Running out of PWM outs on PIC16F876A - Electronic Circuits Projects Diagrams Free

raitl · 24th February 2006, 05:30 PM

I want to run two cordless drill motors through MC33886DH-s with PIC16F876A. The MC33886DH uses two inputs to control the direction of the motors, but the PWM is applied to the pin, that is LOW at the time. So when running in one direction, I need to PWM on pin, when running in reverse - another. And since I want to run 2 motors, I'd need 4 PWM outs. Is there any other way to solve the problem, aside from getting a new pic?

Someone Electro · 24th February 2006, 06:47 PM

Simple you dont drive it directly whith PWM.

You use PWM to pullwon 2 normal I/O pins

raitl · 24th February 2006, 06:53 PM

but I need to PWM two pins alternately.

Say I use PinA and PinB for controlling one motor. So when moving forward, I'd keep PinA HIGH and PWM PinB. And for reverse I need to hold PinB HIGH and PWM PinA.

justDIY · 24th February 2006, 06:57 PM

look through the microchip website at some of the larger 18F series chips ... many of them have "motor control" modules, called ECCP or Enhanced Capture Compare PWM, where the PMW module is capable of driving multiple H-bridge chips in various configurations (more pwm outputs)

raitl · 24th February 2006, 07:00 PM

yeah well that's what I wanted to know... if there was any other way, except changing PIC's.. So I guess I'm going to have to look for an alternative H-bridge for my motors.

raitl · 25th February 2006, 06:13 AM

ok..I started wondering something... I would be set, if there was a way to switch I/O-s with an extra logic gates or something like that.

Or maybe with a couple of transistors? Create a low power H-bridge, use PIC PWM pin for one input, take +5V for the other and a second PIC pin to control the direction of the small H-bridge? That could work, couldn't it?

**Nigel Goodwin** · 25th February 2006, 08:29 AM

The usual way is to apply the PWM to an 'enable' input on the H-bridge, and use either one or two I/O lines to set the direction - most small H-bridge IC's have this facility!.

Basically you need to design your H-bridge accordingly, the two PWM channels should be all you need!.

raitl · 25th February 2006, 08:41 AM

Quote:

Originally Posted by Nigel Goodwin

The usual way is to apply the PWM to an 'enable' input on the H-bridge, and use either one or two I/O lines to set the direction - most small H-bridge IC's have this facility!.

I know that, and the other two H-bridge IC's I have, both have that facility. But the 5Amp one that I need to use, is different at that.

**Nigel Goodwin** · 25th February 2006, 09:02 AM

Quote:

Originally Posted by raitl

Quote:

Originally Posted by Nigel Goodwin

The usual way is to apply the PWM to an 'enable' input on the H-bridge, and use either one or two I/O lines to set the direction - most small H-bridge IC's have this facility!.

I know that, and the other two H-bridge IC's I have, both have that facility. But the 5Amp one that I need to use, is different at that.

I still think that's FAR too small anyway! :lol:

raitl · 25th February 2006, 11:29 AM

well if they crash and burn on me, then I'll get some high power MOSFETS and put together a new H-bridge. But since these are the options I have right now, I'll have to find a way to get the job done with those IC-s.

Someone recommended to use 74HCT00-s to toggle the PWM and the second PIC output. But I have no idea how to accomplish that...

ops:

Someone Electro · 25th February 2006, 11:56 AM

Its simple look have two normal I/O pins drive the H brihgt trough a resistor. Then have an diode to the PWM pin.So the at the PWM signal will pull down the I/O pin.So you make the I/O go high an the PWM will pul it down trough the diode.

This is the simplese way to drive an H bridge whith no enable fuction.

An more profesional method would be AND gates.

Someone Electro · 25th February 2006, 12:02 PM

Heres an schem

raitl · 25th February 2006, 02:06 PM

ok, so this should work?

SL1 and SL2 - motor outs
SL3 - motor and H-bridge power
SL4 - +5V power
SV1 - to PIC

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24th February 2006, 05:30 PM	(permalink)
raitl	Running out of PWM outs on PIC16F876A I want to run two cordless drill motors through MC33886DH-s with PIC16F876A. The MC33886DH uses two inputs to control the direction of the motors, but the PWM is applied to the pin, that is LOW at the time. So when running in one direction, I need to PWM on pin, when running in reverse - another. And since I want to run 2 motors, I'd need 4 PWM outs. Is there any other way to solve the problem, aside from getting a new pic? __________________ Here...let me improve it for you! Puff of smoke ....oops...

24th February 2006, 06:47 PM	(permalink)
Someone Electro	Simple you dont drive it directly whith PWM. You use PWM to pullwon 2 normal I/O pins __________________ Il give you shocking experience.

24th February 2006, 06:53 PM	(permalink)
raitl	but I need to PWM two pins alternately. Say I use PinA and PinB for controlling one motor. So when moving forward, I'd keep PinA HIGH and PWM PinB. And for reverse I need to hold PinB HIGH and PWM PinA. __________________ Here...let me improve it for you! Puff of smoke ....oops...

24th February 2006, 06:57 PM	(permalink)
justDIY	look through the microchip website at some of the larger 18F series chips ... many of them have "motor control" modules, called ECCP or Enhanced Capture Compare PWM, where the PMW module is capable of driving multiple H-bridge chips in various configurations (more pwm outputs)

24th February 2006, 07:00 PM	(permalink)
raitl	yeah well that's what I wanted to know... if there was any other way, except changing PIC's.. So I guess I'm going to have to look for an alternative H-bridge for my motors. __________________ Here...let me improve it for you! Puff of smoke ....oops...

25th February 2006, 06:13 AM	(permalink)
raitl	ok..I started wondering something... I would be set, if there was a way to switch I/O-s with an extra logic gates or something like that. Or maybe with a couple of transistors? Create a low power H-bridge, use PIC PWM pin for one input, take +5V for the other and a second PIC pin to control the direction of the small H-bridge? That could work, couldn't it? __________________ Here...let me improve it for you! Puff of smoke ....oops...

25th February 2006, 08:29 AM	(permalink)
Nigel Goodwin	The usual way is to apply the PWM to an 'enable' input on the H-bridge, and use either one or two I/O lines to set the direction - most small H-bridge IC's have this facility!. Basically you need to design your H-bridge accordingly, the two PWM channels should be all you need!. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

25th February 2006, 11:29 AM	(permalink)
raitl	well if they crash and burn on me, then I'll get some high power MOSFETS and put together a new H-bridge. But since these are the options I have right now, I'll have to find a way to get the job done with those IC-s. Someone recommended to use 74HCT00-s to toggle the PWM and the second PIC output. But I have no idea how to accomplish that... ops: __________________ Here...let me improve it for you! Puff of smoke ....oops...

25th February 2006, 11:56 AM	(permalink)
Someone Electro	Its simple look have two normal I/O pins drive the H brihgt trough a resistor. Then have an diode to the PWM pin.So the at the PWM signal will pull down the I/O pin.So you make the I/O go high an the PWM will pul it down trough the diode. This is the simplese way to drive an H bridge whith no enable fuction. An more profesional method would be AND gates. __________________ Il give you shocking experience.