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PWM DC Motor Control

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How do I measure the resistance of motor? Do I need to have a current flowing through it or something?
I used a multimeter, but I think I was showing up as only 5 or 6 Ohms, unless I'm reading it wrong (I was using the '200' setting).

Thanks
 
The battery is giving 7.8v on it's own.
When under load, it only supplies about 3.5v, which is not enough for the 6v motor
I guess that's the problem then...
 
The upper pot is for fine tuning to gain 100% PWM. You might as well omit it.

ah, cool.

actually i'd been looking for a schematic like that a few days ago (dual 555 ICs for better pwm) and couldnt find it from anywhere... was looking for a 0-100%, as with one 555 you can only get something like 5-95%, so thanks. i find that 5-95 is okay for what I'm doing though, but i might breadboard that thing up and look at it with a scope just for fun.

but first i have to find a way to make the scopes we have in our labs stabilize. at the max or min settings on my single 555, the waveform on the screen was jumping all over the place, you could tell there were dips where it was off, but the scope couldnt "hold it still." does the circuit get unstable at very low/high duty cycle settings or something, that makes the frequency jump around thus making it hard to read?
(sorry to hijack... ignore me)


and @Mark: do you have a stable DC supply you could access to test your circuit? batteries are... unstable. first try getting a new 9V, if that doesnt work you're gonna want a better source of power that you can depend on so you can troubleshoot your circuit better.
 
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Would a C559C or a C547B do it? They seem better than the BC548, but I'm not all that good at reading datasheets yet.
 
this is how its work
IR signal -> PIC18F452 ->L293D -> DC motor

so i wondering how the program in PIC should be written
because both also a analog input and output

thanks guys
 
this is how it works

IR signal -> input pic18f452 output -> L293D -> DC motor

i don know how to write the c PROGRAM
because both also analog in and output
thanks guys
 
Hi Mark,

you need to get a power supply which supplies a reliable current of say 1A at least. Hook up the motor and take care of sufficient spike suppression.

Use 10 to 47nF capacitors from the positive and negative motor terminals to the motor case.

Trying to "read" what's going on at the motor using an oscilloscope will fail since the back EMF of the motor will "spoil" the result.

Reading at the base of the drive transistor (or the timer output pin) you should get a good result reading the duty cycle.

I do not recommend using a bipolar transistor to drive the motor. A MosFet (N-channel) has a typical ON-resistance of a fraction of an Ohm, hence almost no voltage loss.

Even using a BUZ10 (which is overkill to the power of 10) the circuit should work under any conditions. Up to 3A motor current it won't even require a heatsink.

Boncuk
 
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