Metronome beep to switch on/off...?

Discussion in 'The Projects Forum' started by prometei, Jul 21, 2012.

  1. prometei

    Thread Starter Well-Known Member

    Apr 13, 2008

    I haven't done anything with electronics for a few years, forgotten most of the stuff I've learned, so I'm having trouble now figuring something out:

    I have a simple metronome that beeps the BPM (Tempo beats per minute). Here is a screen-shot of how 96 BPM looks on the scope:


    So the beeps are short sine/square waves about 2.2 Voltage, positive and negative.

    I want to build a circuit that will close a switch on/off (of another circuit) according to the tempo beeped by the metronome.

    Can you guys recommend a simple schematic, either with a relay or with transistor, or maybe it could be done by using a opto-coupler?

    thanks in advance
  2. DickCappels


    Aug 21, 2008
    Yes...amplify the pulses and apply them through a large resistor (so that the input protection diodes can clamp the excess voltage safely) to the input of a CMOS D Flip-Flop. Connect the "Not Q" output to D. Tie the set and reset inputs to VSS or VDD, depending up which flip-flop you use so that they are not active.

    Connect VDD to the metronome's power supply if the voltage is within flip-flop's allowable power supply voltage range. Connect VSS to ground.

    The amplifier:
    Take the input through a 1k resistor to the base a small signal NPN transistor such as the 2N2222. Ground the emitter. Run a 10k resistor from from the collector of the transistor to the positive power supply for the flip-flop. Also connect the collector the clock input of the flip-flop.

    You will get your switching signal on the Q and "Not Q" outputs.