Hi,
I'm new to Forum and fairly new to Arduino.
I hope I did OK with the code. I put it in code tags:slightly_smiling_face:
I'm reading DS18B20 temp sensor and use UNO R3.
I get the correct temperature on the serial monitor.
But I want to display the value on an LED matrix display (built of 3x 8x8 WS2812B RGB LED arrays). Displaying time ( with other sketch) is no problem.
I convert the float tempC via memcpy() into 4 bytes.
I was hoping to be able to extract the temperature from these. I understand the DS18B20 2byte format for temperature.
First I send the 4 bytes to the serial monitor. But I do not fully understand the meaning.
Serial monitor shows e.g.:
16.31°C bin 0 10000000 10000010 1000001
Extracted temperature: 0 10000000 1|0000|010 1|000001
which is 16 5x0.0625
But why for instance is the last byte 1000001, so 7 bits iso 8 bits.
And apparently when byte=00000000 it is shown as 0, that is OK.
16.25°C bin 0 0 10000010 1000001
Extracted temperature: 0 0 1|0000|010 1|000001
which is 16 5x0.0625
Why is byte content the same as for 16.31°C except for the 2nd byte (0 vs 10000000) ?
17.37°C bin 0 0 10001011 1000001
Extracted temperature: 0 0 1|0001|011 1|000001
which is 17 7x0.0625
-4.19°C bin 0 0 10000110 11000000
I didn't try extracting this one yet, but I expect to be able to do this (I think something like 128- value) when the above is clear to me.
#include <DallasTemperature.h>
#include <OneWire.h>
#define ONE_WIRE_BUS 10 // 1-Wire bus data pin
OneWire oneWire(ONE_WIRE_BUS);
DallasTemperature sensors(&oneWire);
void setup() {
Serial.begin(9600); // start serial port
sensors.begin(); // Start up the DallasTemperature library
sensors.setResolution(12); // Set up the resolution for our sensors
}
void loop() {
sensors.requestTemperatures(); // Send the command to start the temperature conversion
float tempC = sensors.getTempCByIndex(0);
byte b[4] = { 0 };
memcpy(b, &tempC, sizeof(b)); // copy float tempC into 4 bytes
// Check if reading was successful
if (tempC != DEVICE_DISCONNECTED_C) {
Serial.print(tempC); // Print temperature of device 1 (index 0)
Serial.print("°C bin ");
for (int i = 0; i < 4; i++) // send the 4 bytes to monitor
{
Serial.print(i);
Serial.print("=");
Serial.print(b[i], BIN);
Serial.print(" ");
}
Serial.println(" ");
} else {
Serial.println("Error: Could not read temperature data");
}
}
Yes, of course. But I would then need the individual digits (tens, units, decimal) and would like some guidance how to extract these.
Regards, Hobbybok
I would like to extract the digits (binary, hex or BCD). E.g. 16.31°C >> 1 6 3(rounded).
I have briefly looked at IEEE 754 - Wikipedia but that didn't really help, very complicated as you say.
And if the byte representation as I have tried was clear to me (why is last byte only 7 bits and sometimes 8 bits as for negative temp) I can write code to extract. That is the fun of programming
That's easy. Say you have 1234
divide by 1000 will give you 1
by 100 gives 12
by 10 gives 123
Subtract 123x10 from 1234 and you have 4
Subtract 12x10 from 123 and you have 3
Subtract 1x10 from 12 and you have 2
2.16.31 (1) Codes executed to get Temperature data:
byte myData[9];
ds.read_bytes(myData);
(2)
Lower 4-bit of myData[0] holds fractional part (0.3100, Fig-1).
Uppler 4-bit of myData[0] and lower 3-bit of myData[1] holds integer part (16, Fig-1 & Fig-2).
(3) Extracting 1 and 6 from 16 ===> 0001, 0006 : D1, D0
