YO4HFU
DIGITAL AUDIO RECORDER...CQ CQ CQ CONTEST





This device can record 6 audio tracks. It is useful for SSB contest CQ. Can replace an ISDxxxx recorder chip.
The card memory is an SD or micro SD + adapter (easy soldering). 2GB are enough for 24 hours of recording. Capacity size is selected by DIP switches located on the PCB.
For best signal/noise ratio, ATMEGA A/D convertor need aprox. 4,5Vpp audio signal, without clipping. I used an TL072 preamplifier for electret microphone. Gain is around of 90 times.
When the operator need to bypass the recorder in order to start the QSO, some relays are used to bypass the recorder. Atmega32 can internal bypass the audio signal by A/D back to D/A conversion (pin 29 not used). I don't recommend this option, the quality of microphone signal is affected by sampling rate and low pass filter response. Better is to use a relay or CMOS switch 4016, 4066. Recording VU-meter circuit is not used, LY2BOK PCB can be simplified and redisgned for better ground plane and decoupling.
In order to repeat the audio track, an 74HC4538 monostable was added. The delay time can be adjusted and repeat function can be switched OFF/ON. DC "click" noise present at the begin of play sequence was rejected ~0,5sec by a muting circuit. LM386 is audio monitor during play period.
In the box recorder was included a "digital modes" interface and a Beep/K tone generator built with 4017 counter. Rx-Tx tone generator is useful during QSB and QRM.

Record procedure

- open "ON-OFF Repeat" switch
- select desired track location using "Track Selection" rotary switch (1 to 6)
- press "REC" push buton
- press "PLAY" push buton. In this way, 4538 generates a short pulse and Track uC pin (22...27) is selected. Recording is started and "REC LED" lites.
- start to speak in front of the microphone
- press again "PLAY" to stop recording, "REC LED" goes to OFF


Play procedure

- open "ON-OFF Repeat" switch
- select desired track location using "Track Selection" rotary switch (1 to 6)
- press "PLAY" push buton. In this way, 4538 generates a short pulse and Track uC pin (22...27) is selected.
- audio track stored on SD card can be heard by monitor speaker. Adjust "Level Monitor" for best audition. "PLAY LED" is on during play sequence.

If "Bypass OFF LED" is lite, the PTT output is activated and transceiver is ready to transmit. "Local PTT LED" is on during radio transmitting.
Press again "Bypass" push button if you need only audio play, without transceiver usage.


Normal operation during CQ Contest
- "Bypass OFF LED" need to be on. Press again "Bypass" push button if is necessary.
- close "ON-OFF Repeat" switch if you need to repeat the CQ. If the switch is open, CQ track will be sent only one time.
- select desired CQ track using "Track Selection" rotary switch (1 to 6)
- press "PLAY" push button. Transmitter PTT is enabled and audio signal is injected in the transceiver. Simultaneous, monitor speaker can be used to check yours CQ.
- when CQ track is ended, the transceiver is switched back to RX. After "delay" time, the TX process is automatically repeated. Adjust "Repeat Delay" if you need more time for RX break.
- When a station reply to CQ, immediately press "Bypass" and start to use the transceiver microphone like for a normal QSO. Repeat function will be automatically disabled during recorder bypass (RLY D).



Original Article: RADIO 7/2010, RA9YTJ
Modified project: LY2BOKĀ & LY3BD


PHOTO GALLERY (DIGITAL RECORDER + K TONE + PC INTERFACE)
Front Panel
General view
Digital Board
K Tone, Repeat Board
Switch Board (4013 Relays), Audio preampl.
PC Audio Interface

- Updated 2017
Block Diagram
Atmega 32 - Schematic (revision)
Beep/K Roger Generator - Schematic
Repeat Unit - Schematic
Flip-Flop Bypass - Schematic
PC Interface for Digital Modes - Schematic

PCB(original)
(rar file)
Atmega32 Firmware
(zip file)

Pony Prog Bytes Configuration

 


 
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