Controlling String of 24v LEDs with Arduino

Other Hardware LEDs and Multiplexing
1

I've three sets of 24v LEDs with 40 LEDs in each set and would like to turn them on and off using an Uno. Should I use the transformers through a transistor and switch them with the arduino? If so what type of transistor should I get?

Alternatively I could use something like the RGB LEDs here:

http://oomlout.co.uk/collections/extra-pieces/products/led-pirhana-rgb-x3

...although is it possible to power a number of them in series? I'd like to be able to change the colours as a whole but don't need them to be individually addressable.

Thanks, Beth.

2

24V LEDs? Do you have a link to that?

Type of transistor to use will depend on the current to be controlled. For high current, low voltage loss, a Logic Level, Low Rds, Low Gate Capacitance N-Channel MOSFET is ideal.

Common anode or common cathode RGB LEDs cannot be wired in series, only in parallel.
There are surface mount RGB LEDs that have separate anodes & cathodes (6 pin packages), and these could be wired in series, with a current limit resistor needed per color.

3

I have three sets (R, G and B) of these:

...so was wondering if I wired them up to switch through a relay or MOSFET or something, could I turn them on and off?

Alternatively making a string of RGB LEDs (in parallel) is a possibility but I'm not sure how many I could drive from the Arduino.

Thanks!

4

Yes you could. But a Relay would be no good for fading.

For advice on transistors, you need to measure the voltage the transformer gives under load and with no load. Also measure the current under load.

Paul

5

betandr:
I have three sets (R, G and B) of these:

http://www.lights4fun.co.uk/i/q/SLF-40-B/40-blue-led-indoor-fairy-lights-on-clear-cable

...so was wondering if I wired them up to switch through a relay or MOSFET or something, could I turn them on and off?

There should be a label on the transformer.
What is the voltage and current ratings for the transformer?
That should give you a good idea of what you will need.

6

ieee488:
There should be a label on the transformer.
What is the voltage and current ratings for the transformer?
That should give you a good idea of what you will need.

Hmm.. I've found they are often vague, and don't even indicate if the voltage is regulated or not. Better to measure!

7

PaulRB:
Hmm.. I've found they are often vague, and don't even indicate if the voltage is regulated or not. Better to measure!

They call it a "transformer".
I am thinking it is a AC/DC adapter.

8

In the end I used a relay shield:

https://www.coolcomponents.co.uk/relay-shield-v2-0.html

...which works really nicely. I've wired the lights through the NO and can control them with the Arduino's digital out. Thanks for all your help! :slight_smile: