A friend of mine would like to convert her bottle dynamo (bike generator) to run a LED light. The light needs to stay on for maybe 90 secs when the bike is stopped, and needs to blink (using a particular pattern).
The generator is labelled as 6V, though it has been difficult to establish what that actually means in practice: the available information suggests that peak voltage varies with speed (see here). On the assumption that the "dynamo" is producing higher voltage than is needed by the uC, Here is what I have in mind for the solution:
The idea for two capacitors as following:
- it is difficult to find an affordable supercap that is rated for high voltage, while 5.5 V 1F caps are cheaply available
- C1 smooths out the input to the Vreg
- C2 is what the LED/uC runs on while stopped. The LED might not be as bright (controlled by R1), but at least it is on.
I am concerned about what happens when the voltage generated by the "dynamo" is not sufficient to supply the uC power, and about wasting power in the regulator. Do you have suggestions for mitigating these problems, and is there anything else I am missing?