Temperature Conversion 2 byte

Question

I have difficulty in converting two bytes in temperature. I have a control unit (temperature sensor) where I get the message of temperature with two bytes.

1 ) Example:

message: [ 40 ][ 25 ]
LSBYTE : [ 40 ]
MSBYTE : [ 25 ]
0.03125 C/bit
temperature: 25C° ( seen from the display of the control unit )

2 ) Example:

message: [ 40 ][ 26 ]
LSBYTE : [ 40 ]
MSBYTE : [ 26 ]
0.03125 C/bit
temperature: 30C° ( seen from the display of the control unit )

3 ) Example:

message: [ 20 ][ 26 ]
LSBYTE : [ 20 ]
MSBYTE : [ 26 ]
0.03125 C/bit
temperature: 32C° ( seen from the display of the control unit )

4 ) Example:

message: [ c0 ][ 25 ]
LSBYTE : [ c0 ]
MSBYTE : [ 26 ]
0.03125 C/bit
temperature: 29C° ( seen from the display of the control unit )

I do not know how to convert the message in temperature.

I ask for your support. who can give me a solution, it can collaborate in my project ( create a app android to receive messages from the control unit )

Garr Godfrey · Answer 1 · 2014-09-09T09:33:41.647

0

It appears to be giving you the whole temp in the upper byte, and the fraction in the lower byte. That would be 25.15625 (25 + 40/256).

I don't know where the 0.03125 C/bit comes from. That would mean 16bits = 0.5C. Seems like nonsense.

the other possible explanation is that .03125 * total = degrees C. If MSB is 25 and LSB is 40, the total is 201.25 degrees. so...probably not right.

EDIT: 0.03125 = 1/32

none of your points use the last 5 bits. that is fractional component. Take upper byte, lower byte, and shift right 5 bits then subtract 273 (for kelvin to C conversion).

edited Sep 09 '14 at 09:33

answered Sep 09 '14 at 08:45

Garr Godfrey

8,257
2
25
23

thanks for your reply, but it is not the right formula, because taking another message : '[40][26] temperature is 30 C° – Alessandro Anselmo Sep 09 '14 at 08:49
A believe a datasheet for your module would be helpful here. – Jitsu Sep 09 '14 at 08:53
you data doesn't make sense. It isn't even linear. however, it is close to a kelvin amount if you take the full 2-byte number and multiply by 0.03125. – Garr Godfrey Sep 09 '14 at 09:26
(MSBYTE*256 + LSBYTE)/32 - 273 <-- my numbers in decimal. Your numbers in hex. – Garr Godfrey Sep 09 '14 at 09:37
the solution is : if i have a example message: [20][26] and the temperature is 32C° the fomula is : 2620 in decimal is 9760 (9760 * 0.03125)-273.15= 31.85 = 32C° – Alessandro Anselmo Sep 09 '14 at 10:02

score 0 · Answer 2 · answered Sep 09 '14 at 08:51

0

This is simply Little endian byte order. Your most important byte would be the MSB. It looks like it's natively in celsius. So simply read it like this (please excuse the pseudo-code):

var msbyte = read() // whatever you need to get the value
var lsbyte = read() // whatever you need to get the value

var temperature = msbyte
temperature += (lsbyte / 100)

In your case its simply 25.40C°

answered Sep 09 '14 at 08:51

Jitsu

769
3
7

thanks for your reply, but it is not the right formula, because taking another message : [40][26] temperature is 30 C° – Alessandro Anselmo Sep 09 '14 at 08:54

score 0 · Accepted Answer · answered Sep 09 '14 at 10:04

0

the solution is : if i have a example message: [20][26] and the temperature is 32C° the fomula is : 2620 in decimal is 9760 (9760 * 0.03125)-273.15= 31.85 = 32C°

answered Sep 09 '14 at 10:04

Alessandro Anselmo

29
1
5

Temperature Conversion 2 byte

3 Answers3

Linked