Description
Are you interested in how to design DIY sequential turn signals? In this episode of House of Hacks, Harley shows a unique design using a couple components to create a tail light sequencer circuit.There's now a follow-up post with links to block diagrams for this project.
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For a written transcript, go to How to design your own DIY sequential turn signals
Music under Creative Commons License By Attribution 3.0 by Kevin MacLeod at http://incompetech.com.
Intro/Exit: Hot Swing
Transcript
Interested in sequential turn signal indicators?Today at the House of Hacks we'll be looking at exactly that.
[Introduction]
Hi! Harley here.
I have a car that has three tail lights on each side and the manufacturer has those coming on all at the same time, for both brakes and turn signal indicators.
And I thought I'd be cool to change that so it would be sequential turn indicators. Kind of like the old Cougars and Mustangs had.
There's a lot of ways you could design a circuit like this.
I believe the old Cougars, and probably the Mustangs too for that matter, had mechanical switches that had a motor driven swiper on them.
And so as that swiper turned, it would have different contacts that would turn the lights on in sequence.
You could also use various timer circuits from RC circuits to 555 timers to anything else that you really wanted to to provide a timing mechanism and then use either transistors or logic circuits to control the sequence turning on.
And of course you could also use micro-controllers like a PIC or an Arduino to accomplish the same task.
When I first started thinking about this project a number of decades ago, a friend of mine, Robert Largent, suggested using an EPROM to store the different patterns in and just use a timer to increment the bottom two address lines and then use higher address lines to switch between Brake, Left, Right indicators.
I built the circuit and it worked great and I've had it sitting around in a box until I get around to rebuilding that car.
I'm a member of a Facebook electronics design group and somebody asked a question, in kind of an ambiguous manner, about LEDs and EPROMs and it reminded me of this project, so I went and dug it out of the box.
This is really just going to be a design overview. I'm not going to go into the details of constructing the circuit or the schematics, but I will talk about it on a block level diagram perspective.
Let's take a closer look at this.
OK. Let's talk about EPROMs for a minute.
There's two types of EPROM. There's serial EPROMs and parallel EPROMs.
The serial ones are designed for serial interfaces, particularly with micro-controllers and things like that and they don't lend themselves to this project.
This project uses parallel EPROMs which are characterized by having multiple address lines coming in and multiple data lines coming out.
Usually you have eight data lines out and any number of address lines going in depending on the size of the EPROM.
Typically we think about an EPROM as you give it an address and you get data out.
Another way of looking at it, which is kind of the same thing, but a little bit different, is you have status inputs and you have status outputs.
It's really kind of the same thing but it's looking at it from a slightly different perspective.
Instead of looking at it through a sequential address space thing like a computer would normally use it, you're looking at it from a input mapping to an output table perspective.
And that's how this project approaches it.
You need an EPROM that has at least five data lines. In this particular case I think it has eight for 256 memory locations.
(I'm not positive on that.)
And you also, for this particular project, need at least six data lines.
I think all of them have a minimum of eight data lines because that's just kind of the typical size of a byte for a computer, so you usually don't have to worry about the data output side, it's more the address input side, depending on the memory size.
The way I have this EPROM setup is there are multiple blocks of four groups.
The four groups correspond to the Off state, the 1 LED state, the 2 LED state and the 3 LED state.
And those four states are just replicated for each of the combinations of Right turn, Left turn and Brake that are possible.
OK, so let's look at the circuit itself.
It's really broken up into a couple different sections.
Power can be 12 volts in a car system normally and the logic circuit needs to run on 5 volts. So we have a little 5 volt regulator here to power the circuit with.
And then we have three input lines. Again, the car is typically 12 volts and it's easiest if we deal with 12 volts on the input side coming from all the switches so we don't have to have 5 volt regulation anywhere else in the car.
So we have red is Right, black is Brake and green is Left turn indicators. All those can be up to 12 volts and then we have a little bit of conditioning circuitry here to drop that to 5 volts.
That's going into the address lines for the EPROM, this large chip being the EPROM. Those are going into the A2, 3 and 4 lines for the EPROM.
Then we have a 555 timer here that is adjustable. It has a little rheostat that I can adjust the timing on.
And it's going into a binary counter. So the binary counter has a clock that's going up and down and it just counts the pulses on that.
So this will convert the clocked pulses into a number that corresponds to 0, 1, 2, 3, 4, it'll actually count up to... I'm not sure how high this particular chip counts, but it counts up to a certain point and then it rolls over and starts back at zero.
Since we're only dealing with two bits to count from zero to three, which gives us our four states for our three lights, we really only care about two of those output lines.
If you put it on output bits 0 and 1 and connect that to address lines 0 and 1, you'll run this clock at the same speed as the 555 timer.
If you change your output bits that you're using on your counter from the bottom two, every time you shift up one output, you're dividing the speed of your counter by two.
So it's easy to get divisions of two on your timer, but then you can also adjust your timer speed, so you have lots of flexibility in terms of how fast this thing cycles through your bottom four bits.
Then we have the bottom six bits of the memory going over to this other board which is basically just designed for high current switching.
It's going into a buffer over here which will eventually be connected to transistors so we're not driving the transistors directly from the EPROM but we're buffering it through a device that can handle that kind of switching more easily.
Then I also have the outputs of this buffer going to these LEDs with some current limiting resistors over here so we can just kind of see the status of that.
Ideally in the future I'll put some transistors along this section that will then control the incandescent lights in the car, if I so choose that way, or I might drive a high-current LED panel to get a little bit more modern look to it.
That's the basic overall system design.
You can see right now I have it setup with the Brake and the Left turn indicator going.
If I disconnect the Brake, now we just have the turn indicator.
If there's nothing going, we have nothing.
We can look at the right turn indicator if I connect that here.
We have just Brakes only, they all come on.
Then if I connect both the turn indicators, we can see the hazard conditions.
Now the interesting thing about this... most cars when you have hazards on and you have brakes, you get one of two conditions. Either it's designed so you get just the hazards and the brake is ignored. Or you get brakes and hazards are ignored. But you don't really have a state indicating both brakes and hazards.
Now with this design, you can actually put anything in those memory spots you want to get any kind of pattern.
In this particular case, I've set it up so that when you have hazards and brakes combined, you actually get all the lights blinking on and off, which is different than hazards or brakes, either one by itself.
So that gives you a little bit more flexibility in this design.
You could also have it setup so that the lights alternate back and forth or any other type of pattern that you want besides just this.
So I happened to choose all blinking like this for that case but you could do anything you want.
But the point being it can be separate from the hazard case and the brake case, which is a little bit different than standard sequential light circuits.
I hope you found this design overview interesting and if you're interested in electronics and photography, wood working, metal working and other shop related projects, I encourage you to subscribe and click the bell notification icon and YouTube will let you know next time I release a video.
Until then, go make something.
Perfection's not required.
Fun is!
