×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Alot of HELP with LED Project Welcomed!!! :)

Alot of HELP with LED Project Welcomed!!! :)

Alot of HELP with LED Project Welcomed!!! :)

(OP)
OK, First off let me say that my E-skill at best is minimum! I have searched high and low for information to help me with this project and I am on information overload I think! I have read every thread in the forum relating to "LED" as keyword and have found a few points that might help, but right now, I think I have bit off more then my share taking on this one but here it goes...

These are the LED's I am working with:
 
7- orange- VF 1.7v @ 20mA
8- UV-     VF 3.6v @ 20mA
1- Red-    VF 1.7v @ 20mA

As for power I was figuring on a 5v PS (but flexible... what ever is best!)

I would like to build a circuit that when a tactile button is pushed it would have the Red LED light up immediately and stay on. Then in 2 seconds intervals have each of the 7 orange LEDs light up and stay on (LED1, 2secs, LED2, 2secs, LED3, etc). Then after all the orange LEDs are on have the 8 UV LEDs turn on and stay on for about 5 seconds and then have all the LEDs shutoff, until the button is pushed again to repeat the process.

Note* As for Electronic terminology... lol... I have a dictionary around here somewhere! I just need to be pushed...or shoved in the right direction on this one. In my defense I have completed many projects when given even semi-decent instructions. Any help here will be welcomed... GREATLY!! Thx in advance!

RE: Alot of HELP with LED Project Welcomed!!! :)

You won’t find much anywhere related to "LEDs" to help you because frankly that is not the problem. Let’s suppose you decide to use the 5V power supply. Turning on the LED consists of connecting it across the power rail through a resistor to define the current.

Let’s take the orange LEDs.
VF is 1.7V. Ok so that means  5 - 1.7 across the resistor, provided the switching device doesn’t ‘lose’ (drop) too much voltage. You want 20mA so that means a (5 - 1.7)/(20E-3) = 165 ohm resistor. You might pick 150R, 160R, 180R depending on what is conveniently available.

If you can’t repeat this process for the other colours then give up

That was the easy bit. Now comes the circuitry to switch the LEDs. As you are a computer guy you might like to program the function into a PIC micro-controller. Of course if you don’t have access to a PIC programming interface, compiler etc, this option is impractical.

In that case you need to get a bit more ‘technical’. There are probably many ways to implement this complex function. Here is my first thought. The switch starts a ramp generator. This consists of an opamp wired as an integrator. You will find this configuration in application notes and so forth. The ramp ramps up slowly. I would suggest ±12V or ±15V power rails for this approach.

Suppose the ramp goes at a rate of 0.5V/second. You set level comparators at 1V intervals and when a threshold is crossed a new LED comes on. We are now talking about resistive dividers from the power rail to set the threshold levels and say quad comparators in 16 pin packages. The ramp will do all the timing; all you have to do is set thresholds and act accordingly.

This is not a complicated problem for an EE, but for a non-EE could be challenging. You have to be able to use transistors on the comparator outputs because one comparator will not drive 8x UV LEDS (=160mA). You could use a power MOSFET for this function, controlled by the comparator.

If you look at comparator data sheets you should see how to apply them.

You can also get thermometer bar code display chips which will do some of the work for you.

RE: Alot of HELP with LED Project Welcomed!!! :)

Another thought for the control circuit -- use a 1-second clock and a digital counter to drive the LED's.  Probably not the cheapest way to implement this thing, but it'd be easy.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources