Hi
Im new to the site and building circuits
Ive begun with building a pwm controller but have hit a issue that I was hoping to find some help
The motor runs fine when I plug the battery to it the only problem I'm having is that i cant seem to get my 10k resistor to vary the speed of the motor .
Ive checked the 555 timers with a oscilloscope and I'm getting a square wave out of the pin 3 along with this I've done continuity test with the multimeter all seems very fine.
Any help will be great
thanks

 

Welcome to AAC.

Schematics are the language of electronics, so please post one so we can better answer your questions.
Otherwise about all we can do are wild guesses, since we have no idea where this 10k pot is located.

 

Hi again I do apologise for the late reply with the schematic and design.
As I said first , I am getting square waves out of my 555 timers I'm just not able to the 10k resistor to vary the speed of the motor
Thanks !

 

Unfortunately I'm unable to change the circuit , I have to complete with following that schematic .

 

Hello,

Is the potentiometer in working order and correctly connected?
You could add one simple connection to avoid an open contact:



Bertus

 

Yes the potentiometer works and this is how I've connected which I believe is correct ?

Hello,

Is the potentiometer in working order and correctly connected?
You could add one simple connection to avoid an open contact:

View attachment 125189

Bertus

 

Hello,

When you bend the loose piece of wire to the connection of the potentiometer and solder it there, you can avoid an open connection:



Bertus

 

Hello,

When you bend the loose piece of wire to the connection of the potentiometer and solder it there, you can avoid an open connection:

View attachment 125215

Bertus

Hi
I've just connected that terminal to the end one and there is still no change

 

Unfortunately I'm unable to change the circuit , I have to complete with following that schematic

Why? Is this a school/college assignment?

 

Why? Is this a school/college assignment?

It was but not anymore because it never worked so I decided to keep it so I brought it back because it's stumped me why it still isn't working

 

It's not working because the output of U2 is holding the Trig input of U1 low for ~half of the U1 oscillation period.

 

It's not working because the output of U2 is holding the Trig input of U1 low for ~half of the U1 oscillation period.

Is there nothing I can do to sort that ?

 

Hello,

Add two components between the 555's to have shorter trigger pulses as @Alec_t suggested:



Bertus

 

Hello,

Add two components between the 555's to have shorter trigger pulses as @Alec_t suggested:

View attachment 125234

Bertus

I add the components to the circuit , didn't fix the circuit ... also all that occurred was an overheating on the U2 555 .

 

Hello,

I guess I took the capacitor too large.
Have a look at the several schematics in the attached PDF how an 555 gets triggered.

Bertus

 

You can eliminate the RC at the output of U2 if you change U2 to give a short negative pulse out.
This can be done by eliminating R1 (replace with a short) and increasing R2 to about 1.5kΩ (or a value to get the astable frequency you want).
The negative output pulses will then be just several microseconds (≈8μs in my simulation) in width, which is long enough to trigger U1, but not long enough to interfere with U1's output pulse width.

Here's an LTspice simulation of that: