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Message ID: 13     Entry time: Wed Dec 12 16:19:00 2007
Author: tobin 
Type: Lab Infrastructure 
Category: HVAC 
Subject: Lab Temperature 
I connected the particle counter to the Dell computer for PEM data logging (temperature, humidity, and particle count). The data shows that while the temperature is comfortable right now, it was quite warm in here yesterday (78 degrees). A plot is attached.

For this I made a serial cable using two DB9-to-RJ45 converters and a length of Cat5 ethernet cable. The computer end of the cable has a female connector; the particle counter end of the cable has a male connector. Only three conductors are connected: transmit (pin 2), receive (pin 3), and ground (pin 7 on the particle connector, pin 5 on the computer). I used the USB-to-serial dongle, which shows up in Linux as /dev/ttyUSB0.

Someone later can write a script to automatically poll the particle counter for new data. For now, I just emptied its internal buffer, which stores the last 200 measurements. The secret to communicating with the particle counter, which I learned by examining the c1psl statecode at the 40m, is to first transmit the letter "U". After this, the particle counter will listen to you and do what you say. In particular, sending a capital letter "A" will cause the counter to emit the next measurement from its buffer, until there are none left, at which time it will just respond with "#". To read the data I just ran a "cat /dev/ttyUSB0" command in one terminal, while in another terminal I ran a loop "while 1; echo -n A > /dev/ttyUSB0; sleep 1; end". I set the serial port parameters (9600BPS, 8N1) using Minicom.

Also, there's a Matlab script to parse and plot the output, in ~controls/tobin.
Attachment 1: temperature.pdf  14 kB  | Show | Show all
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