Instrument controlled by brightness of light!

Create a functional circuit diagram that makes an instrument controlled by brightness of light!

This is one of the 48 projects for our Instructables: Made In Your Mind (IMIYM)exhibition at the Children’s Museum of Houston showing from May 26, 2012 - November 4, 2012. Produced in partnership with Instructables, IMIYM is an exhibit where families work together to build different fun, toy-like projects that help construct knowledge and skills related to science, technology, engineering, and mathematics while instilling a “do-it-yourself” attitude in kids so they feel empowered to explore, tinker, and try to
make things themselves. To learn more, check out the article here.

For this project, we were inspired by the How to Make an Easy PhototheraminInstructable created by TigrisLi (which, as I discovered is based on the Audible Light Probe by Forrest M. Mims III of Radio Shack books fame) , but there may be others on Instructables that are also similar. Often, the materials and process for building our projects are designed for use with a large number of visitors (we see over 800,000 annually) and the need to ensure safety in a mostly non-facilitated environment (in other words, no soldering). So, yes, many of these projects have room for improvement in both materials and methodology, which is PRECISELY what we want to encourage the kids to do. So please do share your ideas for improvement and
modifications!

Step 1: What You Need

We are selective in our materials for cost, ease of use, and safety due to our high traffic (800,000 visitors annually). So, for our purposes, this design worked best. But you may have other ideas - please share! Most of the electronic components you should be able to get at Radio Shack or similar, but I've listed below where we purchase ours in bulk

• 1 - 2N3904 Transistor (we buy ours from Jameco)
• 1 - 2N3906 Transistor (again, from Jameco)
• 1 - 0.1μf Ceramic Capacitor (once again, Jameco)
• 1 - Photocell (yup - Jameco)
• 1 - 40Ω 0.2W Speaker (this is from All Electronics)
• 2 - CR2032 Coin Battery (from Batteries and Butter)
• 36 inches – Copper tape (you can get this from craft stores that sell stained glass supplies. Since we need so much, we purchased ours throughAmazon)
• 1 – Phototheramin Template (see attached file below - the project can be done without the template, but it helps, especially if you aren't familiar with circuits)
• 1 – 5”x7” Chipboard (cereal box cardboard will work, but we purchase ours in bulk from U-Line)
• 1 – 1” Double-sided foam tape (for most people, just pick up a roll. We purchase individual squares from U-Line to help reduce waste 
• Scissors
• Masking Tape
• Hole Punch

•  Phototheramin Template v3.pdf

Step 2: The Video

We offer optional video segments of each step for this project in the actual exhibit. Here is a compilation of all the steps.

Step 3: Step 1 - Mounting the Template

Cut out the Phototheramin Template. Use masking tape to tape it to the chipboard along three sides, avoiding the side with the boxes. Cut along the line to cut off the boxes from the rest of the template. Use masking tape to tape the remainder of the template to the chipboard. 

Step 4: Step 2 - Adding Battery Flap and Holes

On the piece just cut off, cut along the SOLID line to create two boxes. Use masking tape to tape the paper on the smaller box (the one with the dotted line) along all sides. Tape this box to the top of the gap along near the top right side so that the dotted line is aligned with the solid line to create a flap. Use the hole punch to punch holes in the three circles (photocell and the 2 speaker wires).

Step 5: Step 3 - Laying Down the Path

Place copper tape over all the SOLID black lines. Make sure to ONLY cover the solid lines, not the shapes or dotted lines. Now, place a small piece of masking tape over the rectangle with the dotted lines. Next, place a piece of copper tape over the thick dotted line on the template. Make sure it connects to the solid line at the bottom. On the flap, start a piece of copper tape halfway up the inside, then run it over the top along the dotted line onto the copper tape leading to the top line of copper tape. 

Step 6: Step 4 - Adding the Transistors

Find the 2N3906 transistor (the number is printed on the transistor). Bend the leads and orient it over the image on the template so its flat edge matches the flat edge on the image and the leads are over copper tape. Use small pieces of copper tape to attach it to the copper tape already in place. Repeat with the 2N3904 resistor.

Step 7: Step 5 - Add the Capacitor and Photocell

Use small pieces of copper tape to attach the 0.1 μf capacitor into its place. It doesn’t matter how it is oriented. Place the flat head of the photocell (the area with all the lines on it) through the hole you made and use copper tape to attach the leads. It doesn’t matter how it is oriented. 

Step 8: Step 6 - Add the Speaker

Look on the back of the speaker and find the “+” sign and the wire next to it. Run the wire from the backside of the card through the “+” hole and use copper tape to attach it to the copper tape below the 2N3906 transistor. Make sure the metal on the wire is touching the metal on the copper tape. Run the other speaker wire from the backside of the card through the other hole and use copper tape to attach it to the copper tape along the bottom. Make sure the metal on the wire is touching the metal on the copper tape. Use the double-sided foam tape to attach the metal part of the speaker to the back of the chipboard card.

Step 9: Step 7 - Power!

Stack the two coin batteries on top of each other with the textured bottom of one battery on the “+” smooth side of the other. Place the stack under the flap so both the bottom and the top of the stack are on copper tape. Secure the flap with masking tape. 

Step 10: To Use...

To play your Phototheramin, flip the card over so that you can see the photocell. Move your hand closer and further from it to change the tone you hear. When done, simply remove the batteries from the flap to turn it off.

A fairly simple explanation we use with the kids who visit the Museum is that this is an example of an electrical circuit where electricity flows from the batteries, through the circuit, and back to the batteries. The speaker plays a tone created by the transistors and capacitor. This tone is controlled by the photocell, which acts as a sensor. The more light the photocell receives, the higher the tone and the less light, the lower the tone. This is also a great project to discuss how some electrical components (like transistors) can control how the electricity flows through a circuit, how some (capacitors) store up electrical energy and release it, and how some circuits have control mechanisms - sensors (in this case the photocell) that controls how the circuit acts.