Hello
A simple question. How can I measure the pwm frequency of a TLC5940 Output? I tried with a Multimeter but couldn't measure anything. On arduino mega pwm Output it works with connecting one to ground and the other to pwm Output Pin. There I get a frequency of about 500 Hz.
How Do I have to connect the Multimeter to the TLC5940?
I don't know why you think a multimeter would do this. Maybe some fancy one I have never seen.
Normally people will get some kind of oscilloscope for this.
For a 5940, have you read the datasheet ? Why do you actually need to know ?
Because I have read some multimeter which can measure frequencys also can Do this. Why Not. I don't have an oscilloscope. Of course then it would be easier.
I want to configure the TLC5940 library to get an Output of min 20 KHz and no one can tell me how to Do this. So I have to find it out myself
When I use for example pin 7 on the arduino mega board for controlling a fan I can measure a frequency of 490Hz with a multimeter so I think it works well. But why doesn't work with the output of the TLC5940? Where do I have to connect the probe tips of the multimeter?
You won't see anything at the outputs without a pull-up resistor, is a current sink driver.
There is a pull-up resistor. sorry I forgot to say.
But I think it is another problem maybe something is broken I try to find out at the moment...
But with the pull-up resistor it should work doesn't it?
If its in the range the multimeter can handle, yes. Multimeters don't normally do high frequencies, thats where you stick a 'scope probe on the circuit to see what's happening.
Read the datasheet of the 5940. It has two clock signals. One controls the SPI communications and the other one controls the PWM output to the LEDs.
I was reading instructions for driving this from arduino a few weeks ago, I can't find it now, but the instruction was to drive the PWM signal from the arduino using some method I didn't quite understand, to get the arduino clock speed to be output on one of the pins which is connected to the pwm clock input of the 5940.
If you google "5940 GCLK", there are a lot of examples of how this is done.
MaikB85:
I want to configure the TLC5940 library to get an Output of min 20 KHz and no one can tell me how to Do this.
Rubbish. Lots of people can (including me).
Have you even looked at "tlc_config.h"?
fungus:
MaikB85:
I want to configure the TLC5940 library to get an Output of min 20 KHz and no one can tell me how to Do this.Rubbish. Lots of people can (including me).
Have you even looked at "tlc_config.h"?
Of course I looked to the tlc_config.h but couldn't find a solution for configure 20KHz or more. Examples are max. 4 kHz. So can you tell me which values I have to use?
I found out max possible frequency is 31.25KHz with 256 steps but how to configure it?
Well I got it working but not in the way I wanted. Measuring the frequency works good after rebuild my own tlc5940 curcuit (Before I used the sparkfun pwm shield) I think the other shield is damaged or something.
I tried different configurations with tlc_config.h:
#define TLC_GSCLK_PERIOD 1
#define TLC_PWM_PERIOD 512
-> I get a frequency of about 15,62KHz but only can use 256 steps theoretically
#define TLC_GSCLK_PERIOD 1
#define TLC_PWM_PERIOD 256
-> I get a frequency of about 31,25KHz but only can use 128 steps theoretically
128 steps is not much... I think I have to live with a lower frequency. With these settings I could not really turn off the channel and when I use more than 128 steps on 31,25KHz the frequency collapses. Maybe someone find another solution for getting higher frequencys.