Donald asked 5 years ago
This might be off-off-topic, and not really a question, as I don’t know if Sara & Rui have any tutorials on them. I’ve spent my hobbying time the last two days trying to wrap my head around shift registers and segment LED displays. I’ve got a little digital clock project in mind that I want to incorporate with the ESP32’s wifi capabilities. I’m interested in using the 4 digit 7 segment LED display.
ESP32 Pin Choice: I’ve learned that not any three pins on the ESP32 board (I’m using a 30-GPIO board, Node32S) will work for Latch, Clock, and Data. I initially tried GPIO35,34,and 32. Nope. I searched around and found that GPIO21, 22, and 23 will work; for some reason, pins 4, 12, and 14 also work.
digitalWrite method: The Elegoo starter kit example for Shift Register and 7 segment display uses the shiftOut method, which is successful lighting up the display as expected.
shiftOut(dataPin, clockPin, LSBFIRST, seven_seg_digits[digit]);
works, whereas
digitalWrite(pin,LOW or HIGH)
does not.
In case anyone else has fiddled around with SR, ESP32 and 7 segment displays…these are just my findings.
Sara Santos Staff answered 5 years ago
Hi Donald.
Your first selection of pins probably didn’t work because GPIOs 35 and 34 are input only pins. You can learn more about the ESP32 pins here: https://randomnerdtutorials.com/esp32-pinout-reference-gpios/
When you say the digitalWrite method doesn’t work, what do you mean? To use that method I think you need to wire each pin of the 7-segment display to one GPIO. How are you connecting your display?
Regards,
Sara
Donald answered 5 years ago
Hi Sara,
I think this is one of the examples I was using that didn’t include the shiftOut method.
int DS1_pin = 4;
int STCP1_pin =3;
int SHCP1_pin = 2 ;
int digits [10][8]{
{0,1,1,1,1,1,1,0}, // digit 0
{0,0,1,1,0,0,0,0}, // digit 1
{0,1,1,0,1,1,0,1}, // digit 2
{0,1,1,1,1,0,0,1}, // digit 3
{0,0,1,1,0,0,1,1}, // digit 4
{0,1,0,1,1,0,1,1}, // digit 5
{0,1,0,1,1,1,1,1}, // digit 6
{0,1,1,1,0,0,0,0}, // digit 7
{0,1,1,1,1,1,1,1}, // digit 8
{0,1,1,1,1,0,1,1} // digit 9
};
void display_digit(int d){
if (digits[d][0]==1) digitalWrite(7, LOW); else digitalWrite(7, HIGH); //A
if (digits[d][1]==1) digitalWrite(8, LOW); else digitalWrite(8, HIGH); //B
if (digits[d][2]==1) digitalWrite(9, LOW); else digitalWrite(9, HIGH); //C
if (digits[d][3]==1) digitalWrite(2, LOW); else digitalWrite(2, HIGH); //D
if (digits[d][4]==1) digitalWrite(3, LOW); else digitalWrite(3, HIGH); //E
if (digits[d][5]==1) digitalWrite(5, LOW); else digitalWrite(5, HIGH); //F
if (digits[d][6]==1) digitalWrite(4, LOW); else digitalWrite(4, HIGH); //G
}
void DisplayDigit(int Digit)
{
digitalWrite(STCP1_pin,LOW);
for (int i = 7; i>=0; i--)
{
digitalWrite(SHCP1_pin,LOW);
if (digits[Digit][i]==1) digitalWrite(DS1_pin, LOW);
if (digits[Digit][i]==0) digitalWrite(DS1_pin, HIGH);
digitalWrite(SHCP1_pin,HIGH);
}
digitalWrite(STCP1_pin, HIGH);
}
void setup() {
pinMode(DS1_pin, OUTPUT);
pinMode(STCP1_pin, OUTPUT);
pinMode(SHCP1_pin, OUTPUT);
}
void loop() {
for (int i=0;i<10;i++){
DisplayDigit(i);
delay(300);
}
}
Also, it depends on if your 7 segment display is common cathode or anode…
I *think* I attempted this method using different GPIO pins than 34 and 35.
Sara Santos Staff answered 5 years ago
Hi.
That example will work if you connect each individual pin of the 7-segment display to a single GPIO. Each GPIO controls a segment of the display. That is probably an example based on the Arduino. The A segment is connected to pin 7, the B segment to pin 8 and so on.
void display_digit(int d){
if (digits[d][0]==1) digitalWrite(7, LOW); else digitalWrite(7, HIGH); //A
if (digits[d][1]==1) digitalWrite(8, LOW); else digitalWrite(8, HIGH); //B
if (digits[d][2]==1) digitalWrite(9, LOW); else digitalWrite(9, HIGH); //C
if (digits[d][3]==1) digitalWrite(2, LOW); else digitalWrite(2, HIGH); //D
if (digits[d][4]==1) digitalWrite(3, LOW); else digitalWrite(3, HIGH); //E
if (digits[d][5]==1) digitalWrite(5, LOW); else digitalWrite(5, HIGH); //F
if (digits[d][6]==1) digitalWrite(4, LOW); else digitalWrite(4, HIGH); //G
}
If you want to control it with the ESP32 that way, you need 7 GPIOs, one for each pin of the 7-segment display.
I think you’ll understand how it works if you take a look at this example with Arduino: create.arduino.cc/projecthub/SAnwandter1/programming-4-digit-7-segment-led-display-2d33f8
Let me know if this is clear.
Regards,
Sara