How to calculate checksum?

[I14R10]

Weather station is sending packets of 48 bits. Last 4 are checksum of all previous. For example, this is a real packet.

1001 0100 0100 1111 0101 1000 0100 0101 0100 1011 1010 and checksum is 1111

How is this checksum calculated?

 

[barry]

Could be just about anything. Maybe just a running sum of all data. Maybe something totally different.

I would look at some other packets and see if my running sum theory is correct.

 

[I14R10]

OK, so there is not only one way to calculate checksum, like: count of all "1"s in a signal?

 

[xenos]

Have you checked if it's just a simple checksum using a calculator before posting question?

#include <stdio.h>

#define N	12

const char *n[N] = {
	"1001",
	"0100",
	"0100",
	"1111",
	"0101",
	"1000",
	"0100",
	"0101",
	"0100",
	"1011",
	"1010",
	"1111"
};

unsigned tra(const char *s){//binary string to unsigned
	unsigned x = 0;
	while(*s){
		x <<= 1;
		if(*s == '1')
			x |= 1;
		s++;
	}
	return x;
}

void get(unsigned *v,const char **n,int k){
	while(k-->0)
		v[k] = tra(n[k]);
}

unsigned add(unsigned *v,int n){
	unsigned sum = 0;
	while(n-->0)
		sum += v[n];
	return sum;
}

int main(void){
	unsigned v[N];
	get(v,n,N);
	printf("sum= %x\n",add(v,N-1));
	return 0;
}

result:
sum= 4f

It could be the last 4 bits of the checksum of the first 11 elements.
It seems ok for this packet.
Of course you need more packets to confirm it.

 

[barry]

OK, so there is not only one way to calculate checksum, like: count of all "1"s in a signal?

There are many, many,many ways to calculate a checksum. The documentation for your device should tell you what method it uses.