Best way to work with Arduino serial output via BASH?

**holotone** · November 26th, 2014

I have an Arduino Uno running a little script that reads from the SHT-15 temp / humidity sensor, then ouputs the values via serial. The output looks great in the Arduino Serial monitor, and I can even cat the output. The output looks like this:

Code:

temp=68.04
humidity=54.47
temp=68.00
humidity=54.47

When this same Arduino was hooked up to an Eee PC, I would run this command to pull the data off of the serial port and into a txt file:

Code:

ttylog -b 38400 -d /dev/ttyUSB0 | tee /home/holotone/temphumidity/results.txt 2>&1

On the newer computer that the Arduino is connected to, this only produces garbage output, a couple weird characters repeated over and over really fast. The output looks fine via the Arduino serial monitor, and also looks fine when I use cat or picocom.

Ultimately, I want to somehow monitor the serial output of the Arduino and log the results somewhere they are easy to access. Email notification when temp / humidity thresholds are reached is a must. Data visualization (via Google Charts, maybe?) would be awesome.

A buddy helped me whip up a bash script (monitor.sh) to monitor the log file (results.txt) that's supposed to be generated by ttylog (which doesn't work on the new computer); Here is monitor.sh for reference:

Code:

#!/bin/bash

# define file vars
tempfile=/home/holotone/temphumidity/results.txt
logfile=/home/holotone/temphumidity/logfile.log
errorlog=/home/holotone/temphumidity/error.log
max_temp="85.00"
min_temp="63.00"

# extract $temp and $humidity
data=`tail -n 4 $tempfile`
eval $data

# generate timestamp
date=`date +%Y-%m-%d,%H:%M:%S`

# calculate alert threshhold
if [[ "$temp" > "$max_temp" ]]
then
  # send email
  echo "Currently: $temp / Max: $max_temp at $date" | mail -s "Temperature Exceeded!" "me@email.com"
  echo "$date: $temp / $max_temp" >> $errorlog
  echo "Too hot! Currently: $temp; Maximum of $max_temp exceeded!"
else
  echo "Temp OK: Currently: $temp"
fi

# save to logfile
string="$date,$temp,$humidity"
echo $string >> $logfile

# erase existing temp file
echo "" > $tempfile

Basically I moved the setup from an Eee PC on which is was working to a new computer and now nothing works. Step 1 (serial > txt via ttylog) does not work correctly. Even if it did, the monitor.sh bash script doesn't work any more either, even when I manually enter values into the results.txt file that ttylog is not creating correctly. Here's the error I get when I try to run monitor.sh:

Code:

holotone@piff ~/temphumidity $ sh monitor.sh 
monitor.sh: 18: monitor.sh: [[: not found
Temp OK: Currently:

As may be evidenced by my clear lack of understanding, I'm not much of a coder. I get the basics, but I never would have made it this far without the significant help of a friend.

What's going on here? Is there a better way to take the serial output from the Arduino and use it to log historical temp / humidity data and give me notifications when thresholds are reached?

Thanks in advance for the help!

**holotone** · November 26th, 2014

On the advice of a friend I removed the double brackets from line 18 of monitor.sh and that seems to resolve the errors that's throwing. Woohoo! Now I think I just have to get the serial output > text file thing figured out...

**ofnuts** · November 26th, 2014

It should have worked. I works fo me (if I use a file containing lines with "temp=98.00"), so you must have another problem...

The "eval" bit is dangerous, you can fall prey to whatever comes in the file. Better do a proper parsing (sed, awk or else). This could be your problem.

You also have a glaring bug. You are comparing your temperatures using ">" which is a string comparison, so your code is very happy with input temperatures of 100F and above (because alphabetically, 100<65). You should be using numeric comparisons (-lt, -gt, -le, -ge). The work only with integers, but when you parse in your numbers you can either truncate them or transform them to hundreths of degrees (ie, deal with 6500 instead of 65.00).

**holotone** · November 27th, 2014

Originally Posted by ofnuts

The "eval" bit is dangerous, you can fall prey to whatever comes in the file. Better do a proper parsing (sed, awk or else). This could be your problem.

Sorry to be dense, but like I said I'm not much of a programmer - How specifically would I do that? I'm not familiar with sed, awk, or else, but I am decently comfortable using the CLI. To be honest I'm not even sure what 'eval' is doing here.

Originally Posted by ofnuts

You also have a glaring bug. You are comparing your temperatures using ">" which is a string comparison, so your code is very happy with input temperatures of 100F and above (because alphabetically, 100<65). You should be using numeric comparisons (-lt, -gt, -le, -ge). The work only with integers, but when you parse in your numbers you can either truncate them or transform them to hundreths of degrees (ie, deal with 6500 instead of 65.00).

Wow, good eye! I understand the problem, but not specifically how to use those flags - Can you explain?

I noticed something else that was kinda weird happening when I run monitor.sh - It echos this:

Code:

holotone@piff ~/temphumidity $ sh monitor.sh
; Maximum of 85.00 exceeded!

...then creates an empty file called '85.00'. wtf?

**ofnuts** · November 27th, 2014

Originally Posted by holotone

Sorry to be dense, but like I said I'm not much of a programmer - How specifically would I do that? I'm not familiar with sed, awk, or else, but I am decently comfortable using the CLI. To be honest I'm not even sure what 'eval' is doing here.

Hard to give useful hints without knowing how the data looks like. Fror the code you use it seems the file contains lines like "temp=65.30" but I'd like to see a real case.

Originally Posted by holotone

Wow, good eye! I understand the problem, but not specifically how to use those flags - Can you explain?

Instead of:

Code:

if [[ $temp > $max_temp ]]

You use:

Code:

if [[ $temp -gt $max_temp ]]

but this assumes that $temp and $max_temp are integers (so either you drop the fractional part earlier in the code (which, for your purposes, coud be adequate) or you use number that are hundredths of degrees.

Originally Posted by holotone

I noticed something else that was kinda weird happening when I run monitor.sh - It echos this:

Code:

holotone@piff ~/temphumidity $ sh monitor.sh
; Maximum of 85.00 exceeded!

...then creates an empty file called '85.00'. wtf?

This is a direct consequence of your "fix" removing the double brackets. You have a line that bash interprets as:

Code:

65.00 > 85.00

So it tries to find a command called "85.00" and sends its output to a file called "85.00".

**holotone** · November 27th, 2014

Originally Posted by ofnuts

Hard to give useful hints without knowing how the data looks like. Fror the code you use it seems the file contains lines like "temp=65.30" but I'd like to see a real case.

Here's an example of the data if I create it using 'cat </dev/ttyUSB0 | tee results.txt 2>&1':

Code:

Starting up
temp=67.24
humidity=56.34
temp=67.24
humidity=56.31
temp=67.24
humidity=56.31
temp=67.23
humidity=56.27
temp=67.24
humidity=56.31
temp=67.28
humidity=56.31
temp=67.28
humidity=56.34
temp=67.30
humidity=56.28
temp=67.28
humidity=56.37
temp=67.30
humidity=56.34
temp=67.28
humidity=56.34
temp=67.30
humidity=56.35
temp=67.28
humidity=56.35
temp=67.30
humidity=56.28

Originally Posted by ofnuts

Instead of:

Code:

if [[ $temp > $max_temp ]]

You use:

Code:

if [[ $temp -gt $max_temp ]]

but this assumes that $temp and $max_temp are integers (so either you drop the fractional part earlier in the code (which, for your purposes, coud be adequate) or you use number that are hundredths of degrees.

Awesome - I'm not sure how to make sure that the values are integers or how to make them integers if they aren't, but I suspect that's something I can figure out with a bit of googling...

Originally Posted by ofnuts

This is a direct consequence of your "fix" removing the double brackets. You have a line that bash interprets as:

Code:

65.00 > 85.00

So it tries to find a command called "85.00" and sends its output to a file called "85.00".

It seems to do this whether there are double brackets or not.

Thanks again for your patience and help!

**ofnuts** · November 27th, 2014

Code:

temp=$(tail -2 $temp_file | sed -e '/^humidity=.*$/d' -e 's/temp=//' -e 's/\.//') # yields 6580
temp=$(tail -2 $temp_file | sed -e '/^humidity=.*$/d' -e 's/temp=//' -e 's/\.[0-9]*//') # yields 65

In slow motion: get the last two lines of the file (tail -2) then use sed to a) delete the one with "humidity", b) remove "temp=" and c) drop the period or the period and any digits following it.

If you have trouble with the double brackets, then maybe your bash isn't bash but a Korn-like shell... What do you get when you use "/bin/bash --version" on a command prompt? if should answer: