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PWM Controller - Problem

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RiccardoR

New Member
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

Super Moderator
Most Helpful Member
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
 

dr pepper

Well-Known Member
Most Helpful Member
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

New Member
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

User Extraordinaire
Forum Supporter
Most Helpful Member
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

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

RiccardoR

New Member
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

http://www.electro-tech-online.com/articles/simple-pwm-control.528/
Or Crutchow's here
http://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

Active Member
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.

PWM-Controller.gif

MotorPWM.gif
 

Ian Rogers

User Extraordinaire
Forum Supporter
Most Helpful Member
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

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