Teardown of a DMX controlled UV disco light.04:33

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Published on September 30, 2017

This is one of those mass produced devices that has used some very clever tricks to get big results at very little cost. It’s a 12 LED mini PAR style light with DMX control plus a variety of built in effects with a sound activation option.
The most perplexing thing about this light is the complete lack of current regulating circuitry for the LEDs. Not even a resistor, and seemingly nothing on the PCB getting hot. The power supply is putting out about 10.5V and my best guess is that the circuitry relies on circuit impedance and the increasing LED voltage in relation to the current to add a PWM prescaler to give the equivalent of about 350mA through the LEDs when at full intensity. The power supply is set at around 10.5V to nudge closer to the combined voltage of each circuit of three LEDs.
The control chip may have 16 bit resolution PWM modules in it, which would suit that approach.
I’m going to have to ‘scope these units out to see what sort of waveform is across the LEDs.
Although masquerading as a UV light, this unit uses the classic near-UV LEDs that are well into the blue end of the spectrum and create a strong violet glow that stimulates fluorescent pigments. It’s not true longwave UV, but has a similar effect.

RS485/DMX receiver-transmitter 75176B
Display segment driver 74HC595D shift register
Processor STM8s003f3p6 value 8-bit CPU with internal 16MHz clock.
Power supply switchmode chip DK112

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