hey guys, new to the forum, and electronics, and arduino! i dont really have much electronics knowledge, but im quite handy with programming. what i have done is created a program to control all my vivariums with thermostats (already done) and a sunrise sunset which outputs on one of the pwm pins. This works fine, and has done for a few weeks now, (i just have one led connected to output pin). now what i need is to be able to run multiple leds off the pwm pin, i bought some of these http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=380428224415 which is a
High Power 3W 800mA LED Lighting DC Driver, i bought 4 thinking i could use them for normal leds? or should i just scrap them and go the transistor route. i was hoping to use 20 leds in each vivarium (4), if you recomend the tranistor route, any chance of a for dummies guide! cheers
Multiple LEDs all doing the same thing? Or different things?
thanks for the reply. they will all be doing the same thing (a sunrise, stay on for 10 hours, then sunset), sorry i forgot to state. thanks!
Can you describe the LEDs that you are driving (voltage / amperage specs)?
i was going to use a 5volt power supply with 20 LEDs in parallel (3.2v forward voltage, 20ma) with 100ohm resistors. with the driver (im using them as they have pwm controll) is a constant 800ma current, does that mean id have to run 40 off each one to use all the 800ma or would the resistors take care of it, or is it a case of they are designed for high power LEDs and thats it. sorry if its easy stuff, minds just boggling at the moment. thanks
That LED driver would not be appropriate in this case. It's designed for single, 3W LEDs where using resistors would dissipate too much power as heat.
For your situation, you'd use the LED Wizard to calculate how to wire up your LEDs. Preferably you'd use a higher voltage source, such as directly from the power adapter you're using to power the Arduino, to drive the LEDs so you can put more LEDs in series. To switch this power you'd use a simple transistor circuit.
ok thanks very much, would a bc547 or bc548 be suitable for this? and any idea of what size resistor would be suitable at the base? cheers!