Reef-Pi Moon Light Help

[diver22]

Hi all, @Michael Lane I have 6 x 3.5v leds in a string. these are the leds , "LED, QuasarBrite, White, Through Hole, T-1 3/4 (5mm), 20 mA, 3.5 V, 2300 mcd" and want to use them as a moon light with the reef-pi PWM, what would I need to connect them to the reef-pi ? or how and what would he need to create the circuit.

I have attached the spec's for the LED Document for further info further info is needed..

Thanks for any help he can get.

 

[Ranjib]

I would start with a 12v power supply, use an lm2596 to power pi . 12v source will also power the leds. Use an npn transistor to control the power of leds with pwm generated from pi.
this videos shows how to setup the circuit for multiple leds. it will help deduce the values of resistors based on how you want to control it.



Pi will provide two pwm pins. I'll recommend starting with a single pwm /npn transistor (2n2222) , a 560ohm resistor (assuming 3.5v drop, 30ma leds, 3 in a series, 12v input voltage ( 12 - 3 * 3.5 = 1.5 , 1.5/0.03 = 500,,, closest common is 560ohm)

 

[diver22]

I would start with a 12v power supply, use an lm2596 to power pi . 12v source will also power the leds. Use an npn transistor to control the power of leds with pwm generated from pi.
this videos shows how to setup the circuit for multiple leds. it will help deduce the values of resistors based on how you want to control it.



Pi will provide two pwm pins. I'll recommend starting with a single pwm /npn transistor (2n2222) , a 560ohm resistor (assuming 3.5v drop, 30ma leds, 3 in a series, 12v input voltage ( 12 - 3 * 3.5 = 1.5 , 1.5/0.03 = 500,,, closest common is 560ohm)

Ok, first Thank you so much for the information you provided, I'm not to certian how to tie in the LM2596 to my PI, so I did some research regarding some parts you recommended and came across some other that make up this, due to my limited knowledge of electronics but my curiosity it pushes me to learn more... lol.

I drew up this, the Mofets board I got from @Tom Bishop with his rig of moon light... would my wire config work. or how Far I'm I from the whole thing...

Thank you! Sorry I'm a picture person...

 

[Ranjib]

Ok, first Thank you so much for the information you provided, I'm not to certian how to tie in the LM2596 to my PI, so I did some research regarding some parts you recommended and came across some other that make up this, due to my limited knowledge of electronics but my curiosity it pushes me to learn more... lol.

I drew up this, the Mofets board I got from @Tom Bishop with his rig of moon light... would my wire config work. or how Far I'm I from the whole thing...

Thank you! Sorry I'm a picture person...

Yes it should work as well. Just check gpio18 and 19 is pwm, not 12, by default. You don’t need a power mosfet , like the one you mentioned , because the current draw is not that high (60ma) which any common npn transistor will do

 

[diver22]

Yes it should work as well. Just check gpio18 and 19 is pwm, not 12, by default. You don’t need a power mosfet , like the one you mentioned , because the current draw is not that high (60ma) which any common npn transistor will do

Ok perfect I will check the PWM pin ... I removed the Power to the mosfet, updated the drawing would this work ? the ground from the Power supply to the Mosfet is still needed corrrect ? if not where does it go to ?

Thank you.

 

[Ranjib]

No you need the power line comibg from PSU to mosfet circuit not directly to the led, if I recall correctly,

 

[diver22]

No you need the power line comibg from PSU to mosfet circuit not directly to the led, if I recall

What do I used to power the led ? Where do I pull the 12 v to the led to reduce it with the 560ohm resister ?

 

[diver22]

Also another question tha came up when buying the 560ohm resister, they have different w 1/4w, 1/2w etc... which one would I need or can I use either one for this ?

 

[Ranjib]

1/4w should be plenty