LED Indicator Light
This circuit, being economical, can be used in place of blinking indicators in bikes or on the instrument panel in cars. The circuit uses the 555 timer IC for pulse generation and IC 7490 as the BCD counter. The LEDs, if positioned closely in the same manner as shown, appear to move in one particular direction when the frequency of pulses is increased. If the frequency is too high, all the LEDs appear to glow at the same instant.
The binary outputs of 7490 as it counts from 0 to 9 are given below:
| COUNT | Q3 | Q2 | Q1 | Q0 |
| 0 | 0 | 0 | 0 | 0 |
| 1 | 0 | 0 | 0 | 1 |
| 2 | 0 | 0 | 1 | 0 |
| 3 | 0 | 0 | 1 | 1 |
| 4 | 0 | 1 | 0 | 0 |
| 5 | 0 | 1 | 0 | 1 |
| 6 | 0 | 1 | 1 | 0 |
| 7 | 0 | 1 | 1 | 1 |
| 8 | 1 | 0 | 0 | 0 |
| 9 | 1 | 0 | 0 | 1 |
PARTS LIST
| VR1 | 100K |
| C1 | 22μ , 10V |
| IC1 | Timer NE555 |
| IC2 | BCD Counter 7490 |
| D1-D7 | LED |
| OTHERS | Battery 9 Volt and others |
CIRCUIT DIAGRAM
CIRCUIT Descriptions
If the LEDs are connected across the output, '1' indicates that the LED lights up. Here '1' appears to be moving lefts as counting progresses. Hence the light appears to move left if the counter is fast enough so that individual flickers are not visible.
IC 7490 has been used instead of IC 4011 since the circuit can also be used to check if the ICs 7490 (or 7493) are good.
It is interesting that a digital IC specifically designed for binary counting can also be used in a project entirely different from the one for which it is intended.
Project Submitted By : RAMESH R.
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