode/capacitor "charge-pump" as frequency-to-voltage converter, then an emitter-follower to drive the meter. Others were more-sophisticated - using a PLL. I even recall one that did it all digitally and drove a 3-digit 7-segment display, using CMOS logic. I guess these days an Arduino and cheap LCD display would be the way to go.