audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Pin 6 of the 555 is a triangle wave that feeds an input of the comparator. It is a sensitive spot and its frequency is affected a little by the resistance and capacitance of the frequency counter in the DMM.
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Hi Allvol,
"My" 555 circuit is the classic "triangle wave into a comparator with the other comparator's input connected to a variable DC voltage" PWM circuit that usually uses a opamp integrator and a Schmitt trigger oscillator to make the triangle wave.
The 555's timing capacitor is charged and discharged symmetrically by a resistor from the 555's output pin 3. The capacitor is also connected to pins 2 and 6 for its threshold voltages and has a curved triangle wave across it.
"Your" 555 circuit with its steering diodes also works well for PWM.
"My" 555 circuit is the classic "triangle wave into a comparator with the other comparator's input connected to a variable DC voltage" PWM circuit that usually uses a opamp integrator and a Schmitt trigger oscillator to make the triangle wave.
The 555's timing capacitor is charged and discharged symmetrically by a resistor from the 555's output pin 3. The capacitor is also connected to pins 2 and 6 for its threshold voltages and has a curved triangle wave across it.
"Your" 555 circuit with its steering diodes also works well for PWM.
Hi
P1 is the 555 circuit of audioguru and measured on my MM. (Was running the fans etc.)
P2 is the “textbook version” of allvoll and as measured after replacing the 47uF cap with a .47uF cap. My MM does not read if it is to slow. Yes, I did get the LED to flash, with the 47 uF cap.
As mentioned before both circuits are working. The original 555 with the opamp and the 2 transistor, and the audioguru version are working. The fans are running OK.
Now lets get the range with the thermistor in place, where to from here?
Thanx
Virus
View attachment 39080
View attachment 39081
P1 is the 555 circuit of audioguru and measured on my MM. (Was running the fans etc.)
P2 is the “textbook version” of allvoll and as measured after replacing the 47uF cap with a .47uF cap. My MM does not read if it is to slow. Yes, I did get the LED to flash, with the 47 uF cap.
As mentioned before both circuits are working. The original 555 with the opamp and the 2 transistor, and the audioguru version are working. The fans are running OK.
Now lets get the range with the thermistor in place, where to from here?
Thanx
Virus
View attachment 39080
View attachment 39081
Allvol
I had a ball playing with the fan’s.
Did the 10k trim pot as per your diagram fan1.gif, works excellent, can get the fans down to just- just- just- turning (long pulses). I also left the other trim pot in place, between the 2 pot’s and changing the cap C2 with different values, what a range?, with some setting nice (annoying) music on the fans !
I have a question though, how much of what, here, will do the trick?
This project started out with resistors and a dip switch, because of the circuit in
I had a ball playing with the fan’s.
Did the 10k trim pot as per your diagram fan1.gif, works excellent, can get the fans down to just- just- just- turning (long pulses). I also left the other trim pot in place, between the 2 pot’s and changing the cap C2 with different values, what a range?, with some setting nice (annoying) music on the fans !
I have a question though, how much of what, here, will do the trick?
This project started out with resistors and a dip switch, because of the circuit in
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Changing the DC voltage of pin 5 on a 555 changes both the frequency and the duty-cycle of the pulses. Using the steering diodes circuit or the triangle-wave circuit changes the duty-cycle of the pulses without changing the frequency much. Then the frequency can be high enough that it isn't audible.
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
I have a permanent magnet electric motor operating its PWM at about 3kHz and it whines loudly.
If your motor has a high inductance then a low frequency should be used. It takes time for current to build up in an inductor.
If your motor has a high inductance then a low frequency should be used. It takes time for current to build up in an inductor.
Allvol
How was your golf day?
Thanks for the links, interesting info.
The best I can describe for you what I want to do is, if it is at all possible for you to build the circuit in Rely 14, 3 components only.
You can adjust the trim pot for the fans to come to a dead stop when your PC is cold, just switched on, with the thermistor in place close to the CPU heatsink, ( by playing around until you get a good position for the thermistor) it will easily control the fans from 0 % to
How was your golf day?
Thanks for the links, interesting info.
The best I can describe for you what I want to do is, if it is at all possible for you to build the circuit in Rely 14, 3 components only.
You can adjust the trim pot for the fans to come to a dead stop when your PC is cold, just switched on, with the thermistor in place close to the CPU heatsink, ( by playing around until you get a good position for the thermistor) it will easily control the fans from 0 % to
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
The circuit with only 3 parts has the Mosfet as a resistor and it gets hot. The Mosfet in a PWM circuit doesn't get hot. The difference in the cost of the parts is nearly nothing, but the simple circuit needs a big expensive heatsink.
GM, Virus
From the 4QD website: In a practical low voltage controller the switch opens and closes at 20kHz (20 thousand times per second). This is far too fast for the poor old motor to even realise it is being switched on and off: it thinks it is being fed from a pure d.c. voltage. It is also a frequency above the audible range so any noise emitted by the motor will be inaudible. It is also slow enough that MOSFETs can easily switch at this frequency.
Measure the frequency at pin 3 of your 555 without the thermistor in circuit.
From the 4QD website: In a practical low voltage controller the switch opens and closes at 20kHz (20 thousand times per second). This is far too fast for the poor old motor to even realise it is being switched on and off: it thinks it is being fed from a pure d.c. voltage. It is also a frequency above the audible range so any noise emitted by the motor will be inaudible. It is also slow enough that MOSFETs can easily switch at this frequency.
Measure the frequency at pin 3 of your 555 without the thermistor in circuit.
Last edited by a moderator:
Similar threads
