EL wire to the speedometer

Hi people,

I'm currently trying to fix this in my project

The idea is simple = take the speed signal (square wave AFAIK), and somehow interface it to a EL wire LED which would then display the speed digitally.

What i'm unclear about is the interfacing between the speedometer and the 7-segment LED display. What decoder do I need to get in order to see the speed from the output, or am I looking at the whole thing wrong?

Can anybody jumpstart me? or point me somewhere.. :-/

you mention EL wire and a seven segment led display, is it a 7 segment made of el wire, or EL wire and a 7 segment led display?

Opss So sorry.. i mean the number display on the EL Wire nothing to do with the 7 Segment..

hmm, well your best bet might be looking into interrupts to count how many pulses you see in a given interval. you can use the metro library to check once a second for speed (or faster, doesnt matter). then the rest is just dividing by tens to take out individual decimal places and displaying them on your display.

crappy pseudo code ahead.

#include <Metro.h> //Include Metro library

int counter = 0;
unsigned long timecounter;
METRO calcpulse = Metro(1000);

void setup()
  pinMode(0, INTPUT);
  attachInterrupt(0, count, RISING);

void loop()
int pulsepersecond = 0;
if(calcpulse.check() == 1)
 pulsepersecond = counter
counter = 0; 

//do whatever calculations here that you need to turn the pulses into a speed using //pulsepersecond variable


void count()

Wow.. Thanks Thanks Gotta Digested that.. Anyone know how to connect the Speedometer onto the ProtoShield board..??

do you have any specs on the input signal?

Not that i have currently.

As i am going to Purchase 1 soon.Is there any Recommendation? but as far as i know the Speedometer show be in binary based and acts like a reed Switch..

It should not be wireless and It will be connected in 1 of the pin at the Protoshield board as an interrupt..

well, there's not really much left to do for the speedometer part. what kind of display do you have set up? is it EL wires arranged into a 7 segment display or is it an all in one module? any links to data-sheets or where you got it, or any model numbers may come in handy.


This is what i gonna Build..

Since you have discovered the Speed Vest project, you should also look at the code in their example to see how they calculate the speed from a sensor on the wheel. I imagine you could adapt that for your project, once you figure out the incoming data from your system.

But i am not sure how to connect the EL Wiress…

Ah, that I can help you with! I have done a similar project.

The circuit and code are in that Speed Vest project, although it did take me a while to figure it out myself. There have been other threads in this forum about it, and I even posted a little circuit digram for the EL wire connection.

Let me go look for it...

WOw!! Thanks Thank .. i seriously need help haha..

Here is a little picture of the basic circuit you need to power EL wire.

I don't know how far you've gotten in your research on this, but there is quite a lot of info in this forum, and also some in adafruit's, if you search for EL wire.

The key, since EL wire uses AC current, not the DC of the Arduino, is that you need a component called a triac to switch the EL wire current on and off. And you need an inverter to convert DC power (from a battery or the output of a wall wart) to the AC required by the EL wire.


Hi Andy,

As u know i will be creating the Speed vest and if u can see slide 2 from pg 102 (http://www.make-digital.com/make/vol19/?pg=102&search=vest&per_page=5&results_page=1&doc_id=-1) they connect the EL wires onto the 14 wire ribbon but as far as i know the EL Wires have a + and - node so where does the - node go? how to connect the ribbon to the EL Wires? :-/

I'm not 100% sure of this, but I think the polarity (+/- markings) on the EL wire doesn't matter. It's AC, not DC.

I had a similar experience as you with my EL wire project; enormous amounts of time to get the concepts down. Once I absorbed them properly, I was able to build my circuit easily.

The little diagram I posted, for connecting one EL wire to one Arduino pin (could have a shift register in between, but I didn't show that), is my distillation of those concepts. And it works to extend it to multiple EL wires.

Does it make sense?

But i need to convert the AC to Dc in this case does the + and - makes a different?

No, you don't convert AC to DC.

The AC only powers the EL wire. The triac in the circuit switches the AC on and off, depending on the voltage supplied to its gate, the third input from the left of my diagram, coming from the Arduino pin.

So, the triac is triggered by the DC voltage from a digital output pin on the Arduino and it allows the AC current to either flow through or not flow through the wires attached to its other two pins, which are one side of the AC line to the EL wire.

The inverter takes DC current from a battery or a wall wart and converts it to the right kind of AC that the EL wire needs.

However, what is even more confusing is that the AC and DC sides of the circuit do need a common ground. So one side of the AC is designated ground and is tied to the DC ground of the Arduino and one side of the triac.

Study my diagram; all of these words should be in there!

Make sense?

in another words i dont need to shot all the - together?

No, you DO need to tie all the grounds together.

Here is another schematic for how to connect two EL wires.

There is also a primer in the current issue of Make magazine on EL wire: http://makezine.com/21/primer/, but I haven't read it yet.