Hidden Transmitter Hunting - Fox or Bunny Transmitter Controller

 The KR7W Hutch of Hidden Transmitter Hunt Bunnies are becoming aged.  The old timer bunnies are made from Icom handy talkies from approx. 1982, use a Ham Gadgets Repeater controller circa 2005, and contain a 5-pound Sealed Lead Acid battery.  The battery seems to double in weight for each year I grow older.   Enter some fairly new technology – that’s not just for newly licensed hams.

Since College Days- KR7W's workshop has been
dubbed "Acme" after the many projects built. Where some projects
worked as well as Roadrunner catching gizmos that the Coyote
used to entertain us with.

At Amazon.com, Baofeng UV5R handy talkies are currently priced at approx $20 and their Extra Strength 3800 m/A batteries are the same price.  For about $40 (plus ancillary parts) a long-lasting hidden transmitter can be built.  But, how to control it?  Or... how to key the FM signal plus the station ID for a certain time, then shut down for a certain time, and then start back up, over and over again?     Arduino Nano (3 for $20 at Amazon), plus inexpensive miscellaneous parts to the rescue.

 This blog article hopefully reveals my so far successful creation of a reliable, powerful, Hidden Transmitter or Fox or Bunny that will run for the duration of the hunt.

 The Baofeng part is easy– insert the charged 3800 a/H battery, set the frequency, set Low Power, let the LOCK.   The Arduino controller was challenging.  I do not know the C++ Programming language to create a program of my own.  Persistent Google searches found a Fox Controller Project that uses an Arduino Nano that has simple wiring and a well-documented sketch (the program file) that helped me to figure out what to change to fit my Fox Hunt needs. 

The Block Diagram - Schematic basically explained:    The Arduino is programmed to operate Push To Talk and play a user defined Morse Code sequence for 33 seconds.  Pin D12 outputs +5V when this happens.  +5V is divided by R1 and R2 to place approx. 2.5V on the G of the 2N7000 transistor.  A GND then appears on the D lead– which is PTT toward the Baofeng.   PTT is wired to the 3.5mm plug Sleeve lead.

 The Morse Audio appears at Pin D13.  The Audio Level is a 5V square wave that is divided (attenuated) by R3 and R4 to emulate the level of a Baofeng Speaker Mic.   Capacitor C1 blocks the DC voltage from the Baofeng mic lead.  Transmit audio is applied to the Ring lead of the 3.5mm Plug.  Note:  Pin D13 has a board mounted LED connected across it.  When the Morse Message is playing- the LED flashes along.  

9V from the battery passes through a small toggle switch that turns the Arduino controller ON-OFF.  The 9V source connects to the Arduino at the V-in pin.    GND for the Baofeng’s PTT and Mic Audio In is delivered via the sleeve of the 2.5mm Plug.

Many people have told me that the hardest part of programming Arduinos is ‘Getting the Sketch into the Arduino’.    I encourage you to watch some Youtube videos like:  Arduino Nano how to load a Sketch - YouTube... 

Or read about it at:  Getting Started with Arduino products | Arduino   Ask around at your Radio Club. The sketch I used is here:  Auto-Keyer for Radio "Fox Hunting" | Arduino Project Hub  

I’d like to tell you that customizing the Arduino to meet your Fox/Bunny Hunt needs is EASY– but, nah.  However, it’s not too difficult if the notes in the sketch are carefully read.

An example is Changing the Morse Message.  Note:  If the line of programming in the sketch is preceded by a double slash // – what follows is the explanation the programmer left for you.  Also known as 'comments' or 'commented out'- which has no effect on the Adruino Programing.  

 // the loop routine runs over and over again forever:

void loop() {

  digitalWrite(relay, HIGH);   // turn the relay on (HIGH is the voltage level)

  delay(1000);                 // wait for a second, 1000mS

   SendText("A A A A A A A A A A A DE KR7W"); 

   delay(1000);                 // wait for one second

   //SendText("KR7W FOX HUNT");// alternate text to use

   //tone(TonePin, frequency);    // send 7 sec tone

  //delay(7000);

  //noTone(TonePin);

   //delay(1000);                 // 1 seconds transmit w/o tone

 

Find the line that begins with: SendText(  The text between the quote marks is what will be sent in Morse Code.  The amount of text, between the quote marks, determines the amount of time Push To Talk will be operated.   I added this amount of As to make the PTT stay operated for 33 seconds.  Experiment to meet your needs.  Change the sketch then reload it into the Arduino.

 Here,  digitalWrite(relay, LOW);  turns OFF Push to Talk.  Then delay(cycleDelay); makes the Arduino wait for 15 seconds (defined elsewhere).  It performs this command twice for a wait time, with PTT non-operated, for 30 seconds.

 digitalWrite(relay, LOW);    // turn the relay off by making the voltage LOW

   delay(cycleDelay);           // wait for cycle time (because the largest value is 16383)

  delay(cycleDelay);           // wait for cycle time 

 

The following photos show how I went about creating a Fox / Bunny Controller that works for me and just might provide some ideas for your project.

 Electronic parts are shown on the schematic-block diagram, Fig 1, above.

 A Mint Tin ended up being the perfect size for the Arduino and the 9V battery.  My non odorous mint tins, as well as the Arduino, battery connector, small toggle switch, 2N7000 transistor, Audio Plugs, hook up wire, solder, soldering tips, resistors and capacitors conveniently came from Astronaut Bezo’s Amazon dot com.

 

(Fig. A) A piece of Printed Circuit Board with Dremel cuts creates Manhattan style solder pads for wires to attach– as well as a ground plane to easily GND a component or wire connection.    

(Fig. B) A piece of 5mm scrap plywood was cut into 2 pieces and glued together to become the 'platform'.  The smaller plywood piece became the divider to hold the battery in place.  The Arduino is glued to the platform with E6000 hobby cement.

Hot Glue would work just as well.

The wire shown- passes through small holes drilled through the plywood and printed circuit board.  The wire ends are soldered to the PCB Ground Plane.  The intent is to Bond the PCB GND Plane to the Mint Tin.   This may not be needed- but did it, as it was easy.

(Fig. C) The notch Dremel carved into the plywood platform holds it in place under the switch.  At some point the platform will need to be removed for Arduino reprogramming.  Accidental Engineering provides the platform to easily slide out toward the bottom of the tin without removing the battery for access to the USB port.

 

Got Questions?  Email me.                                                

  As Always– thanks for reading this far.  30, 73, Happy Trails, KR7W