This is a replacement PCB for a cycling helmet light made by ABUS. It can be equipped with a LiPo cell and replace the original "ACHV" PCB.

Unfortunately the original light is powered by a single CR2032 coin cell, which not only limits its runtime severely, but also is not rechargeable. This itself is just how ABUS makes products, but what really dumbfounded me were the misaligned LEDs. They just light straight into the rubber part of the light and only some scattered light can be seen from outside. Interestingly enough, the light made it to version 6 as the photo below shows "ACHV_V06".

The LiPo is fully protected: over- and undervoltage, temperature limit and short circuit.

The connector itself is a 90° micro USB which snugs in perfectly next to the battery and rubber protector. A great amount of measuring went into the correct positioning of the 6 red LEDs behind the plastic reflector. This worked out surprisingly well as the can be individually seen in the top photo. There are two more LEDs on the PCB, they are charging indicators and are directly switched by the TP4056.

There are 4 different modes which are cycled through by pressing the button:

• 1: 100% on (ON)
• 2: 50% on, 500ms period (Blinking)
• 3: 20% on, 300ms period (Slow blinking)
• 4: 3% on, 1000ms period (Energy saver)

The battery used is a 3.7V 120mAh LiPo which drives the 6 LEDs at ~10mA each, the ATTiny draws 0.2mA while running. This means that in mode 1 it can do roughly 2h on a single charge. In mode 4, this runtime goes up to 65h, since it is only pulsing the LEDs.

Standby time can be calculated with the deep sleep current of the ATTiny of <0.1µA. This would result in 1.5 million hours standy time.. More realistically the rest of the circuit uses more current and limits this time, so a couple of weeks top.

Please note that there is no battery included by default, due to not being able to ship LiPos affordably. You buy the PCB, solder on a battery and pop it into the original AVHV2 rubber and plastic frontplate. I can send you a link for a cheap battery if needed, but any Liion cell with the right dimensions and voltage should work. The rubber and red frontplate are obviously also not included, you're buying only the PCB as pictured.

There is an alternative version for an ABUS ACE helmet here: https://www.tindie.com/products/petl/rechargeable-led-bicycle-helmet-light-acy/