I need decent adjustability with my pot, can I achieve this?

A 10k pot doesn't give you a 100:1 turn-up ratio (0.25 to 25Hz). A 100k resistor would be much better. The resistors needed are too small... Here, one 555 makes 10 mSec pulse at 0.25Hz to 25 Hz.

 

I really appreciate the schematic gopherT, I'll try to get the new pot, and come back with the results. Thanks for all your help guys! Also gopherT would you be able to show the math you are using to calculate the frequency values?

 

I really appreciate the schematic gopherT, I'll try to get the new pot, and come back with the results. Thanks for all your help guys! Also gopherT would you be able to show the math you are using to calculate the frequency values?

Just draw it out in a simulator and adjust values. For the turn-up ration, make sure the fixed resistor in series with your pot is just under 1% of the potentiometer. Also, get a Logarithmic (audio) taper potentiometer. When knob is pointing to you and pins are pointing down, connect the center pin to the left pin.

 

I really appreciate the schematic gopherT, I'll try to get the new pot, and come back with the results. Thanks for all your help guys! Also gopherT would you be able to show the math you are using to calculate the frequency values?

With 100:1 adjustment the pot will be a little goosie. About 15ms per degree of rotation. So you might want to consider 2 pots - a course and a fine. Or at least get a logarithmic pot to help with the short times.

 

Just draw it out in a simulator and adjust values. For the turn-up ration, make sure the fixed resistor in series with your pot is just under 1% of the potentiometer. Also, get a Logarithmic (audio) taper potentiometer. When knob is pointing to you and pins are pointing down, connect the center pin to the left pin.

Hey I wired up the schematic you showed me and im having a bit of trouble. I dont know if its quite right. I need a 25hz signal with short pulses, so it seems as though it constantly on, and need .25hz of again a short pulse, and it can be clearly seen as off most of the time, and on for short bursts. It seems like I built the opposite of that. Did I wire it incorrectly, or is that what your design is supposed to be.

 

Did I wire it incorrectly

Have you got the diode the right way round?

 

Yeah the diode is correct, but his circuit seems to adjust the duty cycle and not the frequency.

 

Not according to LTspice. Simulation shows the circuit adjusts the frequency but the pulse width stays at about 10mS. Reverse the diode and try.

 

Would you be able to show me what the simulations look like?

 

Sure. Here you go:

 

Ok, I must have a connection error then, thanks so much for your help.

 

I am still having trouble with the duty cycle, as I rotate the pot the frequency remains constant and the duty cycle goes from ~3-99%. The diode is oriented correctly, I dont know what the problem is.

 

I am still having trouble with the duty cycle, as I rotate the pot the frequency remains constant and the duty cycle goes from ~3-99%. The diode is oriented correctly, I dont know what the problem is.

Send a photo of your breadboard. Close up enough that wee can see all - multiple photos if needed.

 

Send a photo of your breadboard. Close up enough that wee can see all - multiple photos if needed.

let me know if you need anymore

 

I dont know what the problem is.

Are you measuring the pulse output between pin 3 and ground, or between pin 3 and V+?

 

pin 3 and ground, I also have an LED in the circuit.

 

let me know if you need anymore

You need one more jumper wire. The resistor connected to the red (+) power rail connects to a red wire of the potentiometer (we'll call that "NODE 1"). Add a jumper from "NODE 1" to pin 7 of the 555 timer.

NODE 1 is actually row 18 of the breadboard.

 

Wow, it works! Thanks!