PWM Controller - Problem

[RiccardoR]

Hi there
I'm new to the site and building circuits
I've completed building a PWM Controller , I'm getting square wave out of the pin 3 from my 555 timers and the motor is spinning but the 10k pot isn't varying the speed of the motor this is my only issue , and I'm unsure how to resolve it
Any help would be great
Thank you !

 

[JimB]

Welcome to ETO.

Sorry but we are not psychic, please post a copy of the schematic of your PWM controller, then we can consider what may be wrong.

JimB

 

[RiccardoR]

 

[dr pepper]

Welcome here.
I think you have somethign wrong around U1, double check all your connections on this chip.
If you know you have a square wave then I assume you have access to a 'scope, if so check the o/p of U1, its pulse width should change as you vary the pot, speaking of which the wires to the pot should be connected to one of the outer pins and the centre.

 

[RiccardoR]

Thanks for the advice , I'll test output of U1 tomorrow .
If the pulse width doesn't change what can I look to do to resolve this situation
Also the pot is the connected with one outside and inside terminal .. the final terminal is left untouched

Welcome here.
I think you have somethign wrong around U1, double check all your connections on this chip.
If you know you have a square wave then I assume you have access to a 'scope, if so check the o/p of U1, its pulse width should change as you vary the pot, speaking of which the wires to the pot should be connected to one of the outer pins and the centre.

 

[Ian Rogers]

Driving a motor via PWM isn't linear.... The PWM on the second 555 cannot be a smaller ratio than the pulse from the first 555 so try and make the generated pulse as small as possible...

I think that the pulse is big enough to give nearly full speed so the control is not available.

Try and change the 420 ohm with a 100 ohm and see if you get more control.. As a plan B... Use Alex's PWM here

https://www.electro-tech-online.com/articles/simple-pwm-control.528/
Or Crutchow's here
https://www.electro-tech-online.com...buffer-output-requires-only-5-components.799/

 

[RiccardoR]

Driving a motor via PWM isn't linear.... The PWM on the second 555 cannot be a smaller ratio than the pulse from the first 555 so try and make the generated pulse as small as possible...

I think that the pulse is big enough to give nearly full speed so the control is not available.

Try and change the 420 ohm with a 100 ohm and see if you get more control.. As a plan B... Use Alex's PWM here

https://www.electro-tech-online.com/articles/simple-pwm-control.528/
Or Crutchow's here
https://www.electro-tech-online.com...buffer-output-requires-only-5-components.799/

Hi
I'm currently on the oscilloscope now .
I've noticed that I'm getting a square wave out of pin 2 on u1 555 timer not out of pin 3 ?

 

[Colin]

Basically, the way to look at the 1k on the base of the output transistor is this:
The transistor will divide the resistance of the base resistor by 100 (the gain of the transistor) and the transistor can be replaced by a 10 ohm resistor. Do you want a 10 ohm resistor in series with the motor?????
You can get a much simpler PWM circuit using one 555.

 

[Ian Rogers]

I've noticed that I'm getting a square wave out of pin 2 on u1 555 timer not out of pin 3 ?

The square wave is coming from U2.. If there is no output from pin 3 then a) circuit built incorrectly b) you've blown it..

 

[dr pepper]

Ricardo, U1 isnt triggering, the wave your looking at is from U2, if all your connections are correct you might need to replace U1.