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Topic: Problems using shiftOut for SPI LCD (Read 1 time) previous topic - next topic

So I'm trying to hook up this LCD to my Nano.


I've double checked all my connections and everything appears correct. however I can't get it to even turn on. After rechecking my connections I realized that while I have 3.3 going to the power for the chip, all the SPI lines are running at 5V because that's what the Nano runs at. So is it possible I fried my board by doing that? Or is that ok? Here's my code. I based it on a few different examples I've seen, but I feel quite confident that I screwed something up in it. It doesn't even seem like it's turning the board on. I don't know what it would do when it turned on, but I sorta feel like I'd see SOMETHING happen, even if it wasn't printing the data properly to the display.

Code: [Select]
#define RE 17
#define CS 6
#define SC 7
#define SI 8
int serialcounter = 1;
#define RS 5

void setup()
//initialize the LCD
  pinMode(RE, OUTPUT);
  pinMode(RS, OUTPUT);
  pinMode(CS, OUTPUT);
  pinMode(SC, OUTPUT);
  pinMode(SI, OUTPUT);

  digitalWrite(CS, HIGH);
  digitalWrite(RS, HIGH);


void initLCD(){
  digitalWrite(RS, LOW);
  digitalWrite(CS, LOW);
  spi_transfer(B00110000); //wake up
  spi_transfer(B00110000); //wake up
  spi_transfer(B00111001); //function set
  spi_transfer(B00010100); //internal osc frequency
  spi_transfer(B01010110); //power control
  spi_transfer(B01101101); //follower control
  spi_transfer(B01110000); //contrast
  spi_transfer(B00001100); //display on
  spi_transfer(B00000110); //entry mode
  spi_transfer(B00000001); //clear
  digitalWrite(CS, HIGH);

void spi_transfer(int data) {
  digitalWrite(CS, LOW);
  digitalWrite(RS, HIGH);
  digitalWrite(CS, HIGH);

void clearDisplay() {

  //clear the display
  spi_transfer(B00000001); //clear


void loop(){
  digitalWrite(13, HIGH);
  digitalWrite(13, LOW);

Well, I just noticed one problem, I'm calling RS HIGH in my spi_transfer function which means all my "command" transfers during init are being transfered as data, which would of course make nothing turn on. I kinda doubt that's the whole problem though, as I just had added that to spi_transfer thinking it would save me calling it out every time I called spi_transfer. I'll just write separate data_transfer() and com_transfer() functions.


You could use http://code.google.com/p/doglcd/. doglcd was written for ST7036, but it should be compatible to your ST7032 based display.


Awesome, I'll give it a shot.

Do you know about the voltage issue? I need to know if I have to order a 3.3V board from somewhere. Thank you for the help!

Also, there isn't a problem with using a output pin to ground a circuit as opposed to power it is there? In otherwords I want to put the pin between the backlight led and ground as opposed to between VCC and the backlight. Thanks!


Well, good question. I never tried to apply 5V inputs to a 3.3V display. Sometimes, the data sheet says that the inputs are 5V tolerant, but i did not find such an information in the ST7032 data sheet. So maybe you could try the display with a valid software to check if the display still works.


It works! You are my hero. :-) I can't tell you how frustrated I was with this silly thing. Note that it does not work unless you set the parameters in doglcd to 3.3V (duh). I kinda doubt having the 5V inputs are good for it, but it didn't kill it. the controller can be run at 5V but I doubt it's good for it to have 3.3V power and 5V inputs. Certainly not a long term solution, but for the moment, the screen is working and this guy is happy. :-)

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