Map function weird behaviour

Using Arduino Programming Questions
#1

Hello,

I'm trying to use my Arduino to log Throttle Possition Sensor reading from my motorcycle to SD Card.

But readings returned by map value are weird.

Thats how I do that:

const int TPSin = A0;
byte TPS = 0;

void setup(){
pinMode(TPSin, INPUT);

}

void loop(){
int TPSReading = analogRead(TPSin);
TPS = map(TPSReading, 0, 1023, 0, 100);
}

And then map return good values most of the time, but sometimes that give me 255 (max byte value). Why?

#2

Have you tried printing TPSReading before using the map() function ?

What exactly is connected to the analogue input ?

#3

No, I haven't. I'll try today.

I've connected TPS output to analog input. TPS (3-wire) is potentiometer where resistances change with throttle openning.

#4

Thing is, in the example you don’t even print the outcome… :wink:

Extra note, map(x, 0, 1023, 0, 100) looks okay but actually doesn’t make for a nice curve. Only value 1023 will map to 100 (where as for example the whole range 52 to 60 maps to 5). map(x, 0, 1024, 0, 101) will give a nicer result :slight_smile:

#5

Yeah, I know example doesn't print, because that's just part for mapping.

Actually I use ESP32, then map for me looks like:

TPS = map(TPSreading, 250, 2130, 0, 100);

And most of the time that give me nice 0 - 100% :slight_smile:

#6

Yeay, it will indeed output 100 if the input is 2130. But it will ONLY output 100 when input is 2130. Where as it will output 1 for the full input range of 269 to 287. Doing map(TPSreading, 250, 2131, 0, 101); fixes that :slight_smile:

#7

Actually I use ESP32, then map for me looks like:

TPS = map(TPSreading, 250, 2130, 0, 100);

What are you expecting map() to return if TPSreading is 249?

#8