designing circuit for led status

[riksworld]

Hi All,

I have been looking around for a Led status schematic which include a green and red leds for the status of some of my aquarium.

for an example, when a pump is off, the led would be Red, when the pump is on, it would be green, the pump runs on 12 volts so the power to the green led is not really a problem, but how would I drive the Red led as there would be no power, I am assuming I need a secondary power supply to drive this other Led and a transistor?

Can anyone on here please off there advise on this?

thanks to all who replys.

 

[BradtheRad]

Install the red led across the switch that controls the pump.

It will permit a small amount of current will go through the pump. If this is not allowed then disregard my suggestion.

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[crutschow]

Isn't the absence of a green light sufficient to tell you the pump is off?

If not then you will need a add a battery to power the red light, if no other power is available. How often and how low do you expect the red light to be on?

 

[riksworld]

Thanks for the replys.

The green led will be lit all the time exept when the pump is on, then it will go to red, the pump will be on every other day for around 10mins

 

[BradtheRad]

Here is a method using a single transistor, in case you do not want any current going through the pump when it is switched Off.



If the green led lights dimly when it should be off, add additional diodes inline.

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Switch the green and red if necessary.

 

[riksworld]

Can you recomend a suitable transistor?

 

[BradtheRad]

Can you recomend a suitable transistor?

A general purpose low power NPN will do the job.

Popular types are 2N3904, 2N2222, BC548.

It does not need to carry much power. It does not need high gain.