Hello everyone, i have a little project that i have been working on and i wanted to see if the arduino could be used on it.
i made a stip of led and the total voltage comes up to 560mA and the leds run at 3.3v
my question it, the max mA the arduino pushes out is 40mA correct, is there something i can use that the arduino could still safely pulse these lights on and off as many time as id want?
i think a npn ?? someone once told me, but how would i connect that with the arduino?
You need a seriuos transistor driver, or a couple of darlington arrays like the ULN2003.
You also need an external powersupply, as you can not draw 560mA from Arduinos powersupply.
total voltage comes up to 560mA
No the total current is 560mA, it might not seem important to use the right word but it is. The voltage is 3.3V or 3V3 as we say.
For a power supply see:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html
Look at this:-
http://www.thebox.myzen.co.uk/Workshop/Motors_1.html
and
http://www.thebox.myzen.co.uk/Workshop/Motors_2.htm
For turning them on and off.
Motors and relays and LEDs are very similar when it comes to switching them.
great !! nice info,basially what im going to do (please bare with my) is make some cop lights from very bright 20mA led,
i want to set everything up so that all i would have to do is when the day i want to use these lights for car show or what ever is i would have to bring my arduino chip n just place all the pins that i would lable and its good to go, so basically thwe arduino would b the brain and i can remove and reprogram for other projects,how does that sound??
okay now, reading the links u provided (thanks alot btw,great info) since it is for the my car i can just apply npns to control the excessive volts and since its a car batter,there enough juice to go around for the arduino and the lights and i can set up in pic 3 from the first link u posted right ?? (pretty cool when u understand stuff huh)
Yes that looks fine.
Best of luck.
Thanks man, could i apply direct 12-14v from a car battery to the arduino chip?? or would i have to knock down the voltage to 9.6 by using resistors or something like that ??
thanks again so far for the help 
12V is ok but a car batterie usually goes in the 13.8V.
You could add 1 or 2 Diode in serie to drop the voltage by 0.7-1.4V, and everithing would be just nice.
K according to your diagram you have a total current of 70mA and a voltage drop of 9.9V (3.3 * 3).
So you need a supply greater than 10V and 70mA.
The resistor in series with the LEDs limits the current. So if the high side of your supply is 13.8V using Ohm's law you get 13.8/.07 = 197 ohms
You could add the diodes but I don't know why dropping down the voltage is neccessary in this case (I've been wrong before though... very wrong...). Just figure out the average value of the battery (assuming the variation is small) and use that to calculate the resistor.
If the variance is big, your LEDS are going to glow. If you want to make the light steady you are going to need a few decoupling caps and maybe a regulator.
Please do not use a series resistor to drop the current, the regulation problems you will get are just horrid. Use something like a series regulator down to 9V first an spread that heat dissipation.
I understand the use of a regulator, but isn't that because he is using a battery and the voltage decreases?
Wouldn't power dissipitation depend on how many amps the battery is being spit out by the battery as well? Suppose he had a regulated 12V supply that was pushing .1A of current, wouldn't a 3W resistor be fine for power dissipitation?
Am I missing something obvious here? (It has happened before...)
okay cool, check this one out, would work better
and also i still would need a little resistor after the regulator towards the led, iv seen that if i dont the leds dont normally last there life span but i think this set up (thanks to everyone thats helping me) will work alot better but one question,
where would i get a 9.6v regulator?? radioshack dont carry them and i cant really find them online, any good store that u guys buy from ??
and also my main part in this project is to get the arduino to be able to pmw the led's i still have to learn the coding to make the strobe effect, and make inputs (because i was 5 bottons, 1 to turn off the system and the other 4 to make 4 diff strobe patter) but thats another game itself
I'd use 10V voltage regulators. you need 9.9 for 3 LEDS and your collector needs to be a bit higher than your emitter for you transistor to work.
Check digikey for the regulators.
thanks for the advice, but i can still used the 9.6 reg for the arduino chip right? or i should also up that to 10v??
and thanks for the site,will check them out, do you by any chance have any other site besides digikey ??
couldn't you just use some constant current setup ?
like: 12V
|
LEDS
|
|/
Ard.----1k----|------| (NPN)
| |
| |
(NPN) |------|
/| |
| R2
| |
| |
GND GND
I(leds) ~ 0.7V/R2
If the voltage drop on the leds is 9.6V and the car battery has say 13.8V at worst, the transistor will take the difference and be heated with less than 1/2 Watt (at 70mA).
