LED Turn Signals
Seen those cars with fancy turn signals on their side view mirrors? Would you like to add something like that without buying a new car? Well, this circuit takes that idea a step further by generating a sequence of moving chevrons to create an animated turn signal. And, the circuit uses common logic devices instead of a microprocessor so no device programming is required.
The circuit uses a 9X7 array of yellow LEDs. Each 7-LED column is arranged in the shape of a chevron as shown below:
When the array is viewed as a whole it appears as:
The circuit is designed to be plugged directly into the turn signal bulb. So, when the turn signal turns on, the circuit turns on and illuminates the chevrons from left to right for the right side turn signal, and right to left for the left side signal. After the last pair of chevrons are illuminated, the circuits stops until the blinker signal goes from off to on again.
Designed around the venerated MC14017 decade counter IC, the circuit has a total of ten states:
|2||Illuminate chevrons 1 and 2|
|3||Illuminate chevrons 2 and 3|
|4||Illuminate chevrons 3 and 4|
|5||Illuminate chevrons 4 and 5|
|6||Illuminate chevrons 5 and 6|
|7||Illuminate chevrons 6 and 7|
|8||Illuminate chevrons 7 and 8|
|9||Illuminate chevrons 8 and 9|
These states appear as:
States 1 and 2
States 3 and 4
States 5 and 6
States 9 and 10.
After building the circuit, connect the signal called BLINKER SIGNAL to the high side of the turn signal bulb. Connect the ground signal to the low side of the bulb. A quick way to determine the low side is to measure the resistance between the chassis of the car and the bulb contacts with the car turned off. The low side, or ground, will have a very low resistance relative to the chassis. Once connected, turn on the car and then flip on the blinker. Clocking is provided by an adjustable 555 timer configured as an astable multivibrator which is another way of saying oscillator. With the blinker running, adjust R4 until each pair a chevrons turns on during the blinker on period. If you need less than nine columns then remove the unwanted columns from the right.
Note that for simplifying the schematic, the LED resistor network shown below is repeated for each chevron:
The circuit and the LEDs can be mounted to a simple prototype board. If your are retrofitting your car, I would suggest that you attempt to find some clear custom taillight covers for your vehicle. Not only will this add a unique element to your car it will save energy since it only uses a half of watt of power when two columns or 14 LEDS are on.