control relays using 74hc595(shiftout) - arduino

Question

I want to use 7h4c595(8 IOs) to control 8 relays.
I tried using 0b00000000, It's working fine.
but I don't know how to concat switches values into this kind of binary.
almost 0 knowledge about this. sorry
I know the code below is not right, but it seems working.
problem: 74hc595's q0 is controling the 2nd relay, not the 1st.
and q1 is controling 3rd relay.
It should be like q0->1st, q1-> 2nd, and so on.
sorry for bothering you.
[code]
uint8_t switch0=0;// 0 = off
uint8_t switch1=1;// 1 = on
etc...
uint8_t switch7=1;//1-7 on
setup(){
etc...
}
loop(){
if(digitalWrite(btn1)==HIGH){
switch0=1;//on
switch1=0;//off
etc...//1-7 off
}
//unit8_t sw=0b10000000; //turn 1st relay on when btn1 pressed
uint8_t sw={switch0,switch1,....,switch7};
for(int i=0;i<8;i++){
digitalWrite(latchPin, LOW);
shiftOut(dataPin, clockPin, MSBFIRST, i);
digitalWrite(latchPin, HIGH);
}
}

Answer 1

I'd go in similar way how are the pins defined in avr/io.h
constexpr uint8_t RELAY0 = 0;
constexpr uint8_t RELAY1 = 1;
// ...
constexpr uint8_t RELAY7 = 7;
loop() {
uint8_t data = (switch0 << RELAY0) | (switch1 << RELAY1) | /* ... |*/ (switch7 << RELAY7);
digitalWrite(latchPin, LOW);
shiftOut(dataPin, clockPin, MSBFIRST, data);
digitalWrite(latchPin, HIGH);
delay(200); // or more
}
Or you can use single byte (uint8_t) for storing all switches at once. As a bonus you can send it over shiftOut directly.
uint8_t allSwitches = 0; // all relays disabled
// turning relay x on (somewhere inside of function):
allSwitches |= _BV(x); // where x is number between 0 and 7 including
// turning relay x off:
allSwitches &= ~_BV(x);
// but you can set some of them and reset others in single step:
allSwitches = _BV(0) | _BV(5) | _BV(7); // turns on relay 0, 5 and 7, rest will be turned off