ARDF Timer / Controller

The ARDF controller was created after a request to be able to play random audiofiles for an ARDF transmitter, most existing designs were based on an 16F84, a somewhat aging design and better controllers are currently available. Also most controllers had a 5-10 mA current drain which can be improved, this design requires less than 400 uA.. To allow a very small controller footprint and flexible configuration the timer is not configured with (dip) switches but via a serial connection and a host PC. The memory option is optional and is only required for a wave file playback, all other options (CW, Single Tone, Tone Sequences and Audio Effects) do not require the I2C memory chip.

Short Overview of the ARDF Timer/Controller features


The Configuration Utility

The ARDF timer/controller is configured using the ARDFCF utility.
Click the image for a detailed explanation of all the options.



Click on the image for a large version.

Component List

Hier komt een korte beschrijving

1K 2X R2 R11  
2K2 3X R4 R7 R8  
4K7 3X R3 R5 R9  
10K 5X R1 R10 R12 R13 R18  
100K 1X R14  
33pF 2X C1 C2  
22nF 3X C9 C10 C11  
100nF 1X C9  
BC547 2X T1 T3 Any TUN will do
BC557 1X T2 or 2N5401 or BD136 (see text)
LP2950-5.0 1X IC1 any lowdrop
24C512P 1X IC2 optional, not required
PIC16F684 1X IC3  
32.786kHz 1X XTAL  
LED 1X LED any low current led

Short description

Pulling the reset line low wil reset the controller, if the SYNC line is held low during a reset the controller
will immediately start transmitting

This line is used to synchronize multiple transmitters, the line should be held low for at least 500 milliseconds and synchronisation starts when the line is released.

This line will enable the supply to the transmitter (supply side switching), R9 and Q1 determine the maximum current which can be switched. If the transmitter current is less than 100 mA a BC557/4k7 combination can be used. For up to 200 mA use a 2N5401/2k2 combination. Using a BD136/138/140 with a 470 ohm resistor will allow switching of currents in excess of 1A. The power is applied 100 milliseconds before the first transmission occurs, allowing the oscillator to stabilize.

Key is an active low signal (PTT line of transmitter). You can select KEY to remain low during the transmission (e.g. for AFSK CW) or actively switched with the CW modulation (for 80M fox transmitters)

The modulation is available on this pin, the maximum output is 2Vtt and with R6 the requested level is set.
Audio tones are created with a Software DDS and generate sinusodial signal.

The led shows the status of the system. The led will be on when the transmitter is active. When a SYNC signal is supplied
the led will also come on. During "inactive" periods the led will briefly flash every 2 seconds to show the system is running.
After a reset after a succesfull initialisation the led will flash briefly for 2 or 3 times to indicate the system is awaiting serial commands or a SYNC pulse.
3 flashes are given if external memory has been detected, 2 flashes if no memory had been found.

Two serial lines which are used to configure the timer/controller


A complete Transmitter/Timer project

Paul, PA3DFR, created a complete 2 Meter ARDF AM/FM transmitter with this timer which fits on a 64*73 mm PCB.
The schematic and PCB layout can be found here



2007-01-11 - V 0.0 Initial creation of this web page
2007-01-26 - V 0.8 Updated with new schematics/downloads
2007-02-02 - V 1.0 Added tone sequences
2007-02-05 - V 1.1 First complete version
2007-03-01 - Updated WEB page
2007-03-21 - V 1.3 Small mods, Calibration command added
2007-05-08 - V 2.0 Improved version with sequential transmission, recovery beacon, ringtones and much more
2010-06-01 - V 2.1 Added some additional CW characters, enlarged CW buffer from 15 to 31 chars


Windows configuration program (binary):

ARDF timer/controller code for 16F684 (binary V 2.0): aprs684_21.hex
ARDF timer/controller code for 16F684 (source V 2.0): aprs684_21.asm

Old Stuff (V2.0) aprs684_20.hex aprs684_20.asm

Audio sample files: Animal Collection Music Collection
RTTTL sample files: Ringtones

For questions of remarks: mail to PE1GRL