destroying my last pic? driving a miniature motor

[Michael Wakileh]

Hi everyone,
Please help me if you can....I don't want to destroy my last pic....

I'll get right on topic:
I had partial success driving a 4mm motor directly from the 4 pwms of my 16f690. I was using pulse steering to output hpwm signal on 4 pins. Testing this, I realized that this would not allow me enough current on the motor i am using.

Here's what I did initially:
I chose 250 ohm resistors for each pwm output because 5v/250ohm is 20 mA the max a pic can source or sink. After the resistor these lines converged going to the positive terminal of the motor. Because I gave moter 4 pwm signals, the resistance to 5v(supplied by PWM) was actually 250/4=62.5ohm.
My motor has 9.6ohm internal resistance
62.5ohm divider: 9.6/9.6+62.5ohm x 5V==>motor was only getting .666v….
Current through the motor 5v/72.1ohm = 69.3mA
This was not enough to get it spinning nicely...


Here's where I destroyed 2 pics:
I quickly tried hooking up one of the 4 pwm signals through a 2n2222 to
boost the current. Although i thought i had enough protection using diodes when I ran the program, not much happened... Also some sensors on i2c and power lines didn't blink as they normally do at startup. Only removing the pic 16f690 got those sensors blinking again. After adding some more diodes, safer resistor values I tried again with another pic....Same result... Unfortunately I can not reproduce the exact schematics as it was 5am and I was tired a little impatient and yes...drinking...
I think I may have left the other pwm pins floating, or possibly switched the collector and emitter. All I know is that I didn't even get to see smoke...


Can anyone advise me on a lowest partnumber/smallest parts solution that would do the beforementioned. HERE IS WHAT I HAVE IN MIND...

[Darrel Taylor]

That diagram's a little hard to follow.
Does this look like what you were thinking of?

<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1913&stc=1&d=118631783 1">

Hope not.
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[Darrel Taylor]

With a 2N2222A, here's what I think would work.

<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1915&stc=1&d=118632654 6">

If you don't have a good, solid, well filtered power supply, the PIC will have problems. Resetting, or just doing weird stuff.

And the motor's proximity to the circuit, may have the same effect.
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[Michael Wakileh]

Thanks Darrell... you always come to the rescue.... I will try this out tomorrow. You redrew my schematic nicely, but I did have the emitter going to ground (btw, which program do you use?)... Is there a difference in connecting the load between emitter and ground, or between collector and vdd (besides resistance increasing base to ground when the load is on the emitter side)? For power I try to stay mobile. Here I used just a 9V battery, 7805, 100nFcap, and an electrolytic cap.... Eventually I will be using 4 or 5 of these motors and probably a seperate power supply...

[mikendee]

Have you had a look at the MicroChip app note AN 893 . Hopefully it might be of some help.

This should be the link to it.
http://www.microchip.com/stellent/id...pnote=en012134

[Darrel Taylor]

Is there a difference in connecting the load between emitter and ground, or between collector and vdd (besides resistance increasing base to ground when the load is on the emitter side)?

With transitors, the current you get out is dependant on the current from the base to emitter. If the voltage on the emitter changes, then the base to emitter current will be reduced. So if the load is between the emitter and power, ... as the transistor starts to conduct, the emitter voltage changes and counteracts the base current that's trying to turn it on. While it seems to kinda sorta work a little bit, you always end up with a lower current output.

So basically, you want the emitter to be at a constant voltage, either GND or V+.

But the difference is ... if you want to "source" current to the load from V+ (like in the first schem.) you would use a PNP transistor. Then output HIGH from the PIC is OFF, and LOW is ON.

And as I read this back, it doesn't even make sense to me. (I'm a software guy).

Alain!!! Help!!!! Anybody!!!

[Archangel]

Thanks Darrel,
I have seen it in print that the transistors should go one way but not the other, but never an explanation as to why.
Thanks!

[Acetronics2]

And as I read this back, it doesn't even make sense to me. (I'm a software guy).

Alain!!! Help!!!! Anybody!!!

Hi, Darrel

For simplicity :

1) Motor ( or load ) has one terminal connected to GROUND

- use a PNP Transistor w/Emitter to POwer ( or P- Mosfet W/ Source to Power ). the "ON" state will be with a LOW state from the PIC.

2) Motor has one terminal Connected to POWER

- use a NPN Transistor W/Emitter to GRound ( or N Mosfet w/ Source to GRound ). the "ON" state will be with a HIGH state from the Pic.


That's all !!!

Alain

[rhino]

...You redrew my schematic nicely

Darrel.... what do you use for schematic drawings?

[Darrel Taylor]

Darrel.... what do you use for schematic drawings?

I guess I forgot to answer that part.
Or maybe I was unconsciously avoiding it, since the program I use is a constant source of mental anguish.

I use IVEX WinDraft/WinBoard.

Ivex went out of business a couple years ago, and now there's no one to fix all the bug's.
Which is probably why they went out of business in the first place. (there's a lot of bug's).

And when the company closed, so did it's online Auto-Router server.
So now everything has to be routed manually. And of course that's hard to do because of the Bug's.

The last board I did, ... 18F6720, 10 other chips, 101 resistors,35 capacitors, etc. took almost 2 months to route manually.

I've got to find another program. And PCB123 just doesn't do it for me.
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