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Indicator LED placement

pizoman

Mar 10, 2012
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I'm trying to figure out where I can place indicator LED's on my circuit for a simple motor controlling circuit using the arduino. I'm using a TIP120 transistor. I want to place a LED to indicate the circuit is on and one that indicates off where the motor isn't moving. To my understanding, the TIP120 transistor connects the collector to emitter when the arduino sends a "high" signal via the base. So when the collector is connected to the emitter, the "on" status led will light up whereas the "off" status led will not light up.

If I placed an led in parallel to resistor R5 when the arduino sends a low signal to the base, will the voltage travel from base to emitter and so the motor won't turn on indicating that the circuit is in an "off" state thereby the "off" status led lights up and the "on" status led does not light up. I've attached a diagram of what I'm trying to do. Sorry if my wording is confusing, it's getting late here on my end.
 

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Arouse1973

Adam
Dec 18, 2013
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Try this it might work. Oh your top LED and resistor is shorted.
Thanks
Adam
 

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pizoman

Mar 10, 2012
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Arouse1973, can you explain how your circuit works? With the way you connected the motor, straight to ground, wouldn't the motor just turn on the entire time?
 
Last edited:

davenn

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Sep 5, 2009
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V1 is the power supply NOT the motor

L1 M is the motor

Dave
 

pizoman

Mar 10, 2012
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Thank you, it works. However, the "ON" led (D2) fades out when the motor turns off. Is this due to residual voltage that's still flowing in the circuit immediately after a LOW signal is sent to the base of the transistor? Is there any way to get D2 to not fade out?
 
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