High beam flash for a dynamo light

[steveo_mcg]

I've been thinking about this over the last few days and thought I'd invite some opinion....

One thing I miss on bike lights is a short momentary flash of the "on you go" or "over here" variety. I thought about a couple of fairly big super-caps in parallel to the lights to let them charge with out effecting the lights but with a monetary switch discharging through through a low value high wattage resistor to lighting circuit giving a flash of instant brighter light. Its probably something I'll never do due to the size and dubious value but.

 

[Steve K]

I will steer left and right quickly just to get someone's attention. Or just aim the headlight at the person I'm trying to get the attention of. A momentary high beam would be handy.... but the implementation in a dynamo headlight would be a bit complicated for me.

My light is homemade, and switches between 2 and 4 Cree XR-E's, depending on the bike's speed. If I were in the mood to complicate the circuit, I suppose I could add a circuit that forced a fast, cyclic switch between 2 and 4 LEDs when commanded by a switch. Actually, I've got some unintended flicker of this sort already, although it only happens right around 15mph. I guess I just need to modify my speed to make use of this "feature"! :)
I just wish I knew why the "feature" existed.... very annoying!

Steve K.

 

[pushy]

Justa thought, can't detail the electronics or how to adapt, but in general if its just a flash of a fracrion of a second then how about cannabelizing an old disposable camera that has a flash and connecting it to the dynamo for power. You'd have the electronics already for storace of charge and the switch from the camera?

 

[jdp298]

It would work. Probaly easier to have a supercap and an extra LED somewhere at the front otherwise unused, activated by a non-toggling push switch.

 

[minisystem]

When I was hunting around for LED drivers I discovered a whole family of drivers that exist for driving the flashes of digital cameras and cell phone camera. These, depending on the configuration, use a super capacitor or a charge pump to provide high current flash pulses to LEDs. Invariably, they come in tiny surface mount packages, but tend to have few external components. Here are a couple I looked into:

http://www.linear.com/product/LTC3216
http://www.onsemi.com/pub_link/Collateral/CAT3224-D.PDF

There might be a simple way (ie. without a µC) to rig these up so that a switch would trigger them to produce the flash.