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Motor browning out PIC

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Motor browning out PIC

Postby JoshMac » Fri Mar 25, 2016 4:39 am

Hi guys,

What capacitor would I need to stop a small 12vDC motor (250ma loaded) from browning out a PIC controller?
The motor is controlled with a L293D controller.
PSU is a 12v 5A power supply, the project is not in the situation to be able to have 2 power supplies sadly.

I know a capacitor is probably needed for the motor, but I am unsure as to the value or type of capacitor needed.

Help and advice is, as always, greatly appreciated.
Kind regards,
Josh
JoshMac
 
Posts: 27
Joined: Sun Dec 23, 2012 4:59 am
Location: Perth, Western Australia

Re: Motor browning out PIC

Postby pebe » Fri Mar 25, 2016 3:44 pm

Hi Josh,
Are you using a 5V regulator for the PIC, fed from the 12V supply?
pebe
 
Posts: 1058
Joined: Tue Dec 09, 2003 11:12 pm
Location: Ellon, Scotland

Re: Motor browning out PIC

Postby JoshMac » Sun Mar 27, 2016 2:52 am

I am, a 7805, I have also tried adding a delay in the pic routine between changing directions.
I have tried to upload a circuit diagram, but the site is saying "The image file you tried to attach is invalid", I've tried with png, jpg and bmp. So here is a link to the diagram on google drive.
https://goo.gl/QtPS0Z

Regards,
Josh
JoshMac
 
Posts: 27
Joined: Sun Dec 23, 2012 4:59 am
Location: Perth, Western Australia

Re: Motor browning out PIC

Postby pebe » Sun Mar 27, 2016 9:59 am

I suggest you fit a 10µF to 100µF cap across the 5V output of the 7805 and a diode in series with the 12V feed into it.
When the 12V suddenly reduces due to a high motor current surge, the diode will cut off but the cap will maintain the voltage supply to the PIC.

I'm sorry that you cannot upload a picture. It is due to a glitch in the site's software and it's not something I have control over. I have tried every conceivable way to contact Admin about it, but without success. He last visited the site in August last year, so he has either abandoned the site or is sick - or worse!
pebe
 
Posts: 1058
Joined: Tue Dec 09, 2003 11:12 pm
Location: Ellon, Scotland

Re: Motor browning out PIC

Postby JoshMac » Mon Mar 28, 2016 2:26 pm

Hi Pebe,
I added the cap on the output of the 7805 and it all works a treat. Thanks for your help again!
Side note: I have contacted the site owner via email and they have just fixed the upload problem!
(this is what I was trying to upload, just to test it all)
circuit.jpg
circuit.jpg (78.44 KiB) Viewed 22200 times


Kind regards,
Josh
JoshMac
 
Posts: 27
Joined: Sun Dec 23, 2012 4:59 am
Location: Perth, Western Australia

Re: Motor browning out PIC

Postby pebe » Mon Mar 28, 2016 3:03 pm

Hi Josh,

I'm glad it worked OK for you.

Admin has advised that the uploading problem has now been sorted - thanks to you.
I tried everywhere to find his email address, though - without success.
pebe
 
Posts: 1058
Joined: Tue Dec 09, 2003 11:12 pm
Location: Ellon, Scotland


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