Lesson 4 — Electronics for kids — Wave for a buzzer

Rahul Agarwal
3 min readMar 8, 2023
Buzzer and LDR

This story is part of a series. See this starting page for links to other lessons.

In this lesson we continue to learn about transistors. We modify the experiment in Lesson 3 and add a light detecting component and buzzer so that waving your hand activates the transistor and thus the buzzer and LED.

Please see previous posts for components we have already used in the past. The new components we will use are a buzzer and a light dependent resistor (LDR). A buzzer simply makes a buzzing sound when powered. The buzzer is purely to add something new and not necessary if you don’t have one handy. The LDR or a photoresistor is a type of resistor. We had previously discussed a resistor as the electrical equivalent of squeezing your garden hose to reduce the flow of water. The larger the resistance the lesser the electricity flowing past it.

In the LDR, the presence of light reduces the resistance and more electricity flows. So if you cover it (dark), electricity should not flow (and no light/buzzing sound). If uncovered (light on LDR) electricity should flow and turn on the buzzer and LED.

The circuit is similar to Lesson 3. Instead of sending power directly to the base of the transistor, we now control it with a LDR.

Have the child explore the new components and then try to connect as shown. Help them by pointing to the numbers on the breadboard to connect wires/components.

Breadboard visual for circuit to enable a transistor with a LDR
Breadboard visual for circuit to enable a transistor with a LDR
Circuit diagram to enable a transistor with a LDR
Circuit diagram to enable a transistor with a LDR

No power to the buzzer and LED when the LDR is covered.

Covered LDR opens the circuit
Covered LDR opens the circuit

Exposing the LDR closes the circuit and the LED lights up and the buzzer sounds.

Uncovered LDR closes the circuit
Uncovered LDR closes the circuit

Tip: make sure the buzzer “+” and “-” are connected correctly. Also the transistor collector, base and emitter but be connected to the right pins.

Tip: Ideally you have multiple breadboards and you can save this experiment. We will reuse Lesson 4 and Lesson 5 in Lesson 6.

This story is part of a series. See this starting page for links to other lessons.

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