Step-by-step Fox Transmitter Controller

Based on the Montreal Foxbox by François Tremblay VE2JX and Jacques Brodeur VE2EMM.
By Charles Scharlau, NZØI


Here's some information to make fox hunting more fun when you're the one hiding the transmitters. It's always more fun if you can use an automated fox transmitter that will operate unattended. I recommend using a battery-powered transmitter (an old crystal controlled HT will do) and a Montreal Foxhunt Controller. The controller can be built for less than $20; this includes the printed circuit board, and all the parts to put on it. Details of the Montreal Fox Controller are available at the sites listed below. Included is some special software for making the foxhunt controller do some new tricks. Getting your PIC programmed, if you don't have a friend with a programmer, is only a little tricky. But there's LOTS of information available on the Internet that will help you program your PIC 16F84.

Step 1: Learn more about the Fox Controller

The Montreal Fox Controller, featured in 73 Magazine's "Homing In" column for April 1998, is an inexpensive and easy-to-build controller that can turn most any handy-talky into an international-style fox transmitter. Jacques and François do an excellent job of describing their Montreal Foxbox, including a schematic, on their website at <>. You should definitely make their web site your first destination if you are considering building the fox transmitter controller described below.

Equally informative is the web page which Joe Moell, KØOV, has dedicated to the Montreal Controller. Make it your second destination: <>.

Step 2: Parts

Here is a list of all the parts needed to build a complete Montreal Fox Controller. The list is divided into two parts. List I contains those parts that are not likely to be found in the average junk box. These parts you will probably need to mail order.

List I: Uncommon Parts
Description Digi-Key Part# Qty Needed
Printed Circuit Board n/a 1
PIC Processor* PIC16F84-10/P-ND 1
18-pin DIP socket AE7218-ND 1
DIP switch (9 pos) CKN3008-ND 1
4.19 MHz Crystal CTX007-ND 1
10K Pot 3386P-103-ND 1
5V Regulator LM78L05ACZ-ND 1
22 pF low-temp-coef 5% cap P4841-ND 2

List II contains those parts that are fairly common. You might want to try to scrounge the parts listed in List II before resorting to buying them new.

List II: Parts to scrounge
Description Digi-Key Part# Qty Needed
10K resistor   2
4.7K resistor   1
1K resistor   1
47K resistor   1
100K resistor   1
6.8K resistor   2
0.1 µF cap   5
0.01 µF cap   2
SPST mom. cont.   2
1N4148 diode   5
2N2222 transistor PN2222ADICT-ND 2
LED 67-1106-ND 1

Other parts you may want or need: battery, battery holder and connector, wires & connectors to connect the controller to your HT, chassis box, PCB mounting hardware.

Step 3: Programming the PIC

Jacques provides some sources of PIC information (i.e., Microchip Corporation) and at least one supplier for PIC programmers: <>

An inexpensive way to program the PIC16F84 is to modify a Montreal Fox Controller circuit board so that it can program the PIC in circuit. The so-called No Parts PIC Programmer can be wired directly to the modified Fox Controller circuit board allowing the PIC to be programmed and then tested without having to remove the PIC from its socket. This is especially handy if you ever write software for the PIC, or make modifications to the Montreal Fox Controller software. You'll be able to quickly make changes to the software, assemble it, program it into the PIC, and then test it.

Many electronics projects have been designed using the PIC16F84 processor. Having a way to program them will open up a world of new project possibilities. So, if you enjoy building small electronics projects, the afternoon spent turning a Montreal Fox Controller into an in-circuit PIC programmer is time well spent.

Step 4: New Software for the Montreal Controller

If you are planning to modify Jacque's original software for this project, and you are a native English speaker, you might appreciate this English translation of the Montreal Fox Controller assembly code:
If you have an interest in making the Montreal Controller use shorter transmit intervals, then this new version of the Fox Controller for ROCA-style hunts might be of interest: