Using a transistor to switch on 9V LEDs?

I've been trying to work this out myself for a while now, but i'm stumped!
Has been far too long since i last did electronics :slight_smile:

I have some 9V LED strips connected to a 9V battery pack. I need a way to turn them on and off with the arduino.

I've tried a few transistors, (i have b bag of random ones from maplins) but it only seems to make the LEDs switch between dim/bright, not on/off

I'm getting the feeling i'm missing something blatantly obvious here, can someone point me in the right direction please?

You do it in exactly the same way as you switch a relay.

But you can miss out the diode as the LEDs aren't an inductive load.

failquail:
I've tried a few transistors, (i have b bag of random ones from maplins) but it only seems to make the LEDs switch between dim/bright, not on/off

I'm getting the feeling i'm missing something blatantly obvious here, can someone point me in the right direction please?

Try telling us exactly what you're doing. Draw a sketch. Photograph it. Post your Arduino code. etc.

Find an NPN transistor - you'll have to researchthe part numbers, look up each one at digikey.com or similar.

Then connect as above; +9 to LED strip +, LED strip - to NPN collector, NPN emitter to Gnd.
220 ohm resistor between arduino pin and NPN base. Should turn on pretty bright.
If not, find an NPN with lower Vce, or use a Logic Level N-channel MOSFET with low Rds (a part with 30, 40 mOhm (milli-ohm) resistance at Vgs = 4.5V)

Thank you all, gives me some clues on things to try :slight_smile:

Also relays... knew i missed something obvious
I'll look up the Logic Level N-channel MOSFET too.

I'll post back with schematics if i'm still stuck