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ULN2803A for external LED - question

Posted by Arshish Maneckji on June 9, 2014 at 9:19pm

Hi,

Have bought a ULN2803A darlington array and am using it for external LED's.

They work fine but they are always on. Is there a way to have  TX switch controll all LEDs such that I can switch them off during the day.

I fiddled around with pin A9 for camera shutter and got that to work on a camera shutter switch set as relay but since its a shutter functionality, it comes on and switches off after some milliseconds. Also with the camera shutter approach I lose all indications I would get if connected to the NAV lights pins.

I am contemplating putting a manual switch on the quad on the +ve wiring for all leds.

Is that the  only way?

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Replies

  • Arshish Maneckji June 10, 2014 at 5:51am

    No replies.....?

    • Brian Sigmon > Arshish Maneckji June 10, 2014 at 4:42pm

      Hi - I had my APM setup to do what you are describing.  I could flip a switch to either turn on or off a sting of LEDs using the ULN2008 driver.  I had an output tied to relay using channel 7 through the APM.  My setup was either on or off  - no type of timer was involved.

      I don't have this setup right now as I reconfigured my copter.  

      I hope this helps.

      • Arshish Maneckji > Brian Sigmon June 11, 2014 at 1:58am

        Thanks this is helpful however I have different LED's wired to the ULN2803 at different pins. I have wired them as shown here: http://copter.ardupilot.com/wp-content/uploads/sites/2/2012/12/leds...

        Some Questions:

        1. How would the approach you have outlined switch off ALL LED's?

        2. How would I ensure the buzzer is not switched off.

        • Brian Sigmon > Arshish Maneckji June 11, 2014 at 5:05am

          I suppose a quick  way to accomplish what you are describing would be to simply add a relay to the positive lead of the circuit (based on the diagram link).  Ensure that the buzzer positive terminal bypasses the relay.  Relay could be driven by the APM as we have discussed or via a radio channel switch product.

          If you don't care to control this via the radio - simply add a switch in the same position as you have already proposed.

          I can think of other methods but this would be the fastest to implement.

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