mesuring vibrational frequency with light

[bridgeto67]

Dear Science Buddies,

I recently took up the project of measuring vibrational frequency using light for my science fair. I had purchased all the materials to make the light-to-voltage converter.

My parents and I set up the light-to-voltage converter circuit and connected it to the 5 volt battery source. We checked all of the connections and they were all set up correctly as in the diagram. When we connected the supply, it burnt out the light diode. There was an electrical smell and the diode turned brown.

Our question is: Why did this happen? What could have gone wrong? We checked the circuit diagram several times to make sure we'd connected pin 1 to the black ground wire, pin 2 to the supply (red) wire, and pin 3 to the resistor. We used a digital multimeter to measure the power source, and it was only 5V (3-AA batteries). The max voltage for the converter is 6 V.

We are going to order more of light diodes for the experiment, but we're wondering what went wrong with the circuit so we can fix it.

Also, do we need a solderless breadboard to make this circuit? We didn't use the breadboard, and I don't see why we need it. We connected the supply and ground wires directly to the photodiode sensor. In order to connect the wires to the photodiode sensor, we bent back the pins on the sensor so that the wires wouldn't fall off. Could that be why the photodiode burnt out?

Thanks in advance for an help you can offer,
Mike Flisk (grade 7)

[kgudger]

Hello and welcome to the forums!

The most likely thing that went wrong is that the light to voltage converter is connected wrong. Did you get a data sheet with the converter, or can you download one from the distributor that you purchased it from? While the picture in the experiment's procedure is probably correct, it is always best to make sure that the part you purchased looks like and is hooked up like the diagram. Sometimes they use different packaging and change the connections.

Second, I would try running this experiment with only 2 batteries instead of 3 at first. This means you have a little less voltage and can do less damage if something is wrong.

Lastly, put the voltmeter on the "current" (or amps) setting and put it in series with the power supply (batteries). If you hook up the circuit and there is lots of current (read the data sheet to see what is reasonable) then immediately disconnect the battery and check the circuit again.

The experiment says you don't need the solderless breadboard, so you should be fine as long as you hook it up correctly!

Good luck!
Keith