Temperature sensor example

initialization

The following is a script that I use to initialize the temperature sensors for the rpi_ui board.

#!/bin/sh
ui="bw_tool -a 94"
#ui="bw_tool -a 94 -I -D /dev/i2c-1"
$ui -w 70:c7 # internal tempsens with internal 1.1V as reference
$ui -w 71:c6 # external tempsens with internal 1.1V as reference
$ui -W 81:1000
$ui -w 82:6
$ui -w 80:2

The above script is written for the SPI version of the board. The commented out like is for the i2c-version. So activate that line if you have the i2c version (remove the comment marker).

readout

The following is a script that shows the temperature on stdout. I call this script "showtemp".

#!/bin/sh
# 
#
# Set the number of samples to 64, and shift by 0, or set the 
# number of samples to 4096 and shift by 6. The latter is recommended!
#
adcmaxval=65520
#adcmaxval=1023
#
# MCP9700 degrees per volt. 
vperdeg=0.010
#refvoltage=4.9000
refvoltage=1.1000
# mcp offset voltage is 500mv at 0 deg. At 0.010 volt per deg that comes to 
# 50 degrees C. 
offset=50
#
#
# 60 adc channel 0, direct value (0-1023)
# 68 adc channel 0, averaged value (0-65520 with nsamp=4096, shift=6)
# 61 adc channel 1, direct value (0-1023)
# 69 adc channel 1, averaged value (0-65520 with nsamp=4096, shift=6)
register_to_read=69

#
# settings are done, now the preparations. 
convfactor=`(echo scale = 10 ; echo obase=16;echo $refvoltage / $vperdeg / $adcmaxval ) | bc`
offsethex=`(echo obase=16; echo scale=3;echo $offset) | bc `


# now do the real deal. 
rawtemp=`sudo bw_tool -s 100000 -a 94 -R $register_to_read:s | tr a-z A-Z`
(echo ibase=16; echo scale=3;echo $rawtemp \* $convfactor - $offsethex)  | bc

display

The following clears the screen and then shows the temperature.

bw_tool -a 94 -w 10:0
bw_tool -a 94 -t "temp: "`./showtemp`