Having trouble with a potentiometer controlling some LEDs

Projects Programming
1

I have 5 LEDs a potentiometer and a m74hc59581 shift register.
As far as I know, everything is correct but no LEDs will light when I twist the pot.
Here is the code, if this isn't it I'll assume I looked at a bad datasheet for my shift registers pinoutpinout.

int dataPin = 8;
int latchPin = 10;
int clockPin = 12;
int potPin = A0;
int val = 0;
int shiftVal = 0;

void setup()
{
  pinMode (latchPin, OUTPUT);
  pinMode (clockPin, OUTPUT);
  pinMode (dataPin, OUTPUT);
  pinMode (potPin, INPUT);
}

void loop()
{
  digitalWrite(latchPin, LOW);
  val = analogRead(potPin);
  val = map(val, 0, 1023, 0, 25);
  if (val >= 0 && val < 5) {
    int shiftVal = 64;
  }
  else if (val >= 6 && val <= 10) {
    shiftVal = 96;
  }
  else if (val >= 11 && val <= 15) {
    int shiftVal = 112;
  }
  else if (val >= 16 && val <= 20) {
    int shiftVal = 120;
  }
  else if (val >= 21 && val <= 25) {
    int shiftVal = 124;
  }
  else {
    int shiftVal = 0;
  }
  shiftOut(dataPin, clockPin, MSBFIRST, shiftVal);
  digitalWrite(latchPin, HIGH);
}
2 
  if (val >= 0 && val < 5)
  else if (val >= 6 && val <= 10)
  else if (val >= 11 && val <= 15) {

Suppose val is 5. What happens?
If val is less than 10, the 1st of second if blocks deal with that situation. The val >= 11 part is unnecessary, because val has to be greater than 10 in order to have gotten by the first two checks. The same holds true for all the other compound if tests, except the first one, where, apparently, the value of 5 is to be explicitly ignored (or not).

Here is the code, if this isn't it I'll assume I looked at a bad datasheet for my shift registers pinoutpinout.

Or you have the LEDs in backwards.

3

Hi

I am a newb myself...but I would suggest you try changing:

val = analogRead(potPin);
val = map(val, 0, 1023, 0, 25);

to something like

int valPot=0;

valPot = analogRead(potPin);
val = map(valPot, 0, 1023, 0, 25);

are you sure that is otherwise the full sketch?

daniel

4

but I would suggest you try changing:

val = analogRead(potPin);
val = map(val, 0, 1023, 0, 25);

to something like

int valPot=0;

valPot = analogRead(potPin);
val = map(valPot, 0, 1023, 0, 25);

Why? The codes are functionally identical, except the second wastes and extra int (and sets it to zero unnecessarily).

5

OK, so I guess that won't help then!Just suggesting what (I thought) I had learnt..... :blush:

daniel

6

Suppose val is 5. What happens?
If val is less than 10, the 1st of second if blocks deal with that situation. The val >= 11 part is unnecessary, because val has to be greater than 10 in order to have gotten by the first two checks. The same holds true for all the other compound if tests, except the first one, where, apparently, the value of 5 is to be explicitly ignored (or not).

This was clearly a mistake(I'm surprised you couldn't tell), but the last else statement would have caught it. I have triple checked my LEDs too.

are you sure that is otherwise the full sketch?
daniel

Yep, all hand typed, ctrl+a - ctrl+c to copy it all.

7

This was clearly a mistake(I'm surprised you couldn't tell)

If I couldn't tell, I probably wouldn't have mentioned it.

8

Turns out I wasn't supposed to declare an analog pin as input/output.