Alternating Voltage reader

I am doing a school project where we are build a linear dynamo as seen here http://www.sciencespace.nl/servlet/supportBinaryFiles?referenceId=42&supportId=4320 that needs to be shaken by children in order to create power.

What we are building is based on the Mechanically powered flashlight - Wikipedia
The idea is that with the help of Arduino I can read the voltage and that at a certain voltage leds will go on. For example at 0.2 voltage red led will turn on, at 0.4 voltage orange and at 0.7 the green led.

From my snooping around on the internet it looks like Analog to Digital Conversion (ADC) is the only option that seems viable (If there is a beter option please post this).
But i am a novice and I have no idea how to build this can anyone help me with this?

PS. At the moment we are not storing the power anywhere but I do take that this is a requirement for what I am trying to do?

I think I would use a bridge rectifier to turn the AC pulses into pulsed DC, then store the DC in a fairly large capacitor with a resistor across it. The resistor will slowly drain the capacitor so the charge (voltage) in the capacitor is a measure of how fast you are pumping energy into it.

Just connect the minus (-) side of the capacitor to Arduino Ground and the plus (+) side to one of the analog input pins. That lets you read the voltage and then it's just software to light the appropriate lights.

Thank you John for replying to my topic I have question regarding the bridge rectifier.
So far the highest voltage we measured while using our own linear dynamo was 0.7 (This was when we shook it really hard) but from my understanding a diode creates a drop in voltage around 0.7 Volt . So with that in mind is it correct that this solution wont work? The linear dynamo will need to generate a higher voltage I take it?

And can I just interface our linear dynamo through a copperwire to the Arduino?

...but from my understanding a diode creates a drop in voltage around 0.7 Volt.

That is correct. For detecting and "measuring" line-level audio signals (around 1V), I use a [u]peak detetcor circuit[/u]. (This circuit, "throws-away" the negative half-cycle.)

And can I just interface our linear dynamo through a copperwire to the Arduino?

Not a good idea. The Arduno can be damaged by feeding-in negative voltages (the negative half on an AC signal).

There are a couple of simpler solutions. You can use a series resistor and a diode wired "backwards" to ground to "short-out" the negative half cycle.* Or, use a pair of diodes ([u]like this[/u]) to protect against negative voltages and voltages greater than +5V.

Another solution is to bias the Arduino input at 2.5V with a pair of equal-value resistors, and a series capacitor to isolate the DC from your generator. You can then compensate for the bias in software.

If you use the peak detector or diode protection method, you can use the 1.1V ADC option and get 1mV resolution.

  • The protection diodes won't conduct until you hit about +5.7V and -0.7V, but that is still safe.

Thanks for responding DVDdoug il have to take a look at these methods to see which is best and easiest to do for me like I said i am a novice at this stuff.
Also I am correct that John solution wont work then if the dynamo only creates up to 0.7 volt because this question was not anwsered?

And can I just interface our linear dynamo through a copperwire to the Arduino?

Not a good idea. The Arduino can be damaged by feeding-in negative voltages (the negative half on an AC signal).

I might have formulated this sentence wrong what I meant is how would I connect/interface my linear dynamo to my breadboard because I have no idea what is safe and what will work.
http://www.sciencespace.nl/servlet/supportBinaryFiles?referenceId=42&supportId=4320 our dynamo looks exacly like this its a PVC pipe with a coil of copper wire (except with out the led) And I have never heard of the term series capacitor what does this mean?

You can use Germanium diodes 0.25 to 0.3 V or Schottky Diodes 0.3 to 0.8 V
or you can have more turn in your coil to get higher output voltage.