PROJECT PLEASE HELP

[mark_jarman1]

I am currently at college and i need to do a electronic project for AS level.

I was thinking of a wind up torch

Can anyone help me with ideas of how to make one?

cheers

mark

 

[charcoal]

The most difficult part of making a wind up device is the storage of energy between the crank handle and the circuit itself. the best ways I can think of for this are: clockwork motor and dynamo combination (if you can find somewhere that sells spring driven clockwork motors), rechargeable batteries floated across a dynamo attached straight to the handle, or a capacitor based method.

I’ll go over them in that order.

The most difficult bit of a clockwork design is getting the motor and also finding some way of attaching it to the dynamo. Motors taken from old clocks are useless unless you can make a way for the output to drive a dynamo at a decent speed (which requires serious gearing) and fast clockwork motors such as the type you get in wind-up radios and old gramophones are expensive, usually custom made affairs. they are also usually far too bulky to put even a medium sized torch. the alarm gearing in small 1950s alarm clocks may be suitable but I have no idea how to get one of these out of the rest of the clock body. most of the obstacles here are mechanical, not electronic.

With a rechargeable battery all you need is to hook the battery up to the dynamo in a charging config (pos to pos, neg to neg) and have a diode and some form of current limiter to prevent damage to the battery. then the output from the battery is connected in the normal way to your light source. the only problem with this is you need a battery suitable for variable power and infrequent recharging.

In order for a capacitor bank to run a light source for any reasonable length of time you’d need to use high capacitance devices like memory retention capacitors. these work at about 5.5v and can’t supply a large current for very long. if you used a low current light source (I’d recommend using one or more high brightness blue leds) and some form of current limitation then this may be a workable option.

Overall the best method to choose depends on how good you are with mechanical devices (I’m pretty much useless at working with small mechanical stuff like gearing) and what sort of light source you want to use. (caps like those above won’t power a light bulb, but then again I wouldn’t recommend using a bulb in a wind up project)
I’d probably go for the floating battery method and high brightness leds with voltage/current limiter.

Anyone else think of anything I missed here?

Good luck with your project.