pulse width frequency modulator

[scroughstock]

Where can I find a pulse width frequency modulator I'm looking for something in 15A range, but with only 10-250 Hz frequency range. All of the modulators I have found are much higher frequency.

 

[MikeMl]

I understand "pulse width modulator" or "frequency modulator", but what is a "pulse width frequency modulator"???

 

[scroughstock]

Sorry,
I meant a PWM with adjustable adjustable power and frequency. I would like to have the freqency much lower than the others that I have found listed.

 

[MikeMl]

What is the input? Turning a pot? Control voltage?

What does it have to switch? Motor? What voltage?

 

[blueroomelectronics]

It's for the OPs previous thread. Coil & Piston engraver.

 

[RMMM]

IF you want Pulse Wave Modulation And Pulse Frequency Modulation, you can have both.

TI sells power supply switcher ICs that have both.

Are you sure of what you want? Is it for motor speed control?

 

[MikeMl]

It's for the OPs previous thread. Coil & Piston engraver.

Then why start a new thread?

 

[scroughstock]

Blueroom is correct,
No, it will not have a motor. I need to be able to adjust pulse going to an elctromagnet or coil. When this coil pulses it will drive a permanent magnet away from it. When the pulse is turned off it will allow the permanent magnet to return because there is another coil below the permanent magnet pushing back up.

No, I'm not exactly sure of what I want because I have absolutely no background electronics. That's why I came here for help.

I started a new thread because I thought it was kind of a different subject. I was asking for help to build it before, this ttime I was asking about different parts.

I would like an output of 12V DC @15A. My input would likely be be a 110V with what I think would be a transducer to feed the circuit with 12V DC.

 

[Mosaic]

Depending on the PIC u are using u can do software PWM or HW PWM if your PIC has a PWM peripheral.

Software PWM can handle the low frequencies ok. Perhaps with a 0.25 mS interrupt to drive it. The interrupt dictates the discrete interval of your PWM.

So a .25 ms interrupt can give u 1-80 steps to have a 50Hz PWM. Thus u can vary the PWM in steps of 1/80 if that's accurate enough.The 80*.25 = 20ms period. For a 250 Hz your period is down to 1/250 sec = 4 ms. To have decent PWM steps a .25 mS interrupt will give u about 16 steps at 250Hz. I'd advise running at least a 8Mhz MCU for this to handle the asm overheads.

Basically the higher the freq the larger the PWM control steps unless u up the MCU frequency to allow faster instruction execution.

Higher freq. PWM really needs u to use the HW PWM peripheral.

 

[scroughstock]

Ok,
Mosaic, You are way above me there. After doing some more reading I don't think a pulse width modulation would be the right way to go. But, I might be on to something with a pulse frequency modulation.
Does this look like it could be what I am looking for? I know I would have to change out some parts to get the power output I am looking for.
My next question would be, Can a trigger switch like from a codless drill take the place of the potentiometer?

 

[RMMM]

If it is a variable switch, then it is a potentiometer.

You will have to see what the range is on the drill-switch to see if the resistance range matches or atleast covers what you need.

You can go to Radio Shack and get yourself a few POTs for a dollar or two.

 

[riccardo]

Adjustable frequency PWM

Hi, It sounds to me like you want an adjustable frequency PWM. I've use these **broken link removed** for controlling electromagnets. You can fit a capacitor into it to give you the low frequency range you need. They have one rated for 12V 14A.

 

[scroughstock]

Perfect, Thanks Riccardo