ok so i just built this circuit here:
Pulse Width Modulation - Electronics in Meccano
but i made a few changes to accommodate some things...
1. "frequency preset" pot is a 100k
2. 0.1uF cap on the first timer (connected to frequency pot) is changed to 0.015uF
3. delete 1k output resistor on the second timer
4. Replace the TIP31C with an IRF640
5. Have the source of the IRF640 connected to ground, and the gate is connected directly to the output of the second 555
6. Have the motor and diode in the diagram moved up to be between the +12v and the drain of the IRF640
7. I used a NE556 instead of 2 NE555's
8. caps connected to pin 5 are 0.015uF since i didn't have any 0.01uF's on me
Ok so here's the problem...it all turns on, but i get no pwm. I unfortunately don't have a scope so i can't see if i'm getting any oscillation. The motor spins at full speed and no matter how much i turn the "speed" pot, i don't get any change in motor speed at all. I used my multimeter on the DCv setting to check the output pin on the second 555 but all it shows me is 12v....with pwm i should be able to use a multimeter cause the meter will be able to see the average voltage caused by the duty cycle of the pwm correct? like if i had the duty cycle set at 50% my multimeter would read roughly 6 instead of twelve....anyways, the voltage at the output didn't change what-so-ever...just a steady 12v....
for the mosfets, they are brand new and i found on one of them that the Dsr was effectively open circuit, while the other was infinite resistance on my meter....tested them both out on my pwm circuit and i got the same results with each one.
One thought i had was that the output voltage from the oscillation stage was too high for the input of the pwm stage? I would be putting ~12v or so to the input of the second 555....
any help ppl????
Pulse Width Modulation - Electronics in Meccano
but i made a few changes to accommodate some things...
1. "frequency preset" pot is a 100k
2. 0.1uF cap on the first timer (connected to frequency pot) is changed to 0.015uF
3. delete 1k output resistor on the second timer
4. Replace the TIP31C with an IRF640
5. Have the source of the IRF640 connected to ground, and the gate is connected directly to the output of the second 555
6. Have the motor and diode in the diagram moved up to be between the +12v and the drain of the IRF640
7. I used a NE556 instead of 2 NE555's
8. caps connected to pin 5 are 0.015uF since i didn't have any 0.01uF's on me
Ok so here's the problem...it all turns on, but i get no pwm. I unfortunately don't have a scope so i can't see if i'm getting any oscillation. The motor spins at full speed and no matter how much i turn the "speed" pot, i don't get any change in motor speed at all. I used my multimeter on the DCv setting to check the output pin on the second 555 but all it shows me is 12v....with pwm i should be able to use a multimeter cause the meter will be able to see the average voltage caused by the duty cycle of the pwm correct? like if i had the duty cycle set at 50% my multimeter would read roughly 6 instead of twelve....anyways, the voltage at the output didn't change what-so-ever...just a steady 12v....
for the mosfets, they are brand new and i found on one of them that the Dsr was effectively open circuit, while the other was infinite resistance on my meter....tested them both out on my pwm circuit and i got the same results with each one.
One thought i had was that the output voltage from the oscillation stage was too high for the input of the pwm stage? I would be putting ~12v or so to the input of the second 555....
any help ppl????