Audio Oscillator with Frequency Counter

  
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I am continuing to add DIY equipment to my home workshop. Audio oscillator is a very useful tool that is needed when we test audio projects. I already have a similar tool but it is just an oscillator without a frequency counter. I decided to use the schematic described in this page:. BTW, I have a deep respect for the owner of this site - there
Audio Oscillator with Frequency Counter - schematic

are tons of useful schematics, very well described and to this moment all projects which I have built from there work flawlessly. Anyway, back to my project. The original schematic has only sinusoidal output, but I wanted a square wave output also. This was achieved by utilizing forth opamp from TL084 IC and adding a couple of schmitt triggers to make a square wave signal. Audio frequencies are divided in three overlapping ranges: 18Hz - 230Hz, 180Hz - 2300Hz, 1800Hz - 23000Hz, which are switched with a rotary switch. Capacitors of Wien Bridge are soldered directly on that rotary switch. I made it with an enclosure from an old large capacitor. Inside are photoresistor and standard 5mm red LED. Outside is wrapped with a black tape to isolate from ambient light. The frequency counter was a challenge: there are many schematics on the web, but majority of them uses a microcontroller and I don`t have a PIC programmer yet. Finally I discovered a relatively simple circuit here:. Later I found almost the same circuit on this address:. The first has some errors, which I found too late and had to correct already etched PCB with some wires :) The schematic uses crystal to oscillate at 4. 194304 MHz and this frequency is then divided down to 1Hz, which is 1 second period. During this period input signal is counted and the result is displayed on six 7-segment LED indicators. The accuracy of the counter depends on the accuracy of the...



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