Red Jumbo LED Flasher - Breadboard Kit

Description: Red Jumbo LED Flasher - Breadboard Kit
Skill Level: Beginner
Assembly Time: 20 minutes

Red Jumbo LED Flasher Two jumbo 10mm LEDs flash in an alternating frequency that you can adjust with two potentiometers. This kit is also available in other colors Orange, Yellow, Green and Blue. This breadboard version is great for beginners to electronic circuit assembly. It is hands-on, and you can see how all the components and connections work together.

Scroll down for a simple set of instructions. Just stick the breadboard to page using the self-adhesive pad, and use the row/column instructions to assemble. If you're ready to test your hand at soldering, the same kit is available with a PCB. You may receive additional components for some parts depending on how they're packaged. Spare parts are always handy.

Kit Includes:

(1) 9V battery snaps
(2) BC547 transistor (Q1, Q2)
(2) 500kΩ potentiometer (R5, R6)
(2) 10μF, 50V electrolytic capacitor (C1, C2)
(2) 1kΩ resistor (R1, R2)
(2) 10kΩ resistor (R3, R4)
(2) Red diffused jumbo 10mm LEDs (D1, D2)
(1) 170 point breadboard, 1.9" x 1.3"
(10) 2" blue solid 22 AWG pre-formed jumper wires
(1) 9V battery Breadboard

Step 1 – The Breadboard

Breadboards are great for building simple circuits. Component changes are easy since none of the connections are permanent. The number of holes is usually listed as contact points or tie points. The channel running down the length of the breadboard is called a terminal strip, and it isolates one side from the other. Some breadboards can have more than one terminal strip. It is typically where you install DIP ICs and it allows them to have isolated rows for each pin.

Some breadboards have bus strips and are typically two columns; one for ground (blue) and one for power (red). This gives you close access to power and ground connections. The breadboard used in the project does not have bus strips, but it has one terminal strip. The five pins across a row are interconnected.

Step 2 – Review The Components

You should make sure you have all the components required before beginning. If the parts are not labeled, you can either read the markings on the component, or you can use the color code listing in the step for the resistors.

Step 3 – The Schematic

The schematic diagram is the most basic representation of a circuit. It uses universal graphic symbols to represent the components. The top line connected to the battery is the positive side and the wire running on the bottom is the ground connection.

The polarized capacitor symbol shows which side is positive. The transistor (BC547B) has an arrow which indicates the emitter. More detail for each component is given in the step where they are used.

Given the many possible ways a circuit can be assembled on a breadboard, components and leads quickly overlap each other and it is difficult to illustrate in a step-by-step. Starting from the positive side of the circuit, you can assemble in the same manner from one side of the breadboard. Since the circuit is somewhat symmetrical having duplicate components, you can split each half of the circuit to one side of the breadboard.

Step 4 – Install 1kΩ Resistors

The resistors do not have polarity so they can be installed in either direction. Bend both leads down and connect one end to the row that will connect to the positive wire from the battery and insert the other lead about 4 or 5 rows down. This will give you room for other components and help spread out the circuit on the breadboard. Use a jumper wire to join both rows that will ultimately connect to positive power.

Install Resistors and Potentiometers

Step 5 – Install Potentiometers

Since one pin is unconnected on the schematic, you can install it in the board so the unused lead overhangs the board, or you can install it with all three pins in separate rows of the breadboard and just be sure not to connect anything to pin 1.

Step 6 – Install LEDs

The longer lead is the positive and the shorter is the negative lead. Since power is connected to one side of the 1k resistors placed in step 4, connect the positive (long) lead of the LED to the other end of the resistor.

Step 7 – Install 10k Resistors

Bend the leads of the resistor in the same way as the others. Connect one end to the same row as pin 3 of the potentiometer and install the other end of the resistor about 4 or 5 rows down to another row that is unused.

Install LEDs and Resistors

Step 8 – Install Capacitors

This capacitor is polarized and can only be installed in one direction. The capacitor has a stripe with the minus sign going down one side to show which lead is negative. The schematic identifies the positive lead with a "+" (plus sign). Install the negative lead in the row that now has the 10k resistor connected to it, and connect the positive lead to the negative lead of the LED. Using the image to the right as a reference, the one end of the 10kΩ resistor and negative lead of the LED are each in their own row. These rows are connected together via the capacitor.

Install Capacitors and Transistors

Step 9 – Install Transistors

Install Capacitors and Transistors A transistor is basically an electrical switch. In this case, the transistor will "collect" the signal from the LED and "emit" it to ground when instructed by a signal sent to the "base". Install the transistor so each lead has its own row. You will use jumper wires to make connections to the transistor.

Install a jumper wire from the row containing the negative lead of the LED and the positive lead of the capacitor to the collector (pin 1) of the transistor on the same side of the breadboard. Do the same for the transistor on the other side. Connect another jumper wire from the row containing the negative lead of the capacitor and 10k resistor, and connect it to the base (pin 2) of the transistor on the opposite side of the breadboard. This is what will allow the flash. Do the same for the other transistor base. Those should be the only wires that cross the board at this point. Connect a jumper wire to join the rows that contain the emitter pin (pin 3). Both emitters connect to ground, so they can share the same connection.

Install Battery

Step 10 – Install Battery Holder

The red wire on the 9 volt battery holder is for the positive connection. Connect the red wire to the first row where the 1k resistor and potentiometer center pin are connected. The black wire is for ground. Connect the black wire to the row containing the transistor emitters (pin 3).

Step 11 – Plug in The Battery

Plug in the 9V battery and the LEDs should begin to flash. Use a small screwdriver to adjust the tuning knobs/screws on the potentiometer. Each potentiometer will adjust the flash rate of one LED. As long as both adjustment screws are at the same position, the LED flash should be the same duration.


When you apply power to the circuit, the transistors will switch on and off causing the LEDs to flash in pulses. Let's assume when you first power up the circuit with the 9 volt battery, C1 has already charged up with 7 volts through the 1kΩ resistor at R1. Capacitor C2 is charging through the 500kΩ potentiometer at R6 and when the voltage reaches 0.7 volts, transistor Q1 turns on. The Q1 collector and the positive lead from C1 are pulled down to 0 volts which forces the negative lead of C1 to -7 volts which turns off transistor Q2.

Capacitor C1 is still connected to the positive 9 volts through the 1kΩ resistor at R1 and it makes the capacitor C1 charge in the opposite direction. The voltage on the negative side of C1 (and base of transistor Q2) starts to move from -7 volts toward the +9 volts. When the voltage reaches 0.7 volts, transistor Q2 turns on and the voltage stored in capacitor C2 turns the transistor Q1 off.

Capacitor C2 now charges in the opposite direction through the 10kΩ resistor at R4. The voltage on the negative side of C2 (and base of transistor Q1) now starts to rise toward the +9 volts but triggers Q1 when it reaches 0.7 volts. The circuit will now repeat being back where it started. The capacitor and potentiometer values are what determine the flash rate and the potentiometer varies the time the other transistor is off.

Easy Instructions

Step 1: 1K Resistor (brown-black-red)
R1: Insert one leg into D2, insert other leg into D6.
R2: Insert one leg into I2, insert other leg into I6.

Step 2: 10K Resistor (brown-black-orange)
R3: Insert one leg into C3, insert other leg into C7.
R4: Insert one leg into H3, insert other leg into H7.

Step 3: 500K Potentiometer
R5: Insert pin 1 into A1, insert pin 2 into B2, insert pin 3 into A3.
R6: Insert pin 1 into F1, insert pin 2 into G2, insert pin 3 into F3.

Step 4: 10µF Capacitors (Note the stripe marking negative (-) side.)
C1: Insert long leg (+) into E10, insert shorter leg (-) into E7
C2: Insert long leg (+) into F10, insert shorter leg (-) into F7

Step 5: BC547 Transistors (Pin 1: Collector, Pin 2: Base, Pin 3: Emitter)
Q1: Insert pin 1 into E15, insert pin 2 into E16, insert pin 3 into E17
Q2: Insert pin 1 into F15, insert pin 2 into F16, insert pin 3 into F13

Step 6: Jumper Wires
Insert one end into C2, insert the other end into H2
Insert one end into B7, insert the other end into I16
Insert one end into I7, insert the other end into B16
Insert one end into C10, insert the other end into B15
Insert one end into H10, insert the other end into I15
Insert one end into B17, insert the other end into I17

Step 7: LEDs
D1: Insert long leg (+) into A6, insert shorter leg (-) into A10
D2: Insert long leg (+) into J6, insert shorter leg (-) into J10

Step 8: Battery Holder
Insert red wire (+) into J2, insert black wire (-) into J17

Step 9: Battery
Attach 9V battery and tune potentiometers to adjust alternating flash speed