I've built the circuit shown in the snapshot below :
The parts list is:
- 2 - 1 Meg Resistors
- 1 - 2.2K Resistor
- 1 - 2N2222 transistor
- 1 - 47nF cap (Note: I actually used a 470nF cap in the one I built)
- 1 - ua741 op amp
- 1 - 3.5mm speaker output
I put the fritzing diagram together from watching the following youtube video: https://youtu.be/dAIQHkicIoo
Built Real Circuit
I have actually built that circuit on a bread board and tested it and it works great.
Question: How might I lower the frequency?
Now, I am interested in how I might change the frequency of the sound so that it might emit a lower tone.
2N2222 Generates Sound (amplified by op amp)
I am an electronics novice so I know very little about how this works but I am fairly sure the 2N2222 is generating the sound which is amplified by the op amp.
I also see the emitter seems to generate the input (signal) to pin 2 of the op amp via the 2.2K ohm 470nF cap part of the circuit. Is that the key to lowering the frequency that I hear?
If I increase resistance to that part of the circuit (lower input voltage to 741 input pin 2) would that cause the frequency to go lower? Would that mean I have to drive the circuit with more voltage since I'm adding resistance?
That's all just guesses.
Can someone tell me how I should alter the circuit to lower the frequency I hear?
Here's a very quick video I made so you can hear the sound? noise? that is created by the circuit.
YouTube Video Example : Using .1uF Cap In Place of 470pF I replaced the 470pF capacitor in my circuit with a .1uF cap (thanks to user to posted that answer) and now the noise is "lower" sounding to my ear. Whatever that means. :) See what you think.