INTERVIEW VIKAS VINAYAK CEO & CO-FOUNDER ... - EEWeb

The SPI interfaces to the max chip using a 32
bit block of data. However the pre-written function
within the mbed that allows direct access
to the SPI bus only goes up to a 16 bit format.
This would have made interfacing to the device
as easy as the NTC and analog pins. However
SPI is really easy to deal with anyway, so below
I have written my own code to interface to the
device.
You will see that I only need the block of bits
from bit 1 (where 0 is the first) to 11. The rest
are thrown away. A little shift register in c code
and you can quickly get your data from the max
chip. I really should look at the
timings on a scope but it’s working
right now -- I will check the
details later on but I suspect I’m
well within limits.
Output Code
SPI_Code
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The last thing I’ll need to add this time round is
a serial connection to use for debugging and
then later for our Xbee.
Once again this is really easy to add to your
mbed. Add the Serial class with the pre-defined
RX and TX pins and then install the mbed USB
to serial driver on your PC, and you are done!
I use a small free program
called putty.exe that can be
used as a serial terminal. Set
the baud rate to 9600 and
coms port (you can find this
in device manager under
“Serial Ports” in Windows)
and then you can get data
from your mbed.
Last thing to do this time
round is to send the collected
data, one second at a
time, and send it over the serial
port (code below). The
data from the NTCs is still
raw ADC counts and not in
T’c as yet but the data from
the max chip is.
Output Code
Next time I will turn the raw
ADC counts into T’c and also
look at storing the data on the mbed’s flash.
If you would like to see the full code you can
download it form here: http://mbed.org/users/
monpjc/code/temperature_logger_Pt2/
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