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.

Raspberry Pi TNC & APRS

I've finally got my RaspiTNC up and running on my Raspberry Pi. It is hard to tell from the screen, but I'm running Xastir APRS software. The APRS (Automatic Packet Reporting System) is a wonderful project led by Bob Bruninga, WB4APR, APRS. Essentially APRS is digital communications for Amateur Radio operators. Here is my home iGate station with Xastir running on the screen:

Here is a closer look at the radio and Rasperberry Pi & TNC:

The radio is showing APRS, which is the memory name for 144.390MHz, the North American APRS frequency.

A closer look at the brains of the system:

The red board is the RaspiTNC, & the green board just below is the Raspberry Pi. Just below that in the somewhat clear case is an external USB hub to power everything and below that is an 8 port switch to hook everything up. 

**** Please ignore the very, very poor job of soldering the capacitor & resistor to the 9 pin SubD connector on the RaspiTNC. This is what happens when you are in a hurry……

However I am happy to report that the TNC receives data packets via RF and transmits them to aprs.fi, and also receives packets from the internet and sends them out via RF.

You can see the APRS J-Pole antenna that I used in a post about 4 weeks ago. it is omnidirectional to provide fairly even coverage around Irricana.

If you want to see where my station is from anywhere in the world, click over to aprs.fi and track call sign VE6RBN-1 which will zoom right into my rig show here.

Raspi Block Heater Control

Well, I have a Raspberry Pi controlling a 5VDC relay, which in turn controls a 120VAC Relay which can then turn my vehicles block heater on & off. For those of you who don't live in the colder Northern climates… a block heater is an electric element that is positioned within the water jacket of your automobile engine. When the temperatures drop below -10C to -20C, the engine is cold, the engine oil is much thicker, the battery loses some of its capacity, and starting can be difficult. When we talk of plugging our cars in, we're referring to plugging the block heater in to provide heating (much like a hot water kettle) for the engine so that it will be much easier to start at those frigid temperatures. My first attempt:

You can see the Raspberry Pi in the upper left hand corner, and the 2x5VDC relays (blue) just above it.  The 5VDC relays can safely be driven from the Raspi's GPIO pins and they can safely trigger a 120VAC relay that will power the block heaters. You can see the 2 x 120VAC relays on the DIN rail just above the 3 white/grey circuit breakers. There is an advantage to using these relays (commonly known as ice cube relays, because they are about that size), and that is 1) there is an indicator light to tell me if it is powered on and 2) there is a manual lever that I can move to manually activate the relay for troubleshooting purposes. Also, if for some reason, my Raspberry Pi was not running, I could manually activate the relays to power the block heaters continuously to ensure my vehicles start in the morning. There are 2 sets of relays to power 2 different block heaters in 2 vehicles.

The only problem with the above setup is that if there is a power failure during the evening, the Raspi's SD card may become corrupted and not restart when power is applied. I find this happens on occasion and I assume it is because the SD card is being written to when the power fails.

So version 2 includes my thoughts on a UPS that I've talked about here on this blog. I've installed a power supply (upper right) and 6 x AA batteries in a holder mountain just above the Wall Adapter on the right.

Now the 12VDC wall adapter powers the power supply (small circuit board to the upper right of the DIN rail) through a 1N4007 diode. Also the 6 x AA (6 x 1.5VDC = 9VDC) batteries are tied to the power supply as well through a 1N4007 diode. Normally when the wall adapter is working, it's diode is forward biased and the power supply is supplied by the wall adapter. Should the House Power fail, the voltage will drop until it reaches 8.3VDC (9VDC from the batteries - 0.7VDC to forward bias that diode). At this point the Raspberry Pi power supply will be powered from the batteries.

Our power outages occur fairly frequently (several times a month), however they are short lived. I am hoping this battery pack will last me thru the winter…..grin.

I'm running the WebIOPi software which allows me to have the block heaters turn on and off via preset times, as well as through a webpage on my smart phone or tablet. Thanks got to Eric Ptak (trouch) who is the author of this wonderful software, WebIOPi

Raspberry Pi UPS

I've had an ongoing issue with my Raspberry Pi's corrupting the SD card if the power failed during a write cycle, at least that's my assumption. On occasion, after a power outage, I cannot access the Raspberry Pi and have to reboot it. By watching the terminal display, it often indicated a kernel panic and I know that I have to re-write the SD card. About 10% of the time I cannot and have to throw the SD card out.

Most often, it seems that the power outages last for a brief period of time. So I went looking for a short term backup solution. My first thought was to go with rechargeable batteries, and I may still follow this route, but for now I've settled upon standard alkaline batteries to provide my short term coverage.

I've come up with the following circuit to prevent power loss to my raspberry pi's. I use a 12VDC wall adapter together with 6x1.5VDC (AA) batteries. Both feed the 10-30VDC > 5VDC power supply through diodes. My reasoning is that as long as the wall adapter is working, it will supply the voltage & current to the power supply, since the battery diode is reverse biased. If I lose utility power, the wall adapter voltage drops to zero, and then the battery diode becomes forward biased and supplies the voltage and  current to the power supply.

I have sourced the power supplies & wall adapters from China. 6 cell AA battery holder from my local electronics store and using 1N4007 Diodes to provide the isolation.