K1EL
Morse Code Practice Oscillator
CPO
CPO Datasheet – A.3
4/10/2020
Page
3
CPO Functional Block Diagram
Figure 1 is a block diagram of the CPO. The CPO PIC accepts input from the
pushbuttons and keying input jack. When keyed, the CPO generates a PWM encoded
sine output that passes through a low pass filter and to both an audio line output
connector and the input of the LM368 audio amplifier. The AF amp drives the external
speaker output connector. When nothing plugged into the speaker connector, the
amplified audio is switched the internal speaker. The Pitch control is read by an analog
to digital converter in the PIC which governs the frequency of the audio tone generated.
Power for the CPO is provided by a Mini USB connector, most any USB power supply
can be used to power the CPO, which draws a small amount of current.
CPO
Controller
PIC
&
Low Pass
Filter
Pushbuttons
Internal
Speaker
Speaker
Output Jack
3.5mm
1/8"
Audio Line
Out Jack
5 volts
3.5mm
1/8"
CPO Block Diagram
K1EL Rev C
2/6/20
FSK
Key
Pitch
Volume
miniUSB
Power
Connector
Keying/FSK
Input
3.5mm
1/8"
LM386
AF AMP
Figure 1 – CPO Block Diagram
CPO KIT Construction
The MTB keyer kit consists of a single board with all through-hole components for easy
assembly. It’s a good idea to read through all of the assembly instructions before
starting. Please be sure to follow the steps in the order presented for best results. Even
if you are an experienced builder, we highly recommend reviewing the appendices A, B,
and C at the end of this document for helpful assembly hints. Bottom line, don’t start
assembly late at night when you are tired and in a hurry, it will just end badly.
Using the parts list as a guide, identify all of the components in the kit before starting.
Check off each item in the list. If you are missing a part or are having trouble identifying
something, email us and we will help: [email protected]