Build a Simple Touch Circuit Doorbell

Created by: Aakash Bathini
Edited by: Satyam Goyal

This DIY project will teach you how to build your own touch doorbell on a PCB using your finger to complete the circuit. We used two non-insulated wires that are connected to the transistor. When we touch the wires, the circuit is completed by our skin since it has some resistance in ohms. A small amount of current passes through the wire, triggering the transistor to switch ON the buzzer.

To begin it is important to know the basics of how a breadboard is structured. Consider the following diagrams and keep them in mind when creating your breadboard project.

Doorbell Diagram

Review the parts list below and once you have all your materials organized, you can start the building process.

Parts List

(1) Transistor BC547B TO-92 Transistor NPN Switch
(1) Magnetic Buzzer 5 Volt DC 30mA 2300Hz 85db 2-Pin
(1) 9V Battery Snap Holder with 10 Inch Wires
(1) 9V Energizer® Alkaline Battery
(1) 400 Point Solderless Plug-in Breadboard with 4 Power Rails
(1) Resistor Carbon Film 1k Ohm 1/4 Watt 5%
(1) LED Red Diffused 3mm (T-1) 635nm 8.7mcd 60VA
(4) Insulated Jumper Wire
(2) Non-Insulated Jumper Wire

Tools: Wire Cutters

Step 1 Transistor Connection

Doorbell Transistor

Connect the BC547B Transistor horizontally onto the breadboard with the emitter to the left, as shown above. Next, place an insulated jumper wire vertically connecting the emitter to the negative rail. Then, place a non-insulated jumper wire vertically from the base over the center divider. Place a second non-insulated wire connecting the collector of the transistor over the center divider.

Step 2 Magnetic Buzzer

Doorbell Buzzer

Place a horizontal insulated jumper wire starting from right under the collector. Then, attach the negative pin of the 5V Magnetic DC Buzzer (says on buzzer) under the jumper wire and the positive pin under the center divider. Then, attach a vertical insulated jumper wire connecting the positive pin of the buzzer to the positive rail.

Step 3 Connecting the LED

Doorbell LED

Next, connect the negative pin or cathode (smaller pin in length) of the LED in between the insulated jumper wire connected to the collector and the negative pin of the buzzer. Attach the positive pin or anode of the LED to a hole on the same letter strip.

Step 4 Adding the Resistor

Doorbell Resistor

Next, connect one end of the 1k resistor to the positive pin of the LED. Connect the other end of the resistor to any hole.

Step 5 Attaching Power

Doorbell Power

Connect the right-side pin of the 1k resistor to the positive rail by using an insulated jumper wire. Then attach the battery connector to the 9V battery by snapping it into place. Place the red lead of the battery connector onto the positive rail and the black lead onto the negative rail.

Final Results

Doorbell Final Result

Touch the two non-insulated wires either with your fingers or scissors (make sure to touch both). The LED light should turn on, and the buzzer should make a noise. If it does not work, some common errors could be the incorrect placement of the transistor pins, anode/cathode of the LED, and the direction of the buzzer.

For more information, watch the video below!