How does an indicator cancel itself?
Answers to this and few other mind-boggling questions about blinkers.
Indicators, where would we be without them? Since 1939, when they were first implemented in regular cars, they've probably saved hundreds, if not thousands of lives and prevented millions of dollars' worth of damage. However, despite the importance of this invention, many people still don't know how does an indicator work. So, to satisfy your hunger for knowledge, let's dive into the inner workings of the blinker.
I mean, where would we be without blinkers? We would probably only go straight or we would have a lot more crashes. It's a good thing Buick introduced them to regular cars.
Why does a blinker blink?
In principle, an indicator works as any other light in a car. Turn signal switch, which is usually a lever attached to a steering column, allows electricity to pass through to power either left or right-hand blinkers.
However, a blinker that isn't blinking isn't a blinker, it's merely a light. To allow an indicator to turn on and off periodically, manufacturers developed a device called a thermal flasher. It works as follows: upon switching on an indicator, current passes through a resistor. As a result, this resistor heats up, which also raises a temperature of a piece of specially designed steel located in a close proximity of the resistor. After one second or so, this piece of steel warms up and expands enough to make contact with wires, essentially bypassing the resistor and allowing blinkers to turn on (they are off when the current passes through the resistor as voltage is too low for them to shine). As there is no current passing through the resistor at this point, it quickly cools down, and so does the piece of steel. After another second, it is no longer warm enough to make contact with wires, so the current now passes through the resistor and a cycle repeats itself.
Did you know that when your turn signals stopped working, you should signal your turns with hand gestures, as you would do whilst cycling?
What makes a clicking noise?
Clicking noise is directly associated with the aforementioned thermal switch itself. Initially, the sound was a result of a recurrent engagement and disengagement of the metal piece on the wire itself. However, this solution is rarely used nowadays, as the technology has advanced quite a bit since blinkers were invented.
Instead, manufacturers use electronic relay style systems, which are favoured due to their robustness and probably lower cost as well. Such systems send current to indicators and a small electromagnet that acts on a switch-like thingy integrated in a circuit. When the electromagnet pulls the switch close enough, it breaks the circuit, so indicators turn off. However, so does the electromagnet and it is no longer acting on the switch-like thingy, allowing it to return back to its original position. This makes the current pass through the switch to the electromagnet and blinkers and the cycle repeats itself, allowing blinkers to happily blink. In such system, sound results from the back and forth operation of the switch-like thingy.
In some modern cars, the switches are silent, which means that there is no physical movement that would produce the clicking noise. Instead, sound usually comes from speakers to remind the driver that the indicators are on. Some manufacturers go as far as to allowing you to choose the sound of your blinkers. Take a listen:
How does an indicator cancel itself?
Self-cancelling turn signals seem obvious nowadays. However, even as late as of 80s some Citroëns didn't have this feature. Brand argued that turning off the indicators should be a conscious decision of a driver and shouldn't happen automatically. Luckily, probably all of the cars produced today come with self-cancelling turn signals (you can correct me if I'm wrong). So how does an indicator actually cancel itself?
In essence, there are usually four notches on a steering column of a car. As you switch on your turn signals, a small spring-loaded cylinder falls into one of these notches. In the same time, a plastic lever engages with the notches as well. As you turn a steering wheel, the plastic lever slides over grooves in the steering column and over the cylinder located in one of them. However, as you start turning the steering wheel the other way, plastic lever slides over the notches in such a way that it attempts to push out any objects located in them. When it engages with the cylinder, it forces it out of the notch, turning off the turn signals.
This is just a basic working principle. Cars may have some advanced features to allow you to make multiple revolutions of a steering wheel in one direction. However, this simplified model can explain the reason why indicators do not always turn off automatically. A small turn, like changing a lane on a motorway, might not be enough for the system to engage properly, requiring you to switch off your blinkers manually.
Citroën CX - quirky and beautiful styling, but the indicators didn't cancel themselves. By Alexander Migl - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=88133901
What we've learned
As you can see, indicators are a quite clever piece of engineering. They periodically blink and click thanks to a thermal switch or some sort of electronic relay system. Self-cancelling turn signals are a bit more complex, as they operate based on notches, springs and levers. Nonetheless, I hope you've learnt something new thanks to this article. If you want to know more about indicators, you can check out these pieces (piece one, piece two and piece three), which allowed me to understand the inner working of blinkers and to bring that knowledge over to DriveTribe.
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