// File : Cascade165.ino // // Version 1, 5 August 2021, by Koepel // Initial version. // Version 2, 5 August 2021, by Koepel // Layout of the wiring made better. // Version 3, 13 August 2021, by Koepel // Changed 'SCK' to 'clockPin'. // Version 4, 17 January 2025, by Koepel // Added pinMode( dataPin, INPUT); // Added a few text labels for the switches. // // Cascade of four 74HC165 shift-in registers. // Only three pins are used on the Arduino board, to read 32 switches. // // Using the 74HC165 is safe, because a pulse to the Latch pin // ('PL' on the 74HC165) will make a new start every time. // In case of an error or a wrong clock pulse by noise, // it synchronizes the data when inputs are read the next time. // // Based on: // (1) // Demo sketch to read from a 74HC165 input shift register // by Nick Gammon, https://www.gammon.com.au/forum/?id=11979 // (2) // 74HC165 Shift register input example // by Uri Shaked, https://wokwi.com/arduino/projects/306031380875182657 // // const byte latchPin = 9; // to latch the inputs into the registers const byte clockPin = 13; // I choose the SCK pin const byte dataPin = 12; // I choose the MISO pin uint32_t oldOptionSwitch = 0; // previous state of all the inputs const int pulseWidth = 10; // pulse width in microseconds void setup () { Serial.begin( 115200); Serial.println( "Turn on and off the switches"); Serial.println( "Top row is switch 0 (right) to switch 7 (left)"); Serial.println( "Second row is 8 to 15, and so on"); pinMode( dataPin, INPUT); // read data pinMode( clockPin, OUTPUT); // clock signal, idle LOW pinMode( latchPin, OUTPUT); // latch (copy input into registers), idle HIGH digitalWrite( latchPin, HIGH); } void loop () { // Give a pulse to the parallel load latch of all 74HC165 digitalWrite( latchPin, LOW); delayMicroseconds( pulseWidth); digitalWrite( latchPin, HIGH); // Reading one 74HC165 at a time and combining them into a 32 bit variable // The last 74HC165 is at the bottom, but the switches start numbering // at the top. So the first byte has to be shifted into the highest place. uint32_t optionSwitch = 0; for( int i=24; i>=0; i-=8) { optionSwitch |= ((uint32_t) ReadOne165()) << i; } for( int i = 0; i<32; i++) { if( bitRead( optionSwitch, i) != bitRead( oldOptionSwitch,i)) { Serial.print( "Switch "); if( i < 10) Serial.print( " "); Serial.print( i); Serial.print( " is now "); Serial.println( bitRead( optionSwitch, i) == 0 ? "down ↓" : "up ↑"); } } oldOptionSwitch = optionSwitch; delay( 25); // slow down the sketch to avoid switch bounce } // The ReadOne165() function reads only 8 bits, // because of the similar functions shiftIn() and SPI.transfer() // which both use 8 bits. // // The shiftIn() can not be used here, because the clock is set idle low // and the shiftIn() makes the clock high to read a bit. // The 74HC165 require to read the bit first and then give a clock pulse. // byte ReadOne165() { byte ret = 0x00; // The first one that is read is the highest bit (input D7 of the 74HC165). for( int i=7; i>=0; i--) { if( digitalRead( dataPin) == HIGH) bitSet( ret, i); digitalWrite( clockPin, HIGH); delayMicroseconds( pulseWidth); digitalWrite( clockPin, LOW); } return( ret); }