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Author Topic: PiFox script - turn a $35 raspberry pi into an easy to use foxhunt transmitter  (Read 30689 times)

Posts: 3

« on: October 14, 2014, 03:19:45 PM »

I just recently finished this script that turns the raspberry pi into an easy to use and configure fox hunt transmitter.  Please have a look at it and give me feedback.  It has been tested to work on a raspberry pi model b and it uses nbfm to transmit through one of pi's gpio outputs.  It should work on the b+ and I imagine even the model a. I chose gpio pins that are the same on all models.

Please see above link for more information.

Any feedback or improvements or bug reports are welcome.  Future plans are to combine it with an usb sdr dvb dongle to control it via dtmf codes.  Still waiting on hardware to start that project.  Let me know how it works for you.  A low pass filter is required but that is about it.  Optionally if not interested in building a lpf and actually by default you can use the audio out from the pi and vox on a handheld radio as a fox transmitter. Lots of options and configurations are available. Please see the readme section 5 under installation configuring pifox for different setup ideas.
« Last Edit: October 14, 2014, 03:26:54 PM by KM4EFP » Logged

Posts: 3

« Reply #1 on: October 14, 2014, 04:44:31 PM »

Here is an excerpt from read me file for deploying the pifox in several modes in case you do not feel like clicking the link and scrolling through read me.

When using HAM frequencies a license is required by the FCC. If using nbfm and your pi's GPIO4(pin7) as a transmitter a low pass or band pass filter is required. For this reason vox is used by default with an external handheld radio's mic connected to Pi's audio out usually by use of an appropriately sized audio cable. This way you set the vox on your radio to detect Pi's audio out and your radio transmits the message. This is the easiest way to deploy the fox legally. To utilize GPIO 4 and use the Pi by itself as a transmitter you must set vox to 0 in settings. In this case no handheld radio is required, you simply add a wire to pin 7 on your Pi and feed into a low pass or bandpass filter for the chosen frequency and from there to an antenna.

See for an easy to build low pass filter on the 2m band.

pifox can be ran in several modes both assisted requiring a connection to the pi to run the script and unassisted. When in unassisted mode we call it autofox. When autofox is enabled it bypasses all menus and goes straight into transmitting. To disable autofox to edit settings or for whatever reason run "sudo ./ autofoxoff". You can set autofox in settings to 1 to automatically run pifox with your configured settings. With just this setting enabled it still requires you to log into your pi and run the script which may not be convenient in the field. To solve this problem I added a menu item to setup pifox to run when your pi boots up or is powered on. Simply select the run at boot menu option to have pifox run when power is connected to the pi. To stop the transmission when your pi boots up run "sudo ./ killfox" and to remove from startup select the menu option remove from boot. This may still not be ideal and I thought of this instance too and wrote a script to only transmit when a switch is flipped or an on/off button is on. For this instance you would set foxbutton to 1. This uses GPIO 23(pin 16) connected to a switch on a pullup resistor to transmit your fox. Please refer to the included schematic if you need help with this. My foxbox has a pi powered by a 6000mah usb power bank inside a 30 caliber ammo can and is running pifox and starts automatically when the pi is powered on and waits for a switch to be flipped before it starts transmitting as in the last example. In my opinion this is the ideal method of deploying the fox in the field. It requires no user input and is easy for anyone to deploy with just the flip of a switch.

Posts: 3

« Reply #2 on: November 06, 2014, 11:05:17 AM »

Project is also on hackaday.  Please check it out there to see a youtube video of it in action and pictures.  Login and skull it if you like it.
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