Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Need help with an LED setup

Status
Not open for further replies.
The wizard calculates the resistor for each series string of 3 LEDs.
If you tell the wizard the highest forward voltage then if the LEDs actually have the lowest voltage they will burn out.
if you tell the wizard the lowest forward voltage then if the LEDs actually have the highest voltage then they will be dim.
Try both ways with the wizard.

They are rated at 20mA to 30mA so use 25mA.
 
Ok, I got it. Well, looks like I'll be able to get all the resistors I need for under $10. Should have everything together done by the end of the month (going on vacation next week), and when it's done I'll post pic(s). :)

I have two more questions. One: I'm going to wire everything together (not solder yet) and test it with a 9v battery to make sure all the lights are turning on. Will that damage my lights at all, or will it be ok if I do it for just a few seconds?

I have two switches, as I want to be able to turn either the orange and blue lights on, or turn the entire circuit off. It's probably rather simple, but I can't figure out how to rig that.

**broken link removed**
 
The strings of blue LEDs and their current-limiting resistors need a 12V supply. They might not light with a 9V battery.
The strings of orange LEDs will light dimly with a 9V battery.
 
Actually since you want to light one color or the other you may want a SPDT switch with an Off center similar to this switch. Using a SPST switch you would have to manipulate 2 switches (turning one off and the other on and visa verse). Again, as AG stressed the circuit should be built around 12 volts. If you use 9 volt batteries like a PP3 standard everyday 9 volt battery the batterys will be short lived and as mentioned likely won't work.

Ron
 
I'd only be using the 9v to test the string before I get the resistors, as I will have to wait 2 weeks to get those and the batteries online.

I am thinking of getting a differing switch too.
 
As to switching see the attached. It shows the options for SPST and DPST.

As for the battery. Figure it this way. At any given time you will have 12 LEDs glowing happily away. The suggested configuration is 4 series strings of 3 LED EA. The series string current will be about 25 mA. So you can figure a battery drain of 100 mA for any given set of LEDs on. You want a choice of battery that will afford decent run time and yet fit physically into the scheme of things.

Have an enjoyable vacation. I am looking forward to my annual "Ron Trip" as my wife calls it. The end of May I go visit old friends for a few weeks. Then mid summer the wife and I will get away and then in September or October the annual "Kathy Trip" when she visits a cousin in Arizona. Anyway, have a good and safe time of it.

Ron
 

Attachments

  • switches1.gif
    switches1.gif
    8.5 KB · Views: 143
Last edited:
Thanks for all y'alls help! I don't think I would have been able to do this without it...I'm not that experienced with electronics so it was somewhat daunting, now I think I have it all figured out. :)
 
I'd only be using the 9v to test the string before I get the resistors.
A 9V battery probably does not have enough voltage to light 3 blue LEDs in series since each LED might be 3.6V then they need at least 10.8V.
But 3 orange LEDs need a total of only 5.4V so connecting them to a 9V battery without using a current-limiting resistor will fry them very quickly.

The extremely important resistors limit the current. It is unlimited current that burns out an LED.
 
Led

Hello I am hooking up 36 white led the power supply will be 14 volts dc what is the best way to hook them up and what Resistor or how many will i need
thanks
 
Do you have the specifications on the LEDs? Things like the forward voltage and current for the LEDs? White LED doesn't say much so there is nothing to work with.

Ron
 
One way to do it would be per the attached. Since you did not provide a forward current I winged it using 220 Ohm series resistors. That is based on Ifwd of 20 mA give or take which would be about 205 ohms. A common resistor is 220 Ohms. This is based on the 14 volts you mention. If this is an automotive application then all bets are off as the voltage will vary. Also if these are not 20 mA LEDs all bets are off also.

Ron
 

Attachments

  • 32 LED Config.gif
    32 LED Config.gif
    15.8 KB · Views: 158
IT is 3.3 volts for the led the normal every day led .
A white LED with a "typical" forward voltage of 3.3V will be somewhere from 3.1V to 3.5V. You can use 3 in series and in series with a 180 ohm resistor. Then 3.1V LEDs will have a current of 26mA, 3.3V LEDs will have a current of 23mA and 3.5V LEDs will have a current of 19mA.

That is one string of LEDs. Make as many strings as you need.
If you are guessing that a car battery is always 14.0V then it isn't. When the battery drops to 12.6V then the LEDs will be dim.
 
Led

I don't have the package that the leds came with had them for a while. but i have a ac power supply that converts to 14 volts Dc. so its all the time 14 I hope :) But i a'm using it for a light at the house 36 leds in it so can i do a res and a string of 6 and keep going that way? all pos to pos and all neg to neg right ?
Thanks
 
Nobody makes a 3.3V LED and you cannot order one. They have a range of voltages, from about 3.1V to about 3.5V for one that is "typically" 3.3V. I would use three in series with a 200 ohms resistor for one string and make many strings.
A normal 5mm LED works fine at 20mA to 25mA.
 
You can't do strings of 6. A string of 6 would be about (3.3 * 6 = 19.8 Volts/string). That is why I used strings of 3 with a 220 ohm current limiting resistor per string. Also, per AG, a 200 Ohm resistor would also work fine.

Ron
 
Last edited:
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top