Instructables

Control a 12v LED strip with a 1v to 3v supply. in an 8 LED chaser project 12v strip has to mimic the same as 3v Leds.?

I have an 8 LED chaser project with a PIC 16F682a at the heart of the project. The Pic is programmed to display programmed patterns and each Led has 4 brightness levels.I found the Led's to restrictive and wanted to use 48cm strip Led lights which require a 12v supply. As the maximum current that the PIC can source from an I/O port pin is 25mA and was intended to drive up to 3v Leds with a 270 ohm limiting resistor. I simply want to replace the 3v Led's with 48cm 12v strip Led's for a larger display. 10 years ago I could have knocked up this circuit in a few minutes but I have trouble remembering anything these days. Any help would be very very much appreciated and hopefully the folk of the indestructibles might find the information very positive when applying this in the future when larger Led arrays are needed. The project would also make a cool disco lighting effect too as it comes with 34 pre programmed effects.
PS: I would like to add a 5 bit PWM signal providing each of the 8 LED channels with four levels of intensity; off, dim, mid, bright. I have looked in a logic level shift but feel very out of touch being away from electronics in pursue of another career. Thanks again Spence

See here for original project. picprojects.org.uk/projects/ledchaserpwm/index.htm

usLEDsupply3 years ago
it is fairly simple you will need one of these PWM/TTL Amps then connect the RGB inputs on the amp to your 2v - 5.5v source (the PIC) and a 12v power supply to the 12v input on the amp then the 12v strip to the RGB output and the 12v strips will change color and brightness based on your 2 volt PWM input:-)

for a wiring diagram checkout Fritzing.org
gmxx4 years ago
 if the led strips need 12v to function, they will probably not light with 3v.

the circuit you need will use some transistors to switch the higher voltage and current. 

pwm is the rapid switching of the on and off signals, and the transistors will work with pwm.
CodfishCatfish (author)  gmxx4 years ago
Hi and thanks for the very swift reply. Up to now I was aware that the Led strips need at least 9v and considered transistors using the 3v (adjusted to transistor) at the base. I am not unfamiliar with PWM signals but wanted to get an exact replication of the 3v signal at a 12v level (hence needing a logic level converter to gap the 3v to 12v). So the PWM would dim the 12v led strips accordingly. I will try transistors but have no idea if the logic of the PWM will be replicated. Thanks again and will go ahead with you advice and will of course keep the Indestructibles informed on my progress.
 no problem. remember, pwm is really just the rapid on and off logic. literally, the lights will turn on and off faster than your eye can perceive, and will appear dimmer or brighter. a pwm signal set at a 50% duty cycle means that the lights will appear approx. half as bright as full power.

you are not going to need any additional circuitry to perform pwm outside from the transistors used to isolate the 12v bars from the micro controller.

if you can code the pic to make the 3v led do whatever brightness you want with pwm, then all you will do is add the transistors to bridge the microcontroller to the lights.

wikipedia has a great article on pwm
CodfishCatfish (author)  gmxx4 years ago
Hi again, after doing some more reading I found that my original idea of using a Jfet was not that far off. I have since found out that a  STP36NF06L Modfet will do the trick. Over here in the UK there quite cheap at £0.28p or approx $0.50 cents USA each.With just a few compopnents I'm quite sure the circuit I have included is the way forward. I can't thank you enough for the reply as I don't think I would have pursued this project. As always will keep this post open to update the instructables informed of the progress and hope that the overall finished product will please those who wish to add spark to there disco lighting without breaking the piggy bank.

picprojects.org.uk/projects/rgb/LEDarraydriver.pdf