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cromiumlake

DC Motor PWM (SLAA120)

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Hi There,

 

I am testing the circuit that appears on Slaa120 (PWM DC Motor Control Using Timer_A of the MSP430), of course with some small modifications.

?I made the Darlington pair using 2N3904 transistors, the resistor is 1200ohms.

To test the circuit, I connect the base to 5v and...the motor spins.

In the other hand the code for PWM is working and I can test it on P1.6, I can see the LED on.

 

My problem is that if I join the two parts, the motor does not spin (I connect the base to P1.6). I can only think that the MSP is not giving me enough power, but the 2N3904 does not need much.

Any ideas,

 

Cromiumlake

 

post-30510-0-17962200-1368702183_thumb.png

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No - you don't want to use an internal resistor here.  Pull-ups/down are typically used when you're using buttons - they keep the pin value at a 1 or 0 until the button connects the pin to vcc or gnd.  

 

I'd suggest a couple of tests - try a lower value resistor (two in parallel will 1/2 your resistance if you don't have other values available).  Also - try just turning the pin on and off - have you already tried connecting 3.6v from the LP to the base?  That will let you eliminate PWM as your possible problem.

Another possibility - swap your motor with an LED.  

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No - you don't want to use an internal resistor here.  Pull-ups/down are typically used when you're using buttons - they keep the pin value at a 1 or 0 until the button connects the pin to vcc or gnd.  

 

I'd suggest a couple of tests - try a lower value resistor (two in parallel will 1/2 your resistance if you don't have other values available).  Also - try just turning the pin on and off - have you already tried connecting 3.6v from the LP to the base?  That will let you eliminate PWM as your possible problem.

Another possibility - swap your motor with an LED.  

Thanks for the tests, nice approach to troubleshooting.

 

I dis the following tests:

470 ohms = fail

10  ohms = fail

replace motor with led: just by touching the resistor the led goes on. If connect to Vcc goes on. If plugged LP ground does on. If Connected to anything goes on

 

Now, I just don't get it hhahahha

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Hm - how about the motor with the transistor base @ 3.6v?  Looks like you tried that with the LED, but I'm not sure from your motor results.

 

Do you know what kind of current your motor needs?  2n3904 is only rated for 200mA

 

The motor requires 5V at 0.16A

how about the motor with the transistor base @ 3.6v?....R: Dit not work, that settup is when I tried the 470 and 10 ohms

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Hm - 3.6v should be enough with the lower base resistor - do you have another transistor to try out?  I fried some 3904's the other day because my resistor was too low.  

 

But, if it was fried would not work when connected directly to 5v line

Please the attached picture and tell me what you think

post-30510-0-20328100-1368719483_thumb.jpg

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Hm - think I might see it.  Do you have a connection between the GND of the LP and your power supply connected?

 

 

IT works!!!.....When I give it a large enough duty cycle :)

I don't know who decided to put me as an "Advanced Member"...?I'm certainly not

sorry for the noise

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Awesome!  Didn't think about the power supply.  

I believe the "advanced member" is based the number of posts you have.  Something the forum automatically does.  

 

And no worries about the questions - I'm not an EE - I had the same kinds of questions when I started.

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