In building a simple guitar tuner I had hoped to demonstrate that one could interchange the positive time interval resistor R1, and the negative time interval resistor R2 to control the charging and discharging of the .01uf capacitor to generate a desired tone on the speaker. This should still be possible, but first I need to find the disconnection between theory and reality.
In engineering we want to control as many factors as possible so that we can isolate the unknown factors and test them in a strictly controlled environment. In the meantime, however, I have chosen a quick fix solution and will return to the problem in a later blog post.
Yesterday, my wife wanted Chinese food. It takes about ten minutes to prepare the food for take-out and this was just enough time for me to run over to Radio Shack. While I was there I bought a 100K micro-size potentiometer.
The temporary fix for the 555 guitar tuner incorrect frequency problem is to remove the “R2” resistors (100K, 10K, and 3.3K) from the previous circuit:
Then replace them with my new 100K micro-size potentiometer and a 68K resistor
The R1 resistor is 100K. With the 68K resistor on R2, the circuit will need somewhere between 113K and 114K on the 100 K potentiometer. Set the potentiometer to about half a turn with a small screw driver. I used my electronic keyboard and selected the square wave tone, then switched on my 555 timer tuner.
I held the A4 key down on the keyboard and used the screwdriver to turn the potentiometer until the frequencies matched.
Yep. It’s a kludge, but it will do for now to demonstrate how to build a “555 Guituner,” or guitar tuner built using a 555 timer IC.