Vectronics VEC-221K - Manual (Page 32)

VEC-221K Instruction Manual CW Memory Keyer Kit
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Circuit Description:
The VEC-221K features the powerful PIC16C72 microcontroller. This
integrated circuit contains the programming and basic power of a microprocessor
chip. CW speed is set via R6, a 10K-ohm potentiometer, that controls the
voltage input to pin 2 of U1 (PIC chip). Pin 2 is an analog-to-digital input for
the PIC processor. Programming subroutines scan the digitized setting of R6,
and adjust the speed accordingly.
Keyer paddle activation is also sensed by the PIC chip. All dot-and-dash
memories, iambic operations, and sidetone generation and sidetone frequency
are under the control of the PIC16C72 device.
The message memories and parameter settings are stored in the 24C04
EEPROM, a non-volatile memory IC that does not require battery backup to
preserve the recorded messages and settings.
Power to the PIC controller is regulated at 5 volts by 78L05 (U4), a low-power
5-Vdc regulator IC. The sidetone signal from the processor is filtered by R2-C6,
R3-C7, R4-C8 and L1-C16 to form a sinewave signal, which is amplified by U3,
a linear audio amplifier IC. U3 is powered directly from the 9-volt battery.
Transistor Q1 is a silicon-gate TMOS switching FET, and is used to key the
transmitter. The maximum FET ratings are 50 Vdc at 100 mA.
Specifications:
Voltage requirement ........................Internal 9-volt transistor battery
Keyer speed .....................................Typically 3 to 65 WPM
Sidetone level ..................................50 mW max., adjustable
Sidetone frequency ..........................701 Hz default, adjustable 300 to 1000 Hz.
Keying limit.....................................Positive keying. 50 volts at 100 mA max.
CW generation.................................Iambic A or B, Automatic or Semi-auto
Memory ...........................................Dot-Dash memory
Weight .............................................50% default, adjustable 25 to 75 percent
Message memories ..........................4 messages, about 120 characters each
SCHEMATIC