LEDs schematics

[saturnX]

hi guys, was just wondering if it were possible to tie a few LED's together onto one resistor? have a small project that i am working on for a friend but the space for the circuitry is limited. feedbacks welcome..

[rhino]

You certainly can, as long as you keep in mind the current limitations of the micro. Double check with Ohm's law, and the data sheets. Are the LED's turning on at the same time? What about a resistor network IC? One example I can think of is using one current limiting resistor for a couple leds, but the resistor is between ground and the leds. In my example, only one led is on at a time. Not the safest way to do things, but it will work. Proceed with caution.

[CocaColaKid]

I've done this without problems. Just make sure you don't overdrive the I/O. The other thing is that if only one LED is on there shouldn't be a problem. However if more than one is on then the LEDs will dim when you start turning more of them on.

[saturnX]

thanks for the suggestions. the led that i bought is not the normal red ones. its the one that has two colors (red and blue) and it alternates flashes when power is applied and there is like 12 of them. what do you call these kinds of LED's? i might just play safe and go with a resistor each. My other question is power supply, the leds are going into this gift box and at first i was thinking of using watch batteries. How long do you reckon it would last? the LED's won't be on all the time except when its turned on. would this be a better choice of power supply or using AAA batteries. Remember space is limited.

oh ya can some one recommend a particular IC that i could use for this project. I'm still quite new to PIC's and have only used 16f84 chips for my recent projects. will post up my schematics later on for everyone to check.

[CocaColaKid]

I believe these type of leds are referred to as bi-color. Just be sure to limit the current to around 20mA max per I/O.

If the choice is between the AAA and watch batteries go with the AAA. They should provide more power thereby increasing your running time.

I would get away from the 16F84 and look at the 16F628A or 16F648A. There chips are cheaper, have at least double the capacity and I believe they even have an internal oscillator so you can use those extra I/O pins for some other function.

[saturnX]

@CocaColaKid: Thanks for the reply. Yeah i was thinking of AAA batteries as well. Not only that the watch batteries cost a bit as well plus getting the holders for it ain't easy. I will sit down this weekend and draw out the schematics and upload it here soon for you guys to check it out. Considering the IC's you mentioned only prob is that my programmer needs a ZIF adapter to program that particular chip. Have already sourced it out from MeLabs so shouldn't be a problem.