Introduction: Schmitt Trigger Synthesizer
A Simple Synthesizer using a Schmitt trigger
For this circuit, you may need to connect the audio jack to a guitar amp. A regular stereo out may not have enough gain to hear the signal.
A Schmitt trigger is a type of threshold circuit with positive feedback. The circuit is named "trigger" because the output retains its value until the input changes sufficiently to trigger a change. A Schmitt trigger is a bistable multivibrator; in its inverting configuration it can be used as an oscillator. The integrated circuit chip we are using is called a hex Schmitt trigger because it has six inverters on one chip. For this exercise, you can use 74C14 or CD40106, they are both Hex Schmitt Triggers.
Single inverter
- pin 14 goes to voltage source
- pin 7 goes to ground
- R1 = 10k (resistor between pin 1 and pin 2)
- C1 = .1uF (capacitor between pin 1 and ground)
- The hot tip of the audio jack connects to pin 2, which is the OUTput signal
- The sleeve of the audio jack connects to ground
Step 1: Set Up One Oscillator, and Connect It So We Can Hear It
Step 2: Replace the Resistor With a Photoresistor
Step 3: Replace the Resistor With a Potentiometer
Step 4: Multimeter: Measure the Resistance of the Photoresistor and Potentiometer
Write down the range of resistance for your potentiometer and photoresistor.
Two inverters
- pin 14 goes to voltage source
- pin 7 goes to ground
- R1 = 10k (resistor between pin 1 and pin 2)
- R2 = 10k (resistor between pin 3 and pin 4)
- C1 = .1uF (capacitor between pin 1 and ground)
- C2 = .1uF (capacitor between pin 3 and ground)
- R3 = 10k (resistor between pin 2 and OUT)
- R4 = 10k (resistor between pin 4 and OUT)
- The hot tip of the audio jack connects to OUT
- The sleeve of the audio jack connects to ground
Step 5: Use Two Inverters
To connect multple inverters to the same audio output, send each signal through a 10k resistor which all terminate at the hot tip of the audio jack. To play with the signal, could substitute R1 and/or R2 for variable resistors like a potentiometer or photoresistor.
Step 6: Use Three Inverters
Step 7: Use Three Inverters
This time use a 10k resistor for inverter #1, a potentiometer for inverter #2, and a photoresistor for inverter #3.