How to make a blinking LED

Flashing LEDs are often used in various signal circuits. Light-emitting diodes (LEDs) of various colors have appeared on the market for a long time, which periodically blink when connected to a power source. No additional details are needed to flash them. A miniature integrated circuit is mounted inside such a LED, which controls its operation. However, for a novice radio amateur it is much more interesting to make a blinking LED with your own hands, and at the same time to study the principle of operation of an electronic circuit, in particular flashing lights, to master the skills of working with a soldering iron.

How to make a LED flasher with your own hands

There are many schemes that can be used to make an LED blink. Flashing devices can be made both from separate radio components and based on various microcircuits. First, we will look at the flasher circuit of a multivibrator on two transistors. The most common parts are suitable for its assembly. They can be purchased in a radio parts store or "obtained" from obsolete televisions, radios and other radio equipment. Also in many online stores you can buy sets of parts for assembling such circuits of led flashing lights.

The figure shows a diagram of a flasher of a multivibrator, consisting of only nine parts. To assemble it you will need:

  • two resistors 6.8 - 15 kOhm each;
  • two resistors with a resistance of 470 - 680 ohms;
  • two low-power transistors with an n-p-n structure, for example KT315 B;
  • two electrolytic capacitors with a capacity of 47-100 μF
  • one low-power LED of any color, for example red.

It is not necessary that paired parts, such as resistors R2 and R3, have the same value. A small range of ratings practically does not affect the operation of the multivibrator. Also, this LED flasher circuit is not critical to the supply voltage. She confidently works in the voltage range from 3 to 12 volts.

The flasher circuit of the multivibrator works as follows. At the moment of supply to the power circuit, always one of the transistors will be open a little more than the other. This may be due, for example, to a slightly higher current transfer ratio. Let the transistor T2 open more initially. Then, through its base and resistor R1, the charge current of the capacitor C1 will flow. Transistor T2 will be in the open state and its collector current will flow through R4. On the positive plate of the capacitor C2, connected to the collector T2, there will be a low voltage and it will not be charged. As C1 charges, the base current T2 will decrease and the collector voltage will rise. At some point, this voltage will become such that the charge current of the capacitor C2 will flow and the transistor T3 will start to open. C1 will start discharging through transistor T3 and resistor R2. A voltage drop across R2 will reliably close T2. At this time, current will flow through the open transistor T3 and resistor R1 and LED1 will light up. In the future, the charge-discharge cycles of the capacitors will be repeated alternately.

If you look at the oscillograms on the collectors of transistors, they will look like rectangular pulses.

When the width (duration) of rectangular pulses is equal to the distance between them, then the signal is said to have a meander shape. Taking oscillograms from the collectors of both transistors at the same time, you can see that they are always in antiphase. The duration of the pulses and the time between their repetitions directly depend on the products of R2C2 and R3C1. By changing the ratio of the pieces, you can change the duration and frequency of the LED flashes.

To assemble the flashing LED circuit, you will need a soldering iron, solder and flux. As a flux, you can use rosin or liquid soldering flux available in stores. Before assembling the structure, it is necessary to thoroughly clean and tin the terminals of the radio components. The terminals of the transistors and the LED must be connected in accordance with their purpose. It is also necessary to observe the polarity of the electrolytic capacitors. The marking and purpose of the terminals of the KT315 transistors are shown in the photo.

Flashing LED on one battery

Most LEDs operate over 1.5 volts. Therefore, they cannot be ignited in a simple way from one finger-type battery. However, there are LED flashing light circuits to overcome this difficulty. One of these is shown below.

In the LED flasher circuit, there are two capacitor charging chains: R1C1R2 and R3C2R2. The charging time of the capacitor C1 is much longer than the charging time of the capacitor C2. After charging C1, both transistors open and the capacitor C2 is connected in series with the battery. Through transistor T2, the total voltage of the battery and capacitor is applied to the LED. The LED lights up. After the discharge of the capacitors C1 and C2, the transistors close and a new cycle of charging the capacitors begins. Such a flasher circuit on LEDs is called a voltage boost circuit.

We examined several schemes of LED flashing lights. Collecting these and other devices, you can not only learn how to solder and read electronic circuits. At the exit, you can get quite workable devices that are useful in everyday life. The matter is limited only by the imagination of the creator. Having shown ingenuity, you can, for example, make a signaling device for an open refrigerator door or a direction indicator for a bicycle from an LED flasher. Make the eyes of the soft toy blink.

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