Not too long ago, I went to Radio Shack and bought a light to frequency converter. This little chip uses logic and has a max voltage of 6V. You can measure the output frequency of it with a PC or multimeter or anything else. I found that I did ot have anything to do this with, so I wanted to light a LED with it.. The thing with logic output is you get <30mA with it. That won't do jack didley squat without interfacing with it. So what do you do to get the LED to light? In the KHz range of pulses, you won't notice the LED flashing, so I'm not going to tell you. Sound, though, is more practical. The average hearing range for people is 20Hz to 20KHz. So, lets get started with sound output.

The schematics is so simple, you will think " Why didn't I think of that?"

Step 1: Parts You Will Need

1. The radioshack TSL230 Light to Frequency Converter
2. The TLC555 IC
3. Solderless Breadboard
4. Solid core connection wire (for the breadboard)
5. 9V PP3 battery
6. 5V fixed voltage regulator
7. Small Speaker
8. 9V battery clips

Step 2: The Connections

Insert the 555 timer, the light to frequency converter, and the voltage regulator into the breadboard. If I were you, I would put some space between the parts. I'm also assuming you know how to use the breadboard.

Using the wire, make the following connections on the 555 timer: pin 8 to pin 4 to speaker to battery positive supply; pin 6 to pin 2; pin 1 to ground.

Now make the following connections to the light to frequency converter: pin 3 to pin 4; pin4 to ground; pin 1 and/or 2 to pin 5; pin 6 to pin 2 of 555 timer; pin 7 and 8 optional, but if used, connect to pin 5.

Finally, the voltage regulator: Pin 1 to battery positive; Pin 2 to ground; Pin 3 to Pin 5 of light to frequency converter.

Connect the battery clip accordingly to where you chose where the battery positive supply and ground would be.

Step 3: Testing/using

Connect the battery to the battery clip. You should hear a tone through the speaker. To adjust this tone, put more light or shade over the light to frequency converter. The purpose of the 555 timer is to invert the signal from the converter, the reason for sinking is the timer will sink more than it can source and make the speaker usable. To adjust the volume, insert a 100K potentiometer between the speaker and timer.
A video of the product: