Off Topic : Reverse engineering Smart Superflash 317R rear light

A project log for Ultra low power LED

<1.5µA current consumption when continuously on, optional flashing mode

Christoph TackChristoph Tack 04/04/2020 at 15:400 Comments

This project log is a bit of a diversion.  I had to repair this bike light, because the momentary switch started failing again.

Very bright and sturdy bike light, unfortunately protection to water ingress is not great.  The contacts on the push button start to corrode, which makes it hard to turn the light on or off.  Replacing the switch only temporarily solves the problem.

There are two red 5mm LEDs inside and a red SMD3535 LED.  The Lumileds L135-A589003500000 might be a good replacement for the original 0.5W LED.

Quickly drawn schematic

The controller is fed through an RC-filter, probably to prevent it from resetting when enabling the 3535 LED when the batteries are running out.

The 360K resistor determines the clock frequency of the controller.  Pin 6, 7 and 8 control the LEDs.  If you used a standard MCU, you would put a series resistor in any of these lines.

Blue : 3535 LED cathode, green : 5mm LED cathode

The controller works in a six burst mode.  During the first four bursts, only the 5mm LEDs are on, followed by two bursts where only the 3535 LED is on.  A 6-burst cycle takes 745ms.

The 3535 LED burst is 30ms long.

Zooming in on the bursts on the cathode of the 3535 LED (blue trace).

125ms from the start of one burst to the start of the next one.

A burst on the 5mm LEDs consists of 5 pulses

The two 5mm LEDs are on simultaneously.  One pulse is 750µs ON, followed by 2.28ms OFF.