Voice-keyer with VELLEMAN module K8030

A voice-keyer is a device which records standard messages , and plays them back while keying the radio in TX. - this can be very useful and handy during contests! You can build a very performant voice-keyer on basis of the VELLEMAN K8030 module, with following features:

4 messages of 5 seconds each, or total of 20 seconds of one message record/playback .
message is saved in EEPROM, it is memorized for at least 100 yrs even if power is off.
power 10-15v or 6v DC, max 100 mA about
very good audio quality / fidelity
electret mic in with ALC for recording /// loudspeaker and 'line' out

Some hints and tips to build a voicekeyer:

	The VELLEMAN kit K8030 is based on a WINBOND chip ISD1400. Download more info about this chip from my site: Datasheet 1 -PDF document 270 kB Datasheet 2 -PDF document 220 kB This kit provides excellent audio, but is quite sensitive to presence of RF, and then will produce distortion. So you really need to take following precautions for good results: it must be housed in a metal enclosure (I made a box from double-sided PCB board) I power the keyer directly from my Icom IC-7400 mic plug, which provides +8v at 100 mA. All ground cable from the TRX mic plug (mic ground and 0v supply line) MUST be connected to single SK8 ('line') ground, and NOT to SK2. Using different grounds will cause 'ground loops' and signal distortion!
	If you power the module by external power, you must provide this through a choke coil to keep RF out. Wind a small bifilar choke coil on a ferrite rod (ex. on 5 x 30mm) , it is essential that both + and - lines are RF-decoupled. See schematic diagram As the ICOM mic plug will only provide +8v DC, I changed the regulator to 7805 to have stable +5v DC instead of 6v. I noticed some background 'oscillator' noise during playback, traced this as noise from the A/D digitiser. To avoid this, place a small electrolytic condensator (33 - 100湩/6v) directly between IC pins 28 (+) and 12 (-), under the PCB Signal for PTT can be taken from SK7 '+ speaker'. This signal can be used to drive an open collector NPN transistor (KEY signal) and a subminiature relay (which will change over the MIC and KEYER audio signals)
	Front panel view: a LED for Power indication, a pushbutton and LED for 'RECORD' and a pushbutton and LED for playback. I have wired the MIC plug receptacle so that the 'UP' and 'DOWN' buttons on the ICOM mic will trigger the 'playback' ... very handy ! The MIC is wired to the change-over relay and to the voice-keyer MIC input. the voice ker MIC output (SK8 line) is fed to a small 1 k trimmer and a 1 湩 capacitor (as the IC-7400 has +8v DC on the mic line)
	Back panel : the cable to TRX (use shielded cable and keep as short as possible) and put a ferrite choke the plug for external supply. This power will be supplied via a RF-choke (wound bifilar, + and -), where the (-) is supplied to the GND on SK8. Thanks to this ferrite choke, no interference / distortion, even with 1 kW PA!
	Bottom panel of the keyer. A 'speaker grille' for the monitor speaker, the volume can be adjusted by the trimmer. this can be useful if your TRX has no 'monitor' function... The MIC output volume can be adjusted by trimmer, accessible from a hole (left bottom). You must adjust this with the speech processor OFF, till you have full ALC deviation. Then, put the processor ON - you should have no distortion at all ! You could even add an 'automatic repeat' function with a 555 timer ...