Send ECG signal with NRF24L01 from Arduino to Raspberry Pi 3
I see multiple flaws in your code:


radio.write(&amp;s, sizeof(s)); does not what you think it would. The correct statement would be radio.write(s, sizeof(s)); without the ampersand.
You are using double. Not using floating point numbers at all would be preferable.
Your s is of type byte. Thus it only holds 8 bytes. So your floating point calculations are being truncated to the range [0, 255]. From your problem description this is not what you are trying to achieve, I think.