Saw-tooth oscillator

[Blunderland]

http://www.electronic-circuits-diagrams ... ages/2.gif

I keep trying to build this schematic. I put an LED on the output to check whether it's working it lights up but then when I output to a speaker I get no saw tooth wave.

Are both resistors 2.2k? And what uF should the capacitor be? Also if I wanted to use a pot to change the pitch which resistor would I replace?

[pebe]

Your problem is that the circuit does not provide enough power to drive a loudspeaker. You need to connect it to the input of an amplifier like an LM386, and connect your loudspeaker to the output.

The frequency (pitch) of the output depends on R and C. The BC557 in your circuit is configured as a constant current source that charges C, so frequency will also depend on the supply voltage. With a 2.7V zener the voltage across R will always be 2V when the transistor is conducting, so if you make R = 1K then it will pass 2/1000 = 2mA. If you make supply = 9V then C will have to charge 3V each time.

Assuming the discharge time is short and can be ignored, then the frequency can be calculated from
F= I/(C x V) = 2mA/(1millionth x 3) = 500Hz. Increasing R or C will reduce the frequency and vice versa. Don't reduce R below 100ohms.

I hope that helps.