Monitoring Vehicle Voltages

Wow!

My last post was in March!
I certainly enjoyed the summer and am looking forward to spending more time back on the bench.

I did stay tinkering during the summer with interconnecting my Raspberry Pi's with Arduino Nano's and Uno's.

The pic below shows my Raspberry Pi connected via USB to my Arduino Uno. I use the analog inputs on the Arduino to monitor the battery voltages in a couple of vehicles that I don't drive every day and to copy that up to a webpage

The small circuit board in the upper right corner is a DC - DC converter and I use it to convert 12VDC down to 5VDC for the Pi and Arduino. It is rated for 5A, so I should have lots of capacity. I've started using Anderson Powerpoles for all of my 12V circuits in my garage and ham shack for interoperability.

Having the power supply on the board also allows me to use a homebrewed POE cable so that I can power and communicate with the Raspberry Pi with one ethernet cable. 4 wires are used for communication and 4 for power (2 + & 2-),

I've also wanted to move away from the Arduino IDE because I usually spend my time ssh'ing into my devices. So I've come across an awesome program arduino-mk which allows you to edit the .ino files with your favorite editor and then use their Makefile to upload it to the arduino. I've successfully used this with the GertDuino, Arduino Nano, and Arduino Uno.

Thanks for visiting;
Robin

Update on posting to aprs.fi

Things have been quite hectic around here for the last few weeks so I haven't had a chance to post. I been asked to add some additional detail to the process I use to send my house / outdoor / & garage temperatures to aprs.fi.

I've updated my git repository (www.github.com/robingreig/raspi-git/aprx) with the latest files.
***** aprx.conf is now my configuration file with all of the custom beacon files included *****

beacon01.txt is the actual beacon file that transmits the temperatures & is beaconed every 10 minutes
T#136,22.5,38.7,15.7,0,0,00000000
T# = Telemetry
136 is my unique number (0 to a maximum of 999) each day.
***I take temperature readings every 10 minutes and save them to the file, then I take the  # of minutes since midnight for this beacon file / 4 to give me a unique number and copy that to this text file
So the unique number for my first beacon file should be 10 minutes past midnight / 4 = 2
Second unique number for the second beacon file = 20 minutes / 4 = 5
Since there are 1440 minutes in a day (24 hours x 60 minutes) / 4 my maximum beacon number would be 360 each day before it resets.
22.5 = House Temperature
37.7 = Outside Temperature + 40
*** Remembering that the number sent has to be between 0 & 255, if it is cold and I have a negative temperature, it won't send properly. So, worst case my outside temp would be -40C, so I add 40 to the outside temp so even worst case, my number would be 0. Then within my equations text file, I subtract 40 off the number to return to the actual outside temperature.
15.7 = Garage Temperatur
0,0,00000000 are additional values that are not used, but in my experience I needed to add them to the string for it to be recognized properly.

beacon02.txt is the parameters file and is beaconed every 120 minutes
:VE6RBN-1 :PARM.House Temp,Outside Temp,Garage Temp
This is a static text file that is beaconed, it does not change, since my parameters don't change

beacon03.txt is the units of measure file and is beaconed every 120 minutes
:VE6RBN-1 :UNIT.Deg C,Deg C,Deg C
This is a static text file as well and doesn't change.

beacon04.txt is the equations file and is beaconed every 120 minutes
:VE6RBN-1 :EQNS.0,1,0,0,1,-40,0,1,0
There are 3 variables sent for every parameter
House Temp (first set of 3) = 0, 1 , 0
Outside Temp (second set of 3) = 0, 1, -40
Garage Temp (third set of 3) = 0, 1, 0
First number of the set is used if we want to square the variable ( which I don't need to do)
Second number is a multiplier (I don't want to multiply my value, so I set it to 1, value x 1 = value)
Third number is a value to add to your variable.
Remembering that I added 40 to my outside temperature, here I subtract 40 from my outside variable to bring the value back to where it should be.

The only other point I wanted to bring up was that I haven't had time to experiment with sending these values out over the air, so I've set my 3 static beacon files (beacon02, beacon03, & beacon04) to be sent out over the internet only. As time allows I want to play with sending this information out over the air in a way that will be displayed properly.

Thanks for reading,
Robin

Posting Temperature on APRS.fi

I've been working on understanding how telemetry data is sent via APRS. I found a good link on the APRS Site.

It showed me the format of the Telemetry String: T#sss,111,222,333,444,555,xxxxxxxx.

T# defines the string as a telemetry string.

They referred to the first set of numbers (sss) as the serial number and I found that it had to be a unique number from 1 - 999, each day.
I take that to mean that one could only send 999 telemetry packets over the course of the day.

The following 5 groups (111,222,333,444,555) are 5 different 3 digit, analogue values that need to be between 0 - 255.

And the final 8 are binary values which could show (open doors, devices on/off, etc)

So the first challenge I had was to determine how to setup a unique 3 digit number for each transmission, that would reset each day. I decided to go with time.
There are 24 hours x 60 minutes = 1440 minutes in a day, so that is more than 999 & won't quite work.
But I could take the total minutes of the day and divide it by 4.
Here is the Python code that I'm using:
I use the "if DEBUG > 0:" statements to print out values to help me debug a problem. Once it is working properly, I set DEBUG to 0 so they won't print during the execution of the program.

  aprs_hour = int(time.strftime("%H"))

  if DEBUG > 0:

    print "aprs_hour: ", aprs_hour

  aprs_minute = int(time.strftime("%M"))

  if DEBUG > 0:

    print "aprs_minute: ", aprs_minute

  aprs_time = int((aprs_hour * 60) + (aprs_minute)) 

The second challenge that I encountered was the outside temp.
Initially I expected to send the raw value with no problem.
February in Calgary doesn't generate positive values (grin) and so I was stuck for a bit when I saw the correct numbers being sent (-13.6 to -15.0 deg C on the day of my test) but the graph didn't move off of 0.
Then I remembered the values needed to be between 0 - 255.
Assuming the coldest temp of -40C I simply added 40 to the existing temp to bring it to a positive value and then had to figure out how to bring it back to the actual values in aprs. 

After further research, I found out about the EQNS aprs string.
Each analogue value is placed into a quadratic equation and one can send the values to modify it.
There are 3 numbers sent for each analogue value as follows:

EQNS.abc,def,ghi,jkl,mno

Since analogue value #2 is for my outside temperature, there are 3 values d, e, f that will be placed in the following equation: (Value of #2 x d2) + (Value of #2 x e) + f

So in my case of the negative outside temp, I converted it to a positive by adding 40 to it before it was sent.
My numbers for Value #2 were 0,1,-40. 0 because I didn't want to square it, 1 because I wanted the value and -40 because I had added 40 to the original value, and now needed to subtract it. 

I've setup aprx to send out these 3 fields every 120 mins:

:VE6RBN-1 :EQNS.0,1,0,0,1,-40,0,1,0

:VE6RBN-1 :UNIT.Deg C,Deg C,Deg C

:VE6RBN-1 :PARM.House Temp,Outside Temp,Garage Temp

And I've setup the temperature beacon file to be sent out every 10 minutes.
T#199,23.3,31.2,15.5,0,0,00000000
The unique number (199 above) resets at midnight every day.
You can see the telemetry graphed here: VE6RBN-1 Telemetry
And you can see the raw packets here: VE6RBN-1 Raw Packets

Burnt Arduino

So what happens when you have a zener diode short out and rather than feed 5VDC to the Arduino Analogue Input, we feed 15VDC?

Yes, you guessed it! We let the magic smoke out!!!

If you look at the left side of the Arduino chip, you'll see a small bump, That bump is the melted plastic from the chip burning up!

Raspi & Gertduino UPS

I have purchased a couple of Arduino boards that are made specifically for the Raspberry Pi and they are named after their inventor Gert van Loo, Gertduino. The specs, software, and manual are available via this link.

It is a great platform to work on the inter-communication between the Raspi and the Arduino. I'll be using this combination to further develop my battery monitoring system for my Raspi UPS.
The Arduino will have a 3 level response:
      1)  My plan is to have my Raspi backup battery charged via the solar panels.
     2) The Arduino will monitor the battery voltage. If there is very little sun, or too much load, then the arduino can switch on the 110VAC battery charger to charge the batteries back up.
     3) The Arduino will continue to monitor the battery voltage, and if there is no sun AND no utility power, then the Arduino will safely shut down the Raspi if the voltage drops to a preset level. If the voltage continues to drop, the arduino will shut off as well.
     NOTE: The advantage of the Arduino is that it can safely recover from a power outage, where the Raspi may not. So the Arduino will power back up and when the battery voltage reaches a preset level, it will power up the Raspi.
     ARDUINO vs GERTDUINO: I like working with the Gertduino since it is mounted on the Raspi that it communicates with. However, I've been able to communicate with a regular Arduino Nano as well, so this would be the device I will use as my Battery Monitor, freeing the Raspi GPIO pins for other uses.

Raspi & APRX

For some reason when I completed the assembly of my RaspiTNC, I couldn't get it to run with APRX software, yet I was able to get it running on XASTIR. So I knew that my transmit and receive was working fine.... and had assumed (correctly) that I had probably made a mistake in my configuration file. I've gone back now and revisited the APRX Software page and re-read the APRX Manual. This time around I still had issues, but with the help of the APRX-Software Google Group I was able to find my configuration problem (I had left the - in my APRSIS password, so it wouldn't connect). Also I have to say that using my portable APRS setup = ASUS tablet running APRSDroid & Yaesu VX-6R & Mobilinkd TNC makes it easy to test out my iGate configurations.

Portable APRS Unit

Here is a pic of my Portable APRS unit that I've also used to test my Raspberry Pi TNC setup to ensure it is working OK:

You'll notice the high quality blue elastic that holds the Mobilinkd TNC to the back of the Yaesu VX-6R radio (grin). The cable was also purchased from Mobilinkd and I'm running APRSDroid on my ASUS Android tablet. The tablet is connected to the TNC via a Bluetooth link. You can see the map displayed on the tablet, however I usually run it in log mode to see  all of the traffic that it receives or transmits.