- Mon Jan 19, 2015 12:06 pm
#7717
Hmmm... I am facing a few problems!
I have a sensor that outputs temperature data in two 8bit wide registers. Reg1 (15:8) and Reg2(7:0).
I have to connect those registers into one and make one 16bit signed quantity! Then to get the actual temperature value I have to divide this by 340 and add 36.5
Something like 16bit_SignedNumber/340+36.5
I am reading the two 8bit registers (Reg1 = RegH and Reg2 = RegL) and using this code to get the temp:
T = (string.byte(RegL) and string.byte(RegH) * 256)/340 + 36,5
It seems that is not working properly! I am getting strange values! Any idea of how I will solve this problem?
I have a sensor that outputs temperature data in two 8bit wide registers. Reg1 (15:8) and Reg2(7:0).
I have to connect those registers into one and make one 16bit signed quantity! Then to get the actual temperature value I have to divide this by 340 and add 36.5
Something like 16bit_SignedNumber/340+36.5
I am reading the two 8bit registers (Reg1 = RegH and Reg2 = RegL) and using this code to get the temp:
T = (string.byte(RegL) and string.byte(RegH) * 256)/340 + 36,5
It seems that is not working properly! I am getting strange values! Any idea of how I will solve this problem?
- Mon Jan 19, 2015 1:33 pm
#7725
Why not use something like
Code: Select all
T = ((string.byte(RegL) + string.byte(RegH) * 256)/34 + 365)
print("Temperature: "..(T/10).."."..(T%10)..")
- Mon Jan 19, 2015 7:10 pm
#7759
I can see that we are going to have to do some brain gymnastics with our formulas to make them stay out of floating point land and then just cut them down to size when it is time to do something with them!!
Another example or two would really help to get my brain into gear.
And I realised that I have a need to calculate lux from the output of a TSL2561 sensor.
There are several formula in the datasheet dependant on the ratio of CH1/CH2 (both 16 bit values) like this:
Lux = 0.0304*CH0 − 0.062*CH0*((CH1/CH0)1.4) -- (that is raise to the power of 1.4)
or
Lux = 0.0128*CH0 − 0.0153*CH1
Now the datasheet (and the every-bountiful adafruit example library for arduino) embody a method of doing this without floating point, but I can't quite follow all the twists and turns, and anyway, I'm sure there are more elegant ways of doing this in lua. My attempt at the simpler formula is this:
Lux=(128 * CH0 - 153 * CH1 ) / 10000
Am I on the right lines - and how would one be able to do the more complex one? datasheet is here http://www.datasheetlib.com/datasheet/867868/tsl2561_pacer-international.html?page=22#datasheet (html doesn't show calculations properly
- pdf does - http://www.adafruit.com/datasheets/TSL2561.pdf
I don't know enough maths to begin to even think about how to do powers
Another example or two would really help to get my brain into gear.
And I realised that I have a need to calculate lux from the output of a TSL2561 sensor.
There are several formula in the datasheet dependant on the ratio of CH1/CH2 (both 16 bit values) like this:
Lux = 0.0304*CH0 − 0.062*CH0*((CH1/CH0)1.4) -- (that is raise to the power of 1.4)
or
Lux = 0.0128*CH0 − 0.0153*CH1
Now the datasheet (and the every-bountiful adafruit example library for arduino) embody a method of doing this without floating point, but I can't quite follow all the twists and turns, and anyway, I'm sure there are more elegant ways of doing this in lua. My attempt at the simpler formula is this:
Lux=(128 * CH0 - 153 * CH1 ) / 10000
Am I on the right lines - and how would one be able to do the more complex one? datasheet is here http://www.datasheetlib.com/datasheet/867868/tsl2561_pacer-international.html?page=22#datasheet (html doesn't show calculations properly
- pdf does - http://www.adafruit.com/datasheets/TSL2561.pdfI don't know enough maths to begin to even think about how to do powers
