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Forrest M. Mims III: Toy Organ Kit

DIY 555 Timer Circuit Music Maker

By Forrest M. Mims III

Description: Toy Organ Kit
Assembly Time: 1 hour
Skill Level: Beginner

Technology keeps everyone in the game

The Toy Organ Kit is a music maker based on a simple 555 timer circuit. With the addition of a resistor, some capacitors and some push buttons switches, you can generate several different tones. With the addition of a couple potentiometers, you can control the volume and the pitch of the note. Even more, when you press several buttons at the same time, another unique tone is generated.

 555 Timer & Socket 1) 555 Timer & Socket

U1. When installing ICs, it is good practice to use a socket. If the IC were to fail, it can be easily removed and replaced. Notice there is a notch on one end of the socket. Be sure the notch on the socket matches the notch printed on the PCB. The 555 timer also has a notch at one end. Install it the same way you installed the socket.

2) Capacitors

C1 – C8 are not polarized so they can be installed in either direction. You can install the capacitors in different positions on the board. Since each value will create a different tone, you may choose to install them ranking from high to low or low to high. You can also use other value capacitors to make different tones.

Capacitor Codes
C9 is polarized so watch the polarity! There is a stripe going down the side of the capacitor indicating the negative lead. The negative lead goes in the round pad while the positive lead of the capacitor goes through the square pad of C9 on the PCB.

3) Resistors

R1 (100K) and R3 (1K) are potentiometers and will be installed in the enclosure. You will need to make wire connections between the pads on the PCB to the terminals on the potentiometer.

Connecting Wires R1 - Bridge pins 2 and 3 together with a small piece of wire. Connect a wire from pin 2 or 3 of R1 to the pad closest to the battery location on the R1 location. Connect a wire from pin 1 of R1 to the other pad on the PCB; this pad is closest to R2.

R3 - Connect a lead from pin 1 of the 1K pot to the pad on R3 closest to the "Toy Organ" label. Connect another wire from pin 2 of the pot to the remaining pad for R3.

R2 is a 10K resistor and can be installed in either direction. (Brown – Black – Orange)

4) Switches

S1 – S8 will also be mounted in the enclosure in whatever position you choose. You will need to make wire connections from the PCB to the solder tabs on the switch. The switches are installed from the outside of the enclosure, so you will have to solder lead wires to the switch before installing it in the enclosure. The alternative is to solder lead wires to the PCB, then install the switches in the enclosure and complete the wire connections to the switches.

5) Speaker

The speaker will also be mounted in the enclosure wherever you choose. Connect a wire from the right side terminal (R) of the speaker to the square pad for SPKR. Connect a wire from the other speaker terminal (L) to the round pad. (Figure 4.)

6) Battery Snap

Connect the red wire from the battery snap to the positive (+) pad on the PCB labeled BT1. Connect the black wire to the negative (-) pad.

7) Enclosure

Connecting Wires This portion of the project requires your own creativity. Use white masking tape over the lid of the enclosure so you can pencil in where you would like to mount the switches, speaker, and potentiometers.

You will drill 0.5" holes for the switches and 5/16" holes for the pots. You should also drill a shallow (not all the way through) 1/8" hole for the tab that keeps the pot from free-spinning when installed. Drill 1/8" holes for mounting the speaker. You may want to set the speaker on the lid and run the pencil inside the mounting circles to mark where to drill. It is also a good idea to drill a few holes to let the audio from the speaker out of the enclosure.

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