When I started thinking about energy harvesting, and read about the kit, I had a very clear idea in mind what to make with energy harvesting. In the Netherlands, where I live, a lot of people ride bicycles. There's even a Wikipedia page about it! As you can read about it, there are more cycles than people in the Netherlands. However, "with great cycling power comes great cycling responsibility". The Dutch law tells that you should have a workign head and tail light on your bike. Regularly, police checks the cycling lanes for those driving without light, and the fine you get for this is 50 Euros. Bad.
Until a few years everyone had a 'dynamo/alternator' on his / her bike, a small device that is clamped to the wheel when light is needed, and transforms mechanical energy (rotation of wheel) in electrical energy. At an appalling efficiency of 12% for regular alternators, and 50% for those in the wheel hub, with 6W of incandescent lighting at the output. Add to that the mechanical noise, unreliable wiring an people generally not understanding electricity, and you get a system that's got a lot against it. A few years ago the use of LED lights on bikes was allowed officially. Now, a lot of people but small LED bike lights:
These are small, easy to use and use batteries. And to be honest: a lot of people loose them, throw them away when batteries are empty, or forget to replace the batteries. In comes the police - > another 50 Euros gone. Bad.
Energy harvesting - Bike light on piezo? No.
Now I thought that the energy harvesting challenge would be a nice way to address this problem; make a solution that transforms energy from cycling into light. Starting at the back light, which is only used to let other people seeing you in the dark, a few red LEDs would be doable easibly, right?
Before I received the energy harvesting kit, I had hoped to be able to use the piezo vibration to just use uneven roads and other vibration to generate enough energy. Unfortunately, piezo was not the solution. First, no piezo was included. Second: a small energy harvesting piezo already costs more than the fine you'd get from the police. Third: the amount of power I need greatly surpasses the amount of energy that's available from piezo harvesting. If you take a look at this slide from the presentation of Linear, you'll see that 30cm2 of piezo would give me 500μW. I need about 100 times more: 2V, 20mA -> 40mW. No go.
But wait; electromagnetic might yield > 10mW!
Energy harvesting - Bike light on Electromagnetic? Maybe.
So I set my thoughts on harvesting electromechancial energy; of course, the good old alternator gives energy, but also a lot of hassle with wires, and it really takes a lot of effort in cycling. I then thought of two solutions
'The regular solution'
The first is the regular solution. You'll understand when you'll read the other option. I thought about how to use non-used energy in the bike to generate electricity. I still wanted to use the vibration of the bike to power the light. I thought about using some linear moving magnet inside a coil, suspending the magnet with two springs. Then I thought about using a speaker to work as generator. I'll have to use one of the Wurth transformers to generate a voltage high enough to get some energy. I did some preliminary testing, and found that it's quite hard to get continuous energy from this setup, and not energy in excess to store energy a long time.
I'll spend another article on possibilities I found that are useful in the future, but not feasible within this project to realize a good energy harvesting setup.
'The weird solution'
One of the things I'd like to do with the energy harvesting challenge is to use the microcontroller. Something I'd really like to make is something that looks like the Revo:
This is a 'persistence of vision' trick with several LEDs in the wheel. It now uses batteries, but maybe an 'energy harvested' solution is also possible. Not within the budget of 50 Euros, but hey, that's also not the price of the Revo. Why call it the 'weird' solution? Because I thought about using a propeller and a small DC motor to generate LED voltage at every spoke, and read out a gyroscope to get the timing for switching on / off each LED. Feasible? Not really, but it's a fun thought.
The 'Energy Harvesting Gadget', aka 'The Ehgg'
Now for the realistic approach. This is something completely different, but a more feasible idea. How about making an egg timer in the form of a fake egg, using a peltier element to generate energy from the temperature difference between inner and outer temperature. Of course, the longer the egg is in the hot water, the less temperature difference you get. The cool part of this solution is that with a temperature sensor you could measure how much heat is going into the egg. The EFM32 could measure the temperature, and integrate the temperature to determine what the state of the egg is: soft, medium or hard. Now just find a way to communicate the state of the egg to the end user. Maybe use a vibration motor?
Conclusion, what I'm going to do next
A last word: why not use solar power for bike lights? You'll need them most in the winter, and most people store their bike indoors....
In the next weeks I'll try to make some proof of concept designs to see what is feasible. I'd really like to do something with bike lights, but I'm afraid I won't have time to finish that in time.The Ehgg is an bit more sure, and very fun, so it's a good fallback design!
