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Electronics => Electronics => Topic started by: yash25 on July 25, 2009, 11:04:42 PM

Title: Doubt about P89V51 and L293D.
Post by: yash25 on July 25, 2009, 11:04:42 PM

Im making a multipurpose board of the Philips P89v51 , I had the following doubts...
1) Do i connect pullup resistors only to the PORT0 or to all the ports... a book i read recently tells me that PORTS1,2,and3 have inbuilt resistors.

A doubt about the L293D
2) What will happen if I connect the 12V point in the L293D chip, to a 5V source? Will the motors run slowly?

Title: Re: Doubt about P89V51 and L293D.
Post by: Joker94 on July 26, 2009, 05:29:22 AM

1) to find out what pins have pull up resistors do a google search on your chip and you should be able to find a data sheet, That should tell you. You may be able to find it off the phillips web site.

2) It depends on the voltage rating of the motor. If you pass regulated 5 V through a 6v motor it will run slower. And remember, the more current the higher the torque. I am not sure what the regulator will do to the current.

Title: Re: Doubt about P89V51 and L293D.
Post by: SmAsH on July 26, 2009, 06:13:58 AM

motors will draw a set amount of current depending on their load.
if a regulator cant output enough current it will burn out.

Title: Re: Doubt about P89V51 and L293D.
Post by: yash25 on July 27, 2009, 05:34:05 AM

Quote from: Joker94 on July 26, 2009, 05:29:22 AM

2) It depends on the voltage rating of the motor. If you pass regulated 5 V through a 6v motor it will run slower. And remember, the more current the higher the torque. I am not sure what the regulator will do to the current.

The Voltage rating of the motors is 3V...so then what will happen in this case, if i apply 5V, to the 12V pin of my L293D IC ...will the motors run slower?

Title: Re: Doubt about P89V51 and L293D.
Post by: SmAsH on July 27, 2009, 05:42:18 AM

by "12V pin" do you mean the motor supply voltage?

Title: Re: Doubt about P89V51 and L293D.
Post by: yash25 on July 27, 2009, 11:46:07 AM

I dunno..but there is a pin in the L293D IC which goes to a 12 V source... pin number 8 of the IC...

Title: Re: Doubt about P89V51 and L293D.
Post by: SmAsH on July 27, 2009, 02:29:48 PM

thats motor supply voltage, you put your motors battery pack there.

Title: Re: Doubt about P89V51 and L293D.
Post by: yash25 on July 28, 2009, 11:15:49 AM

so if the rating of the motors is 3 volts and my supply voltage is 5 Volts...then will my motors work if i give this supply to the pin number 8 of the L293D, and the o/p of the l293D to my motors?

Title: Re: Doubt about P89V51 and L293D.
Post by: SmAsH on July 28, 2009, 03:42:33 PM

ideally you should be giving 3v to pin 8.. 5v may burn it out over time.
i did not understand your second question ???