I want to control 50+ LEDs, not individually but only using some sort of transistor(s) to make LEDs on at specific time and then make them off.
I'm interested in electronics: What kind of wall adapter i'd need to have enough supply for LEDs (assuming that each one consumes 20 ma). Also what kind of schematic is better, use 1 transistor which handles higher current or just little ones with lower current ?
And all this transistors must be driven using arduino. Project is very easy but i don't want to burn LEDs, or make something wrong.
Fungus omitted to ask more specifically - what colour are these LEDs?
The voltage drop of red LEDs is about 2V, whilst for blue and white it is more like 3.7. So if you have ten red LEDs in series, you will require at least 20V plus a few more for the current regulator circuit, while for ten blue or white, more like 40V.
Note that you do need a current driver to control the current for each series chain, the neatest circuit being this one:
if i use this kind of schematic and control 10 transistors using arduino to power up 50 leds, Does this would be normal ? I'm also interested in whether 12 volt 2A power supply is enough for arduino plus LEDs?
if i use this kind of schematic and control 10 transistors using arduino to power up 50 leds, Does this would be normal ? I'm also interested in whether 12 volt 2A power supply is enough for arduino plus LEDs?
it won't work :
1- the Leds you'll buy are pre-wired with a series resistor, for a 12V power supply - Thus you can't put 10 of them in series with a 12V power supply
2- with a npn transistor, you must put the load (here, the led and included resistor) between +Vcc and Collector, and emitter to 0v . Don't forget to put a resistor between the arduino output and the base !! Search this forum (or google) with the words "arduino, transistor, switch" and you'll find a lot of examples .
3 - you should check the included resistor value, it will tell you how much current each led needs .
your circuit shows a NPN on the high side. need to change that to either an PNP or put it on the low side.
not very efficient as you need to provide a lot of amps at 12V.
most of the power for this project is used to heat the resistors.
you could use twice as many blues, in series if you selected the resistor.
or 4 times as many red, if you selected the resistor.
but it will work.
need to make sure your power supply can handles all the LED's on at the same time and size your transistor for the correct load. may be better off using an FET.
giorgi111-111:
Ok, I know that there are no resistors included, so I'll get BC547 and connect 5 LEDs in parallel and one resistor in series. this would work, I think
We will presume that the resistor which is included with each LED corresponds to 20 mA current draw at 12V - though you should measure this with your multimeter to verify (and if you do not have a multimeter, you should not be working with any electronics ) - so five in parallel will be 100 mA and easily controlled with a BC547 on the ground side of the group of five LEDs.
If by "one resistor in series" you mean a 1k resistor in series with the base of the transistor as it is fed from the Arduino pin, then that is OK.
I can see that the LEDs with pre-wired leads would be a very convenient form to assemble into a display. Most of us observing are thinking that this is an inefficient way to do it but if (and it does need checking) they draw 20 mA each, then the total draw of 1 Amp should be able to be handled by a switchmode "Plug Pack" 12V power supply of 1 Amp rating.
) - so five in parallel will be 100 mA and easily controlled with a BC547 on the ground side of the group of five LEDs.