Digital output on Maestro

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1

Hi,

I’m trying to use a digital output from a Maestro to power an array of LED lights. The lights use 14v, so I am using a relay to switch the higher voltage circuit.

The relay needs 3v minimum to switch, and when active it draws about 70mA. When the digital output channel is turned on, the voltage across the signal and ground pins is just under 5v, which would be fine to switch the relay, but when I connect the relay, this drops to 0.6v, which isn’t enough to trigger the relay.

I thought that maybe the power required was too great for the USB power supply alone, so I connected the Vin pin on the board to a regulated 6v supply. This did not improve the situation.

Is there something I’m missing here? Or is it simply not possible to power a relay from the maestro? Is the current demand too high for the signal line? If I can’t use a relay, are there any better ways of achieving the same thing?

Any advice or suggestions would be much appreciated!

Cheers,

Greg

2

Hello,

The output current on the Maestro is limited to about 25mA, so yes - it is not going to be strong enough to drive a 70mA relay. There are other reasons you would not want to directly connect a microcontroller output to a relay (voltage spikes), so you should probably google for “relay driver circuit” or something to find a better way to do it.

In general, the easiest way to control a simple 14 VDC load is to use a low-side, N-channel MOSFET. We build such a MOSFET in to our R/C switches, so you could just use one of those if you do not want to have to do much circuitry yourself. Note that with a MOSFET circuit the Maestro cannot be electrically isolated from the load - they must share the same ground.

-Paul

3

Thanks for your advice Paul,

I will have a look into those options and see what I can come up with!

Cheers,

Greg