Hack a momentary on-off button 

I have several very bright UV LEDs that I bought for cheap online that are built into nice housings of UV curing lamps and flashlights that can already be automatically powered by a USB attachment and can run all night off a simple battery pack. 


One problem is that I want to control them with a relay, which lights turned on whenever they received USB power. But instead, they need to be attached to USB power and then clicked on via usb. The button can't just permanently held down and then plugged into USB power either.


So if I want to use them and control them with my relay, I need to find a way to hack the control going to little circuit board in the simplest way.  


Figured maybe some of you all had experience with this exact problem. 


Board of light

Also, I cannot just add like an extra wire that would give a little blip turn the button on or off. I change to the circuit board that would permanently put it in a state where if it's receiving power the light turns on. 

Because basically we are attaching these lights to a distant black box that is either on or off, and nothing dynamic

Hi Andrew,

If I understand you correctly, you want to turn on the LEDs when USB power is applied.  The easiest way I can see to do this is to reroute the red wire to USBC VBUS, via an appropriate current limiting resistor.  This bypasses all the electronics in your photo.

You could insert the current limiting resistor in the USB cable for better heat dissipation, or use a DC-DC constant current source instead of a resistor if power consumption is a concern.

Further to @htarold 's excellent suggestion, you can replace that entire PCB with a simple USB breakout board (e.g. USB micro attached below) by removing the red wire and attaching it to VCC on the breakout board, and removing and attaching the black wire to GND.