Circuit Description - Ramsey Electronics BULLSHOOTER ENDLESS LOOP BS2C Assembly And Instruction Manual

BS2C CIRCUIT DESCRIPTION
We will go through the BS2C section by section, but most circuitry that used to
be in separate circuits in the BS1 has been fully integrated into the BS2C main
chip. For example, you can switch between the microphone and line inputs
digitally so you can select them using the front panel switches. The part also
contains a speaker power amplifier so we no longer need a separate IC for this.
The BS2C power supply: The power supply is fairly basic in that we only need a
single voltage to run the entire kit. The trend these days is to run things from
lower voltages for faster operation and less power requirements, so all of the
parts in the BS2C run from 3.3V. VR1 is a low-dropout 1.5 Amp regulator,
though we will hopefully never pull that much current with the BS2C during
operation. This part "smoothes" out the incoming, usually noisy wall wart power
supply voltage into a nice, clean, predictable voltage to supply all of the other
components.
The BS2C "brains": The brain of this kit is a nice Motorola microcontroller, the
MC68HRC908JK1. This part contains 1.5K of ROM for all the memory required
for the program and space saving settings. Compare that to your PC memory
space! This part is used to interpret the key presses, and then act on them by
controlling the voice recorder IC, U3. It also controls the LED display and
monitors for "End of Message" indications from U2, the voice recorder, to know
when to replay messages.
The BS2C sound recorder IC: This part is a fully integrated component, loaded
with options for switching audio, mixing audio, adjusting gains, changing
BS2 • 5