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

Based on a 16F684 PIC microcontroller.
Adjustable delay before the transmitter becomes active..
An "Autoshutdown" after a specified time to prevent battery drain.
"Recovery" mode where the transmitter becomes active again after a specified delay
The controller controls the power/ptt lines and also generates a selectable modulation signal.
Modulation can consist of the following:
- a fixed audiotone of any frequency
- an audio effect
- a sequence of audio tones
- a Nokia .RTTTL ringtone
- a CW signal (keyed or with audio tones)
- a .WAV audio sample (requires an I2C memory chip to store the waveform).
Options to send MO/MOE/MOI or random CW signals.
CW speed adjustable from 5 to 30 WPM.
Continuous transmission
Cycled transmission where the number of transmitters is selectable.
Sequential transmission where for each transmission cycle a different modulation can be selected
The interval time is selectable in 10 second units.
Very low power consumption: < 300uA when the transmitter is idle, < 5mA when the transmitter is active).
All options are configured via a Windows Setup program.
Multiple controllers can be synchronized via an external connection.

The Configuration Utility

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

Schematic

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

RESET
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

SYNC
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.

TX-POWER
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
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)

AUDIO
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.

LED
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.

PC RX and PC TX
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

Revisions:

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

Downloads:

Windows configuration program (binary): ardfcp21.zip

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) ardfcp20.zip aprs684_20.hex aprs684_20.asm

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