The article illustrates a simple yet innovative, fancy car turn signal light circuit which produces a rising bar graph sequence effect when switched ON.
The circuit idea was requested by Mr. +Bruce Lowry. Let's learn more.
Technical Specifications
I am after a circuit design similar to the LED Bar Graph circuit that is found on this site/blog.
What I want to develop is a front turn signal sequential flasher that illuminates and holds the lights from top to bottom and then cycles them again and again until the turn signal is turned off.
I need to drive exactly 12 Amber LED's that drop 1.8 volts per LED. The LED's are laid out from top to bottom as such.
- 1 (number of LED's)
- 1(number of LED's)
- 1(number of LED's)
- 2(number of LED's)
- 3(number of LED's)
- 4(number of LED's)
I would like to illuminate the first one at the top and hold and then move on to the second one down and so forth until all 6 rows which consist of 12 total LED's are illuminated and then start the sequence over.
Variable resistors should be included so that the clock frequency can be altered. This will allow me speed up or slow down the illumination and hold of the LED's.
Plus if there is a variance in the driver side circuit and the passenger side I could use the adjustability to "syncronize" the working rates of both sides. (turning on the hazard flashers to observe both sides being enabled and sequencing would be a good way to visually check this)
In the connector to the front turn signals I am working with three connections.
Top pin is 12 volts constant when running lights are turned on (oh, just a thought- It would be nice to use the entire string of LED's as running lights as well) Middle Pin is zero volts (GROUND) and lower pin is 0-12 volts when the turn signal is activated.
I need a working circuit that will handle automotive voltages that are not always 12 volts in practice , but can range up to 14 or so volts in actual real world use.
A complete circuit diagram would be helpful. Including resistor values for driving the different multiples of LED's and if each LED would have its own resistor or just run them in series with one resistor.
Thank you.
The Design
The above circuit can be built using two different types of circuit configurations. One which uses the IC 4017, and the other through the IC 74LS164. Here we'll discuss the one which uses the IC 4017.
As shown in the first circuit diagram, the entire design is wired around the IC 4017.
We know that the IC 4017 which is a johnsons divide by 10 decade counter/divider chip produces sequencing high logic pulses on its outputs in response to clocks applied on its pin#14.
In response to each high pulse on pin#14, a high logic shifts from one output to the next in the following pin-out order: 3-2-4-7-10-1-5-6-9-11.
Thus all the 10 outputs become high sequentially until the last pin#11 becomes high after which the sequence returns to pin#3 so that the cycle can repeat yet again.
The cycle keeps repeating as long as the clock pulses are sustained at its pin#14.
However the sequencing pattern does not keep the outputs illuminated while shifting. The outputs become high and then become low again as the sequence shifts from one pin out to the other.
It means at any instant only one output is high during the sequencing process.
If we connect 10 LEDs at the above 10 outputs of the IC 4017, it would provide an impression of a single LED chasing effect, however since for the present car turn signal application we want a bar graph kind of appearance we would want the LEDs to stay and hold their illumination as the sequence proceeds from the start to the finish pin-outs.
To implement this "hold" feature we need to introduce a latching feature with the given outputs.
This can be simply done with the use of SCRs, because as per the characteristics SCRs latch their MT1, MT2 leads if the supply is a DC. Therefore it perfectly suits our application.
By connecting SCRs at the first 6 outputs of the IC we can simply implement the bar graph kind of feature such that the LeDs hold and stay illuminated until the complete is completed.
Pin#1 provides the last sequencing output after which the IC should shut down all the LEDs and begin the procedure all over again.
For actuating the above action, the transistor T1 stage in introduced at the next pin#5, which instantly inhibits the supply voltage to the SCrs so that all of them shutdown.
Pin#6 is tied to the reset pin#15 of the IC which makes sure the sequence gets back to pin#3 as soon as the LEDs shut OFF, enabling the next cycle to commence.
Circuit Diagram
As rightly expressed by Mr. Bruce, the above circuit will not function properly under a fluctuating DC which would be normally available across the existing turn signal light outputs due to switching of the flasher relay.
Adding a Delay Timer
However the above circuit can be simply modified by adding a small time delay circuit, which would hold the current and keep the circuit functioning switched ON by supplying the required amount of power during the absence of supply from the flasher relay.
The above sequential car turn signal light circuit was successfully built and tested by Mr.Bruce Lowry.
The wonderful results can be witnessed in the following video. Please refer to the comments to learn regarding the whole process.
With an adjustable rate of flash added, the circuit now looks much enhanced. Courtesy: Mr.Bruce Lowry.
The above design was further modified by Mr. Jason in order to implement additional specific actions such as making the LEDs stay solid when the brakes are applied, but also making sure that the LEDs stayed in the flashing/running mode in case both: the turn signal and the brakes were switched ON together or simultaneously.
Video Clip of the prototype:
Another Clip:
Modifying Further
The modified design which is attached below has an additional feature wherein the LEDs could also be used as park lights thereby making the above circuit a 3 in 1 unit:
Here's the complete design drawn by Mr. Jason for your viewing pleasure:
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