For this project, we are creating a guitar strap with a built-in effect pedal. We will first build out our pedal from scratch using a DIY kit available from (https://www.modkitsdiy.com/), then modify the design to include an FSR (force-sensitive resistor) sensor that will allow the user to apply the effect to their guitar sound using pressure between the strap and their shoulder.

Supplies

Thunderdrive DIY Guitar Pedal (https://www.modkitsdiy.com/pedal/thunderdrive)

Force Sensitive Resistor (Amazon)

40/60 Electronic Solder + Iron

Any Guitar Strap

Stranded Wire

Foam

Scrap Fabric

Step 1: Test FSR With Small LED Circuit (Optional)

If you have a breadboard, LED, and power source, it's a good idea to test your sensor to see if it's working properly!

On the breadboard, connect the LED positive side in parallel with any simple resistor and the ground side to your power source. Then attach your FSR to the circuit with one side to power and the other to the resistor (doesn't matter which side). In this case, I am using electric tape to connect wires to my breadboard and the 5V power on an Arduino.

If done properly, you should see the LED glow brighter depending on how hard you press the FSR!

Step 2: Assemble the Effect Pedal

For this step, please refer to the instructions that were included with the DIY guitar pedal. The Thunderdrive Pedal instructions can be found here

Solder all connections until you get to the 6-point DPDT Foot Switch.

Referring to Drawing 4, the switch is connected to the input and output jacks, and the distortion and output potentiometers. The output is connected to the 4th terminal and controls the gain of the signal passed through the pedal, and the distortion is connected to the 1st terminal and controls how much of the effect is added to the signal as it is passed through.

For this project, we will be inserting the FSR to the distortion potentiometer to allow the sensor to control how much of the distorted signal will pass through to the guitar's output.

Before soldering these joints, refer to the instructions to test the pedal with a multimeter. Also, check if you are able to get a signal through the pedal when your guitar is plugged into it.

Using alligator clips, attach the FSR between the 1st terminal of the switch and the connection to the distortion potentiometer. Then test the signal while pressing the sensor to receive a distorted signal.

If all tests well, move on to the next step.

Step 3: Connect Strap-Length Wires to Pedal

Arrange the strap, pedal, and sensor flat on the table. Identify where on your strap that the sensor would be best placed on your shoulder. Then measure and cut two wires to connect between the sensor and the pedal on the strap. (Mine measured out to be about 17in each). Strip wire and twist strands together.

Attach one wire to the 1st terminal of the switch. Attach the other wire to the wire connected to the distortion potentiometer. Twist the wires together to form a joint, then solder those connections.

Step 4: Create Foam-Casing for the Sensor

Cut out a square piece of foam the size of the FSR. (About 1.5in x 1.5in)

Using a knife, carefully slice the foam in half to reduce thickness.

Place the sensor between the two halves and tape together using electric tape.

** it's useful to mark the top side with another piece of tape!

Step 5: Sew a Pocket for the Sensor

Cut a piece of any fabric to about 4.5in x 3.5in.

Fold in half and sew the sides to create a small pocket for the FSR.

Attach pocket to the strap at the place you marked. I opted to wrap a piece of electric tape around my strap and hot glue the pocket in order to prevent my strap from being damaged unnecessarily.

Step 6: Solder Connections to the Sensor

Solder the wires from the pedal to the FSR.

**the terminals for the sensor are quite small, so it's a good idea to tape down the wires and sensor to make it easier to solder the joints together

Step 7: Testing the Circuit

Your product so far should look like the first picture. Remember to add a 9V battery to your pedal.

Using 1/4" cords, connect the input of the pedal to your guitar and the output to a source like an amp or a speaker. Try strumming the guitar to see if a signal comes through, then try adding force to the sensor to add distortion!

Finally, attach the circuit to the guitar strap. For the pedal, I used a stretchy velcro strap to secure it, and taped the wires to the guitar strap to ensure they don't move while wearing.