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1  Using Arduino / LEDs and Multiplexing / Re: New to Arduino - TLC5940 questions on: January 29, 2013, 06:53:30 pm
Ah ok! Thanks for clarifying that fungus!

I'll definately be putting a resistor on each LED. says that a 15ohm resistor on each LED will dissipate 216mW per resistor which I guess leaves the TLC hardly anything to dissipate- does that soudn right to you? I thought I'd try and double check this and looked up resistor dissipation on wikipedia and got this equation but it's midnight here and my brain isn't working too well- I'll take another look in the morning.
2  Using Arduino / LEDs and Multiplexing / Re: New to Arduino - TLC5940 questions on: January 29, 2013, 06:19:09 pm
Thanks for the input guys. I went back and started from scratch, ended up attaching the Power Supply's "+" and "-" to the breadboards "+" and "-" lines while leaving the Arduino's +5V and Gnd Plugged into the same lines and its all working.

As for the power dissipation the TLC5940 datasheet say's it has a power dissipation of 2.5W- fungus you stated 1.5W is this just incoraporating a safety margin?

My LED's use 3.2V at 120mA so 5V-3.2V = 1.8V.... 1.8V * 120mA == 0.216W per channel. 2.5W/ 0.216W = 11.57 ..... So I can run 11 of these LED's.

Putting these numbers into this site: -advises that I use a 15ohm resistor on each channel in order to run all 16 of LED's.

Hopefully that will work- I haven't accounted for the current the TLC uses and am new to this so might be completely wrong!
3  Using Arduino / LEDs and Multiplexing / Re: New to Arduino - TLC5940 questions on: January 29, 2013, 12:57:56 pm

Hope it's ok to bring this thread back- thought it's best to keep everything in one place rather than starting a new thread.

I've recieved my LEDs and Power Supply and am trying to follow John's instructions of plugging it all together- already burnt out one TLC5940 so thought I'd be better off posting here!

My power supply is Regulated 5V 2000mA. I've used the following image to set everything up on breadboard:

To do the following:
>> Regulated 5V supply at 2A or more:  Connect + to the Arduino "+5V" pin.  Connect + to the TLC "Vcc" pin.  Connect + to the anode of each LED.  Connect - to Arduino "GND" and TLC "GND".

I've tried leaving everything plugged in as it is and adding the Power Supply's "+" to the "+" line on the breadboard and Power Supply's "-" to the breadboard's "-" line- When I do this nothing works?

I've also tried replacing on the breadboard the wires from Arduino's "+5V" and "GND" and plugging my Power Supply's "+" and "-" into the holes the Arduino's wires were in. Also doesn't work.

Should I plug the Power Supply's "+" directly into the Arduino's Board's +5V Pin? That doesn't seem to make sense as then the power wont be getting to the breadboard?

Just tried plugging the Power Supply's "+" into the Arduino's Vin Pin and the power supplies "-" into the Breadboard's "-" line. This works but I'm aiming to run 16 120mA LEDs fora total of 1920mA- and I've read the Arduino wont let more than 1000mA through it?

Sorry to ask for help for such a simple question I just don't want to mess any more chips up!

4  Using Arduino / LEDs and Multiplexing / Re: New to Arduino - TLC5940 questions on: January 20, 2013, 10:38:47 am
Hi John, thanks for taking the time to help- you've made it a lot clearer.

I'll probably be back once my bits arrive!
5  Using Arduino / LEDs and Multiplexing / Re: New to Arduino - TLC5940 questions on: January 19, 2013, 09:00:11 am
Thanks for your help, still trying to get my head round this.

I've ordered 2 different sets of LED's-
First set has a DC Forward Current of 120mA and DC Forward Voltage Typical-2.4v Max 3.2v
Second set is described as If 20mA, Vf = 3.4v, Vr 5v Max

I take it the second set's Vr refers to the Forward Voltage Max in the first set.

Bearing in mind I'm still at the level of trying to understand circuits as pipes full of water can you let me know if the following is correct.

1.The Ardunio outputs 3.3v or 5v, if plugged in to the USB the max amps is 400mA if plugged in to the mains max amps is 900mA.

2.If I supply the TLC4940 with 5v, it magically converts this up to a maximum of 17v - this bit I can't really fit into my water/pipes/pump understanding of circuits! Do I set how many Volts it outputs through software or does it do this automatically?

3.So the TLC4940 will provide enough Volts for- 5 of my first LED's - 3.2v x 5 = 16v or 3 of my second set of LED's 5v x 3 = 15v.

Then we get to amps.

4.Driving the TLC4940 at 5v will put out up to 120mA per channel. To output at 120mA I use a 0.32K resistor, If I want to use 5 of my first set of LED's I'll have to use the Ardunio's external power as 5x 120mA = 600mA which is bigger than 400mA!

5.To output 20mA I'll use a 1K resistor, and I'll be able to use the Ardunio's USB power as 3 x 20mA = 60mA which is less than 400mA.

This seems bit of a shame as I was hoping to power 16 LED's without resorting to an external power source- I guess I'll have to go down that route?

Following this logic which I really hope is flawed- To drive 16 LED's at 20mA each = 320mA I can use the Ardunio's USB Power as 320mA is less than 400mA however I'd have to use some kind of external power for the LED's which would be 16 x 5v = 80Volts - that seems mad! Please tell me where I've gone wrong! Just to clarify I want each LED on its own channel so they can be faded individually.
6  Using Arduino / LEDs and Multiplexing / New to Arduino - TLC5940 questions on: January 18, 2013, 05:30:58 pm

I new to Arduino- started reading up yesterday and ordered an Arduino this evening. I'm wanting to be able to fade 16 LED'S up and down individually- I understand a TLC5490 will let me do this. I eventually want it to drive high power LED's and so have read about Multiplexing and MOFSET but I want to keep things simple as this is my first project.

I have quite a few questions.

1. I'm not up to speed on amps, watts and volts - but need to buy some LED's. What are the brightest white LED's that the TLC5940 can power when 1 LED is on each of it's channels- without going into Multiplexing or MOFSET or an additional power source. I've read that each channel can output 120mA- does this mean that it can output 16 x 120mA all at once?

2. Does this mean that any LED's which are advertised as being 120mA will work- how does the LED's watts and volts come into the equation.

3. I understand the Arduino outputs 5V does this mean that my circuit will run at 5V? Does this mean that any LED's rated up to 5V are ok?

4. I've read the TLC5940 doesn't need a resistor connected to each LED is this correct?

5. Ive ordered an Arduino, breadboard, wire and a TLC5940- Looking at the "Basic Use Example" of acleone's TLC5940 library it looks like I'll also need a 2k Resistor. Is this correct and are there any other bits I'll need apart from the LED's of course?

Hope someone can help!
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