No full brightness on Tlc5940 ?

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi, im having problems controlling full brightness with a tlc540 using the latest library from Google Code Archive - Long-term storage for Google Code Project Hosting. using the suggested hardware setup on the playground Arduino Playground - TLC5940

I'm using Orange 5mm water clear 12000mcd leds. 28mah 2.6v

Even when using Tlc.set(channel, 4095) the leds are a lot dimmed when compared to a regular setup using 5v and a resistor...

Am i missing something ? :-[

Thanks

2

What value of current controlling resistor are you using on the TLC5940?
What value of resistor were you using with the 5V setup?

Do these provide the same current through the LED?

When you say 28mah do you mean 28mA because mah is a rating you would give a battery.

3

Hi, im using the 2k and 10k resistors as suggested on http://students.washington.edu/acleone/codes/tlc5940arduino/img/breadboard-arduino-tlc5940.png

the led is 28mA ..

4

So a 2K current resistor on the TLC5940 will give 20mA. What I was asking is how does this compare to the current through the LED when you are connecting it to 5V through a resistor. So what size is that resistor?

I calculate it should be about 85R if you power it from 5V.

To get 28mA through the TLC5940 you need a resistor of 1.4K.

Then they should be the same brightness.