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16  Forum 2005-2010 (read only) / Frequently-Asked Questions / Help designing a simple circuit?(Transistor/Relay) on: September 12, 2008, 09:37:16 am
Good morning,

I'm hoping this isn't too much to ask but I'm doing a little Arduino with Ruby demo at a future Ruby Users Group meeting and would like to have a neat project setup.

So I'm going to build a simple Barmonkey (to be called Barduino).  The idea being, two available windshield washer pumps, controlled by the Arduino to dispense drinks.  Here's what I'm looking at...

I'll be using two 12V 1A water pumps and here's what I think the circuit should look like but I'm still somewhat new to electronics...

Arduino digital pin -> resistor -> transistor (transistor goes to ground and to a relay).  The relay will connect to the 5v out on the Arduino as well as the 12V 1A DC power supply (which I think I'll be using a wallwort for).  And the output of the relay will go to the pump which will be using the Arduino's ground.

There will also be a diode in there to prevent the 12V 1A from going back to the Arduino....

So in theory...

Turn on the digital pin which triggers the transistor to send power to the relay which will then open the 12V to the pump which is grounded in which case will then turn on.  Once the digital pin is turned off, everything will stop.

Does this sound right?  And this would be done twice, one setup for each pump.  So only 2 digital pins will be occupied.

On the Arduino software side I'll simply be sending serial commands to turn the pins on and off.

How feasible does my circuit sound?  The only thing I'm unsure of and I'll know a little bit later when I scout the local electronics warehouse is the transistor type and relay I'll need.

I can use a lower power transistor that the Arduino is capable of triggering, correct?  And then the relay will need to be capable of 12V 1A?

Any responses will be greatly appreciated. Thanks smiley
17  Forum 2005-2010 (read only) / Frequently-Asked Questions / Good place online to buy components? on: December 12, 2006, 10:10:15 am
I was curious where everyone shops online to get components and sensors?  The shop has some but there are some basic components I need that Radio Shack doesn't have and are impossible to find at my local electronics surplus store.  I'm also looking to buy a bunch LEDs just to have on hand for this or that.

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