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Gary D.
08-16-2005, 11:53 PM
I am constructing a project that involves one 12Vdc Automotive relay.

My question is.... Will a·NPN Switching transistor be able to provide enough current for the relay?

or do i just use a smaller relay?

Thanks,

Gary D.

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There are 10 kinds of people....

Those who know binary and those who Don't.

Chris Savage
08-16-2005, 11:58 PM
Gary,

·· Your choice of transistor will depend on the current the relay requires.· You could also use a MOSFET, or you could use the ULN2803.· Any of these can control the relay with the BASIC Stamp.· The MOSFET will most likely control it without issue.· The ULN2803 probably will too.· Knowing the current will tell if·a simple transistor will work.


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Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)

Beau Schwabe (Parallax)
08-17-2005, 12:33 AM
Gary,

Here is a link to an article I posted some time ago that referred to motors and determining the correct transistor and the current limiting resistor to the base of the transistor.
Just substitute the Relay for the Motor in the below application note.

http://forums.parallax.com/attachment.php?attachmentid=37701

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Gary D.
08-17-2005, 12:58 AM
Relay found Here (http://www.allelectronics.com/cgi-bin/category.cgi?category=500700&item=RLY-396&type=store)

Man i have a brain freeze. to my knowledge... The coil Resistance is 90 Ohms. Being a 12 vdc relay... that would imply a current

of ~ 133 mA. That just doesnt sound right to me... but then again i have a brain freeze...

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There are 10 kinds of people....

Those who know binary and those who Don't.

Chris Savage
08-17-2005, 01:19 AM
Gary,

·· That current sounds right to me.· And you could use a simple 2N2222 transistor to turn it on/off.· Use a 1K resistor from the Stamp I/O pin to·the Base of the transistor.· Emitter to ground.· Collector to the relay coil.· The other side of the relay coil to +12V.· Now, there should also be a diode (1N4001 or similar) across the relay coil such that the Cathode is toward the +12VDC.· Make the Stamp I/O pin HIGH, and the relay turns on.· LOW and it's off.· Enjoy!




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Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)

Gary D.
08-17-2005, 03:34 AM
Great ill be sure to Post The Final project in the Projects Section....

Stay tuned !!!

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There are 10 kinds of people....

Those who know binary and those who Don't.

jeffrey morris
08-17-2005, 07:14 AM
If I want to use a 6VDC motor, how do I find out the motor coil resistance and can I connect the motor to Home Work Board? I·think that this type of circuit will not give me speed control and direction control. Are there circuits for motors that could give me speed control and direction control?

cyberbiota
08-17-2005, 07:25 AM
Jeffrey-

I'd just measure the coil resistance with a VOM. Do not attempt to directly connect a motor to the stamp. To control speed and direction of the motor you will want to use something like an H-Bridge circuit. You can either roll yer own, or purchase a motor control IC such as the L293-D.

peter

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Peter C. Charles

Director, Research and Technology
CyberBiota, Incorporated
Peter.charles@cyberbiota.com (mailto:Peter.charles@cyberbiota.com)
http://www.cyberbiota.com (http://www.cyberbiota.com)

Chris Savage
08-17-2005, 08:10 AM
Jeffrey,

·· Please start a new thread when asking non-related questions in a thread.· Thanks.

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Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)