Hi, i would like to build a control board for an 8x8 rgb led matrix.
I want use the TCL5947 that is a 24 PWM sink current whit a serial daisy chain interface for drive it.
This chip is not o cheap... const around 3$ and i need 8 for driving the whole matrix so i'm thinking on multiplexing it, so using only 1 for controll the 24 row and a 8 bit multiplexer for the col... but is this possible? i mean could be any "interference" between the refresh rate of the multiplexer and the PWM freq? :o
It's not quite the same, because the TLC5947 has a ~4MHz internal oscillator instead of an external grayscale clock. This translates to about 976 updates per second. However, pulsing the BLANK line will reset the PWM timers. If you pulse the BLANK line approximately every ten PWM periods, then move to the next row, you will still end up with about 100Hz refresh rate of the entire array, and the PWM timers will be almost in sync. There will be error at the beginning and end of the timing cycle, but if it's only a few percent of one of ten periods, it may not be noticeable.
The main problem you will have: the TLC5947 is only capable of 30mA on each output. This means you cannot drive the LEDs with larger pulse currents to regain the brightness you will lose with the multiplexing method.
Grumpy_Mike thanks for the suggestion, ery usefull.
macegr
The main problem you will have: the TLC5947 is only capable of 30mA on each output. This means you cannot drive the LEDs with larger pulse currents to regain the brightness you will lose with the multiplexing method.
yes, i know this was also my guess, at the end i'll have to pump up the current to obtain the full led luminosity.
TLC5947 is good if you use 3 OUT for each RGB led directly without mux the signals but on TI site i read
APPLICATIONS
Static LED Displays
Message Boards
Amusement Illumination
TV Backlighting
I don't understand why "static LED display" the Data Clock is 15Mhz so where is the limitation, instead the 594 0, 1, 2, 3, 4, 5, 6 report
As soon as you latch the data into the PWM registers, they turn off until the next cycle. Maybe this would provide too much flickering in a full motion video display. They also have internal oscillators so it would be difficult to sync frames, though it makes it easier to interface.
i'm evaluating to use 1 5940 that is 16ch PWM at 150mA to drive a 4x4 RGB matrix.
My intention is to use 12 ch to drive the 4 row and the other 4 ch to drive 4 FET that connect the LED to the 5V.
So to update a compete matrix i have to send 4 data set to 5940 waiting for 4096 pwm pulse x 4 (maybe i can interrupt earlier the pwm count using the BLANK but loosing in color resolution, any way supposing 4096 clk pulse x 4 divided for clk freq i can obtain the max update rate for 1 matrix, tha problem is, ho fast can be the arduino pin used for clock?