24channel 12bit SPI pwm/leddriver on the raspberry pi

EL Wire/Tape/Panels, LEDs, pixels and strips, LCDs and TFTs, etc products from Adafruit

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
fjw
 
Posts: 1
Joined: Wed Aug 14, 2013 1:30 pm

24channel 12bit SPI pwm/leddriver on the raspberry pi

Post by fjw »

Hi,

last week I bought the 24channel 12bit SPI pwm/led driver at your store.

I wrote a node.js SPI library https://github.com/fjw/node-simplespi
and a library especially for this led driver https://github.com/fjw/node-leddriver
and everything works fine.

But I am still curious and a little bit unsure about the wiring.

So here my questions:

Is it correct to wire CE0 of the raspi to LAT (input side) on the driver? It also works without this.
Is it correct to connect /OE (input side) to ground? In the documentation it says i can turn off all LEDs by dropping this. But instead all LEDs turn off if i set it to HIGH. I am not sure if this is intended or an error...

Most important question:
Is it really safe to connect V+ (input side) to 5V if my raspi logic goes by 3.3V? What is the other 5V pin (on the base of the transistor) for?

Thanks and greetings from Munich
Frederic

User avatar
adafruit_support_rick
 
Posts: 35092
Joined: Tue Mar 15, 2011 11:42 am

Re: 24channel 12bit SPI pwm/leddriver on the raspberry pi

Post by adafruit_support_rick »

Frederic-
fjw wrote:Most important question:
Is it really safe to connect V+ (input side) to 5V if my raspi logic goes by 3.3V? What is the other 5V pin (on the base of the transistor) for?
All the signals are output signals, so the pi will be generating a 3.3V logic level. These lines will never see 5V levels.
fjw wrote:Is it correct to connect /OE (input side) to ground? In the documentation it says i can turn off all LEDs by dropping this. But instead all LEDs turn off if i set it to HIGH. I am not sure if this is intended or an error...
We'll have to fix the product page where it says that. "OE" stands for "Output Enable". The '/' before "OE" means that the logic is inverted; i.e., the signal is active LOW. So the outputs are enabled when /OE is low, and disabled when /OE is high, just as you discovered.

The rising edge of LAT moves the data from the shift register into the data latch (i.e., PWM register). I'm not sure why it would work without connecting LAT to anything. What should happen is that you send all your data, and then toggle LAT low-high to display the data.

Locked
Please be positive and constructive with your questions and comments.

Return to “Glowy things (LCD, LED, TFT, EL) purchased at Adafruit”