PISO Shift Register problem with input 3 and 4

Other Hardware LEDs and Multiplexing
1

Hey Guys,

I am struggling with this issue for quite a while now.

I am using a 74HC 165 PISO Shift Register to control input of eight buttons. Everything works fine except button 3 and 4. Button 3 gives no input at all and button 4 is recognized as either 3 or 4. All other button's signals are as they are supposed to be.

This is my code:

int latchPin = 8;
int dataPin = 9;
int clockPin = 10;
int enablePin = 11;

void setup() {
    Serial.begin(9600);

    pinMode(enablePin, OUTPUT);
    pinMode(latchPin, OUTPUT);
    pinMode(clockPin, OUTPUT);
    pinMode(dataPin, INPUT);
}

uint8_t myShiftIn(int dataPin, int clockPin) {
    uint8_t shiftValue = 0;
    byte x;

    for (x = 0; x < 8; ++x) {
        digitalWrite(clockPin, LOW);
        shiftValue |= digitalRead(dataPin) << (7 - x);
        digitalWrite(clockPin, HIGH);
    }
    return shiftValue;
}

void loop() {
    digitalWrite(latchPin, LOW);
    delayMicroseconds(20);
    digitalWrite(latchPin, HIGH);

    digitalWrite(enablePin, LOW);
    uint8_t bitFieldButtonPressed = 
    myShiftIn(dataPinInput, clockPin);
    digitalWrite(enablePin, HIGH);
    
    for (int i = 0; i < config::shelfCount; i++) {
        if (bitFieldButtonPressed & (1 << i)) {
            Serial.println(i);
        }
    }
}

I connected enablePin to clockInhibit of Shift Register, latchPin to Shift/Load, clockPin to clock and dataPin to QH.

When I press the first button, my code outputs 0,
for the second button it is 1,
for the third button it is nothing,
for the fourth it is either 2 or 3, I see no pattern here.

All other buttons work correctly.

The third and fourth button are soldered correctly. I tested them individually by plugging them into my arduinio directly and they work. But they do not in combination with my shift register.

I bougth three brand new PISO shift registers of the same model and the result is always the same. So I can exclude the shift register from being the problem.

I already did plenty of internet research but I found nothing helpful.

DataSheet This is a data sheet from the shift register I am using. It is provided by Reichelt Elektronik and the link redirects to a Reichelt Elektronik site.

Thank you very much for any help.

Kind regards,
Hendrik

2

When I press the first button, my code outputs 0,
for the second button it is 1,

Where in the code does this output happen, I can’t see it.

Why does your loop function which is not supposed to return anything return a value?

3

First of all, thank you for your reply.

Grumpy_Mike:
Where in the code does this output happen, I can’t see it.

This is in fact a little bit misleading, my bad. I changed the return to a Serial output. But it changes nothing on my general problem.

4

Did you use (10k) pull up or pull down resistors with your buttons.
A floating pin, when no button is pressed, can drift to any logic state.
Leo..