Hey,
I’m trying to get a TLC5940 working with an Arduino but I’m running into some weird issues and I’m not sure what I’m missing.
Power:
9V battery → Arduino VIN
Battery GND → Arduino GND
Arduino 5V → TLC5940 VCC
Arduino GND → TLC5940 GND
Pins:
Pin 11 → SIN
Pin 13 → SCLK
Pin 10 → XLAT
Pin 9 → BLANK
Pin 3 → GSCLK
IREF:
LEDs (just testing with 2):
5V → 180Ω → LED → OUT0
5V → 180Ω → LED → OUT1
(long leg to 5V, short leg to the TLC outputs)
Capacitor:
One 100µF electrolytic between 5V (+) and GND (–)
I don’t have a 0.1µF ceramic capacitor right now.
Just using the basic TLC library and setting everything to max:
#include "Tlc5940.h"
void setup() {
Tlc.init();
}
void loop() {
for (int i = 0; i < 16; i++) {
Tlc.set(i, 4095);
}
Tlc.update();
delay(10);
}
Sometimes the LEDs turn on, sometimes they don’t
When they do turn on, they go off again after about 4 seconds
It’s really inconsistent, like it randomly works
I don’t have the small 0.1µF cap near the chip — could that cause this?
I’m powering it from a 9V battery — is that too weak?
Is 10kΩ on IREF okay or too high?
Does my LED wiring look correct for this chip?
Any ideas what I should check or fix?
jim-p
April 22, 2026, 9:53am
3
gabrielhellow:
I’m powering it from a 9V battery — is that too weak?
If it's not brand new
Is 10kΩ on IREF okay or too high?
To high, try 2K
Does my LED wiring look correct for this chip?
NO. You do not need the 180 ohm resistors
I think you have BLANK and XLAT swaped.
ill try to remove the 1800 ohm resistors im not sure if i have a 2k ohm resistor i do have 1k ohm which i can connect in series. Also im not sure if its okay or not but is it okay to use the 100µF. I want at least 21 green leds connected to 4 of these tlc5940.
jim-p
April 22, 2026, 1:15pm
5
I actually changed it to 3.3K but for testing anything between 2K and 5K will be OK. The larger the resistor the dimmer the LED.
You should have one 0.1uF capacitor for each TLC5940.
For 21 LEDs you will need a separate 5V power supply for the LEDs , do not use the Arduino 5V output.
So the 100uF will not work right?
Is the 0,1uF required for it to work because it looks like the led turns on but dimmed and like turns a bit off etc like it looks like it isnt getting sufficient power + it sometimes turns on and does nothing
I think you completely missed the replys to this statement.
It is not capable of providing the current required to drive your project.
Do you have a DMM? Digital MultiMeter?
What model Arduino are you using?
Tom....
gabrielhellow:
Pins:
Pin 11 → SIN
Pin 13 → SCLK
Pin 10 → XLAT
Pin 9 → BLANK
Pin 3 → GSCLK
Basic Pin setup:
------------ ---u----
ARDUINO 13|-> SCLK (pin 25) OUT1 |1 28| OUT channel 0
12| OUT2 |2 27|-> GND (VPRG)
11|-> SIN (pin 26) OUT3 |3 26|-> SIN (pin 11)
10|-> BLANK (pin 23) OUT4 |4 25|-> SCLK (pin 13)
9|-> XLAT (pin 24) . |5 24|-> XLAT (pin 9)
8| . |6 23|-> BLANK (pin 10)
7| . |7 22|-> GND
6| . |8 21|-> VCC (+5V)
5| . |9 20|-> 2K Resistor -> GND
4| . |10 19|-> +5V (DCPRG)
3|-> GSCLK (pin 18) . |11 18|-> GSCLK (pin 3)
2| . |12 17|-> SOUT
1| . |13 16|-> XERR
0| OUT14|14 15| OUT channel 15
------------ --------
Look at the difference between your wiring for BLANK and XLAT and the wiring in the code example.
i have a 9v energizer battery where i use a buck down converter to make it into a 5v also i do have a multimeter yes
i did try to the the wiring from the example but i can try again to see if i did anything wrong
Do you see the difference between your wiring and the correct way from the example? You have reversed BLANK and XLAT.
also its a arduino mega im using
i copied the setup completly and it still doesnt turn on or nothing in the picture you can see my setup. The 9v battery should be fine for powering 1 led no?
am i missing something?
I can't tell anything from that picture.
Does D10 go to pin 23?
im sorry for the bad picture yes the D10 goes to the pin 23 (BLANK) and the D9 to pin 24 (XLAT)
I can't tell if it wired correctly from your pictures.
Sorry, I give up.
i can try to wire it better up tomorrow and send a better picture
xfpd
April 22, 2026, 10:03pm
20
Wiring in a picture:
A basic sketch, with wiring instructions.
