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Topic: PWM 12V pump control (Read 1 time) previous topic - next topic

mlerner

Howdy,

So i'm building a simple circuit using arduino's PWM and a potentiometer to control a 12V pump(powered by an external source). I tested the circuit with an LED and it worked just fine. I connected the circuit to a uln2803 darlington transistor pair and again tested the circuit with an LED powered by an external source through a darlington pair. The LED lit up but I could not control its brightness. The LED is connected to the output of the IC and the + of a 5V source. A simple diagram is shown below.


Any idea's as to why it's not working?

Thanks

kerimil

#1
Aug 16, 2012, 04:24 pm Last Edit: Aug 16, 2012, 04:26 pm by kerimil Reason: 1
what about ground ? both the microcontroller (arduino) and external power has to have common ground

your diagram shows that only external power is connected to the ground pin on the ULN... what about arduino ?

mlerner

Currently, the source and the arduino do not share a common ground.

CrossRoads

"the source and the arduino do not share a common ground"
That would be a problem. As far as the ULN2803 is concerned the base voltage is just floating.
Need the grounds connected so all signal levels are properly referenced to something.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

kerimil

there is your problem

look

both arduino and power source ' - ' have to be connected to gnd pin on the ULN chip

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