LED Lighting Project

Thread Starter

Andrei Moldovan

Joined Jul 26, 2016
8
Hello Everyone,
I am working on a LED lighting project which is beginning to be a hassle. My goal is to control the flashing of 45 LED's connected in groups of 5 with a PicAxe 14M2 project board. My initial attempt was only temporarily successful as my LED's are now fading.

Components are as follows
12 V rechargable battery
9 2N2222A NPN transistors (function as switches controlled by the 14M2)
9 120 OHM Resistors (Functioning as current limiting resistors)
45 white LED's set into 9 groups of 5 LED's
9 330 OHM resistors between the PicAxe pins and the transistor gates

My guess as to why it is failing now would be the setup of the LED's In each of the 9 groups LED 1 and 2 are in parallel with each other and series with LED 3 and 4 which are also in parallel with each other, and LED 5 is in series with the negative leg of LED 3 and 4.

If anyone has any tips or might think they know a solution please comment, looking forward to the varied views of my problem.

Regards Andrei.
 

tracecom

Joined Apr 16, 2010
3,944
My guess as to why it is failing now would be the setup of the LED's In each of the 9 groups LED 1 and 2 are in parallel with each other and series with LED 3 and 4 which are also in parallel with each other, and LED 5 is in series with the negative leg of LED 3 and 4.
Probably. It is never a good idea to parallel LEDs and use a single current limiting resistor. With white LEDs and a 12V power source, you are limited to running 3 LEDs in series and a 62 ohm resistor (assuming the LEDs are 20mA devices.) You can run the other 2 in the group of 5 in series with a 240 ohm resistor. Resistors and 2N2222A transistors are cheap.

I hope you aren't running the PICAXE on 12 volts? It won't last long.
 

Thread Starter

Andrei Moldovan

Joined Jul 26, 2016
8
Sorry for the LONG delay, and thank you for the input. I will upload a schematic shortly. i made a few changes and will also include those in the next post.
 

Thread Starter

Andrei Moldovan

Joined Jul 26, 2016
8
Update.
I now have 2 12 V Batteries in series for 24 V. So now i can power 5 LED's in series.

The PicAxe microcontroller has its own power supply for 4.5 V.

Purchased the LED's on amazon and VERY little data. they are 3.2-3.4 Vfw. and 10000 - 12000 Lumens MCD

Problem #1. using a transistor as a switch. I purchased them off amazon, and the datasheets are nonexistent. how would i figure out what resistor i would need to go to full saturation for minimal voltage drop across CE? is it alright to "floor it" on the base current since I am limiting the current before it reaches the transistor?

I hope the picture is clear. if there are any questions or things i should include for a better answer ask away. i will be more punctual with my replies.

20160811_194408.jpg
 

tracecom

Joined Apr 16, 2010
3,944
You may need to do some destructive testing on at least one of the LEDs to find out how much current it will draw before burning out.
 

bertz

Joined Nov 11, 2013
327
Update.
I now have 2 12 V Batteries in series for 24 V. So now i can power 5 LED's in series.

The PicAxe microcontroller has its own power supply for 4.5 V.

Purchased the LED's on amazon and VERY little data. they are 3.2-3.4 Vfw. and 10000 - 12000 Lumens MCD

Problem #1. using a transistor as a switch. I purchased them off amazon, and the datasheets are nonexistent. how would i figure out what resistor i would need to go to full saturation for minimal voltage drop across CE? is it alright to "floor it" on the base current since I am limiting the current before it reaches the transistor?

I hope the picture is clear. if there are any questions or things i should include for a better answer ask away. i will be more punctual with my replies.

View attachment 110370
Since you are using a 24 volt supply, why are you limiting yourself to only 5 LEDs in each string? You should be running at least 6 LEDs in each string and using a 220 ohm current limiting resistor in each string. Then you only need 8 output pins.
Use a 1k resistor between each output pin of the 14M2 and the base of each transistor, you'll have more than enough current to turn the transistors on and off.
General purpose LEDs are typically rated at 20 mA with a not to exceed of 30mA. Running them over 20 mA will greatly shorten the life of the LED.
 

Thread Starter

Andrei Moldovan

Joined Jul 26, 2016
8
hey guys, here is the link to the LED's and transistors i am using.
LED https://www.amazon.com/dp/B0087ZT06U/ref=nav_timeline_asin?_encoding=UTF8&psc=1
Transistor https://www.amazon.com/2N2222-Plastic-Encapsulate-Power-Transistors-600mA/dp/B00R1M3DA4
I am content with using 5 LED's as it is a prototype. any changes can be made after the project has been made to work properly.
i have been tinkering with this stupid thing for a long time and my transistors are refusing to switch on and off. i have tried dozens of the i purchased and they are all being stubborn. they are functioning properly when i test them.

i am so frustrated i want to scrap the whole thing and call it a day, but i will never get better at this if i do that. so please any help would be welcomed.
 

hp1729

Joined Nov 23, 2015
2,304
hey guys, here is the link to the LED's and transistors i am using.
LED https://www.amazon.com/dp/B0087ZT06U/ref=nav_timeline_asin?_encoding=UTF8&psc=1
Transistor https://www.amazon.com/2N2222-Plastic-Encapsulate-Power-Transistors-600mA/dp/B00R1M3DA4
I am content with using 5 LED's as it is a prototype. any changes can be made after the project has been made to work properly.
i have been tinkering with this stupid thing for a long time and my transistors are refusing to switch on and off. i have tried dozens of the i purchased and they are all being stubborn. they are functioning properly when i test them.

i am so frustrated i want to scrap the whole thing and call it a day, but i will never get better at this if i do that. so please any help would be welcomed.
I couldn't find a data sheet for your LED. From vague guess I would say it is rated for 20 mA. I don't know how reliable it might be at 30 mA. Bargain price, huh?
Have you considered edge lighting of a panel instead of the rows and columns of LEDs? Such as used on LCD screens.
 

Bernard

Joined Aug 7, 2008
5,283
Looks like 10000mC = about 20ma. 5 LED's, on 24 V needs about 390 ohms ti series. @ 20 mA output, 2N2222 needs about 2 mA input, If 4 V drive available, then 2k ohms about right for base R.
 

Thread Starter

Andrei Moldovan

Joined Jul 26, 2016
8
I couldn't find a data sheet for your LED. From vague guess I would say it is rated for 20 mA. I don't know how reliable it might be at 30 mA. Bargain price, huh?
Have you considered edge lighting of a panel instead of the rows and columns of LEDs? Such as used on LCD screens.
I am not sure what that is, or how to implement it. since i am already so far into this prototype i will try and finish it with the transistor and series leds, but i am interested in possible using it on version 2.0 would you mind dropping some info about the edge lighting panel?
 

Thread Starter

Andrei Moldovan

Joined Jul 26, 2016
8
Looks like 10000mC = about 20ma. 5 LED's, on 24 V needs about 390 ohms ti series. @ 20 mA output, 2N2222 needs about 2 mA input, If 4 V drive available, then 2k ohms about right for base R.
Hey Bernard, thanks for the suggestion, i will go out and buy the resistors I need and see if i can get the dang thing to work. hopefully its everything works out and i can be done with this shenanigans.
 

hp1729

Joined Nov 23, 2015
2,304
I am not sure what that is, or how to implement it. since i am already so far into this prototype i will try and finish it with the transistor and series leds, but i am interested in possible using it on version 2.0 would you mind dropping some info about the edge lighting panel?
instead of lighting a panel from behind with rows and columns or LEDs just light it from the edges, like your LCD monitor does.
 
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