simple theremin circuit

Discussion in 'The Projects Forum' started by ball, May 10, 2011.

  1. ball

    Thread Starter New Member

    May 9, 2011
    7
    0
    I am building a simple theremin to demo for my physics class, and I found this schematic online that was the least complicated I could find. I built it on a pcb to minimize the capacitance of the connections, but when I connected the output ("Ausgang") to the tip of a headphone jack (to an amplifier) and the ground to the sleeve, all I get is static. I apologize for my complete lack of understanding of this circuit but I don't know where to start troubleshooting it. the "4093" logic gates are NAND gates, and the "4077" gate is a XNOR gate. I used 3 Quad two input NOR gates wired to work like 2 NANDs and a XNOR gate. for the antenna I used a 6 inch long by 3/4" OD steel pipe. The static does seem to change volume with the distance my hand is away from the pipe. I would GREATLY appreciate any help with this circuit.
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,669
    804
    That could be the problem, maybe the delay through the nor gates is too great to get the oscillator running. What does the circuit do when you change the 20K resistor?
    Do you have an oscilloscope to see what is actually happening? If not, try to get the original parts and see what it does.
    Also, do you have the circuit on a breadboard, or how are the parts connected? The most reliable would be bending the pins of the IC and soldering the parts with short leads straight to it.
     
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