The proposals in the GxEPD2_MultiDisplayExample.ino example in the GxEPD2 didn't work for me, so with 6 displays I am running out of gpio pins.
And here is my question. Can I use a I/O multiplexer (like 74HC4051) for each of the CS,DC,RST,BUSY pins, so that I am having just one display object in my code and for each action I address the corresponding pins of the display I want to use via the multiplexer?
... and if this is a bad idea does anyone has another solution for my problem?
You could be more specific, then someone might be able to help.
In general, only CS and BUSY can't be shared. For RST you need the trick shown in the example.
And you could use wired or for BUSY.
Of course you can use a multiplexer for CS.
-jz-
DEPG0290BS has BUSY active HIGH, so use a 6-to-1 or 8-to-1 OR gate.
If you intend to use display hibernate, then you need to specify RST for each. Would need gated RST connections.
Use either a gated multiplexer for CS, or one input of the multiplexer as "enable" for the common CS parameter in the constructors.
thank you for your fast reply. Here is my code to address 2 displays at once which didn't work well.
In my reset_display function I draw the digit 0. In setup I do this first for heimSet1, then for gastSet1. But the digits 0 is being shown simultaneously for two times. So with my setup I think that the displays are not driven separately. After that I draw the digit 4. It is also on both displays but on one the "0" shines through.
#define ENABLE_GxEPD2_GFX 0
#include <GxEPD2_BW.h>
#include <GxEPD2_3C.h>
#include <Fonts/FreeMonoBold9pt7b.h>
#include "digits.h"
GxEPD2_BW<GxEPD2_290_BS, GxEPD2_290_BS::HEIGHT> heimSet1(GxEPD2_290_BS(/*CS=5*/ 35, /*DC=*/ 17, /*RST=*/ 16, /*BUSY=*/ 15)); // DEPG0290BS 128x296, SSD1680
GxEPD2_BW<GxEPD2_290_BS, GxEPD2_290_BS::HEIGHT> gastSet1(GxEPD2_290_BS(/*CS=5*/ 34, /*DC=*/ 17, /*RST=*/ 16, /*BUSY=*/ 2)); // DEPG0290BS 128x296, SSD1680
void setup()
{
Serial.begin(57600);
Serial.println("Es geht los ...");
heimSet1.init();
gastSet1.init();
reset_display(heimSet1);
reset_display(gastSet1);
drawTheDigit(heimSet1,4);
}
void reset_display(GxEPD2_BW<GxEPD2_290_BS, GxEPD2_290_BS::HEIGHT>& display) {
Serial.println("Setze auf Null ...");
display.setRotation(0);
display.setFullWindow();
display.firstPage();
do
{
display.fillScreen(GxEPD_WHITE);
display.drawInvertedBitmap(0, 0,epd_bitmap_0b, 128, 296, GxEPD_BLACK);
}
while (display.nextPage());
}
void drawTheDigit(GxEPD2_BW<GxEPD2_290_BS, GxEPD2_290_BS::HEIGHT>& display, int digit) {
display.setRotation(0);
display.setPartialWindow(0, 0, display.width(), display.height());
display.firstPage();
do
{
display.fillScreen(GxEPD_WHITE);
display.drawInvertedBitmap(0, 0,epd_bitmap_allArray[digit] , 128, 296, GxEPD_BLACK);
}
while (display.nextPage());
}
void loop() {
// put your main code here, to run repeatedly:
}
// create display class instances for each display, each instance with different CS line, each instance with RST disabled,
// (or use separate RST pins for each display),
// each instance with different BUSY line, or BUSY lines or-ed to one pin
// disable reset line to disable cross resets by multiple instances
Didn't you understand what cross resets means?
RST parameter needs be set to -1, so init() will not (cross-)reset the displays.
// one common reset for all displays
digitalWrite(RST_PIN, HIGH);
pinMode(RST_PIN, OUTPUT);
delay(20);
digitalWrite(RST_PIN, LOW);
delay(20);
digitalWrite(RST_PIN, HIGH);
delay(200);
display1.init(115200); // enable diagnostic output on Serial
display2.init(115200); // enable diagnostic output on Serial
display3.init(115200); // enable diagnostic output on Serial
#if defined(ESP32)
display4.init(115200); // enable diagnostic output on Serial
#endif
Added:
I had to re-think and check for the possible cross-reset effect.
Cross-reset would only be an issue if hibernate() is used, as the controller needs reset for wake-up.
The cross-reset on init() isn't an issue, as the controller initialization occurs only at first write to the controller buffer.
You seem to have some other issue. And I don't know if diagnostic output would be of any help.
Could it be that one of your CS lines is stuck at zero?
IO34 6 I GPIO34, ADC1_CH6, RTC_GPIO4
IO35 7 I GPIO35, ADC1_CH7, RTC_GPIO5
... and I connect the BUSY wires of the display to PIN A-G of the IC and connect the BUSY PIN configured in my code to PIN X.
What do I have to do in addition ( -> with diodes and pulldown register for displays with BUSY active HIGH, do you mean pulldown resistor?)? i.e. connect the configured BUSY PIN with a 10 kOhm resistor to ground ...
Yes, this should work. It seems to work in a wide voltage range, and has non-inverted and inverted output. And it is a clean solution.
When I did my proto-board to test with multiple displays, I didn't have a suitable device, and used diodes and a pull-up or pull-down resistor instead. I used both, Pull-down for BUSY active HIGH and pull-up for active low, on two separate IO pins.
