Flashing LEDs Circuit for Pedestrians using NAND Gates
This simple flashing LEDs circuit for pedestrians is very useful for people who like to walk at night. Two groups of high-intensity white LEDs are lit in turn, being easily visible at night.
Some people use phosphorescent colors clothes, in order to be more visible at night and avoid accidents by lack of visibility. This normally happens on streets with little or no light.
This circuit is suggested in order to further enhance the visibility of pedestrians. This device may be placed in any part of the body such as an arm.
How the flashing LEDs circuit for pedestrian works?
The circuit has of two parts:
– The first part is an astable multivibrator made with two 2-input NAND gates. The two NAND gates outputs of this multivibrator are applied to other two NAND gates that works as inverter gates (NOT gate). The latter gates are not necesary for the circuit to work, but they are used in order to have all gates of the integrated circuit to work.
– In the second part, each output of the latter gates is applied to a transistor through a resistor. These transistors constantly goes from the cut-off region to the saturation region, turning on and off the two groups of LEDs.
The oscillation frequency of the astable multivibrator can be modified by changing the values of resistors R1 and R2 and the electrolytic capacitors C1 and C2.
If you want to increase the intensity of light, change the groups of 2 LEDs in series by groups of 3 LEDs in series, removing resistors R6 and R7. The circuit is powered by a 9 volt battery for easy to carry on.
Keep in mind that if 3 LEDs are used instead of 2, the battery should not have a voltage lower than 9 volts, because the LEDs may not turn on or give very low light.
List of components for the flashing LEDs circuit for pedestrian
- 1 4011B IC (four two-input NAND gate) (IC1)
- 2 2N3904 NPN bipolar transistors (Q1, Q2)
- 4 High efficiency white LEDs (D1, D2, D3, D4)
- 2 470K, 1/4W resistors (R1, R2)
- 2 47K, 1/4W resistors (R3, R4)
- 1 1K, 1/4W resistor (R5)
- 2 330 ohms, 1/4W resistors (R6, R7)
- 2 4.7uF / 25V or more electrolytic capacitors (C1, C2)
- 1 switch (SW1)