K1EL CPO User manual

K1EL – CPO
Code Practice Oscillator
Kit Assembly & User Guide
Revision A.3
April 9, 2020
www.k1el.com

K1EL Morse Code Practice Oscillator CPO
CPO Datasheet – A.3 4/10/2020 Page 2
Features
•Keyed sine wave oscillator with wave shaping
•Volume control
•Frequency (pitch) adjustment control approx. 400 Hz to 1800 Hz
•RTTY test tone generation mode (2125/2295 Hz)
•Pushbuttons allow easy keying and FSK for testing purposes
•Internal low volume speaker for quiet practicing
•1/8” external speaker/headphone output jack with ½ watt output
•LED keying indicator lamp
•1/8” stereo key input jack (Key/FSK)
•1/8” audio line output jack adjustable 0 to 500 mV 5K impedance
•Mini-USB 5 volt power connector (power only, not data)
•Custom metal enclosure with stick on label
Description
The CPO is a versatile code practice oscillator with synthesized sine wave output and
adjustable frequency and volume controls. A 1/8” input jack is provided to key the
oscillator from practically any keyer or straight key. Note that the CPO does not have a
built in keyer, it is only a tone oscillator. A single chip microcontroller provides all of the
functionality of the CPO including sine wave generation. It is implemented in a Microchip
PIC12F1501 single chip microcontroller. An LM386 provides a higher drive level for an
internal speaker, external speaker, or headphones. A red keying pushbutton is provided
to manually key the oscillator for testing purposes. When the frequency (pitch) control is
set fully clockwise, RTTY test tone mode is enabled. When RTTY mode is active the
tone frequency is fixed at 2295 Hz. Asserting the FSK input (or pressing the black
pushbutton) will frequency shift the tone down to 2125 Hz.
Enclosure Label
Due to the extremely high cost of enclosure design and fabrication, we are changing the
way we use them. In the past we would offer a custom enclosure with silkscreen for
each product that we introduce. To continue this, we would have to double the price of
our products. So going forward, we are designing one enclosure for multiple products
and customizing them with a good quality stick-on product label. Following the trend in
pro-audio gear, we place this label on top of the unit. This has an advantage in that you
can see where rear connector plugs go without having to turn the unit around to look at
the rear panel.
I am mentioning this here because we want to be up front with this new process and not
surprise anyone.

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]

K1EL Morse Code Practice Oscillator CPO
CPO Datasheet – A.3 4/10/2020 Page 4
CPO Parts List
Ck Ref Des Qty Description
___ C1,C3,C4,C14 4 .01uF, ceramic capacitor (103)
___ C5,C8,C13 3 .0047uF ceramic capacitor (472)
___ C12 1 .047uF, ceramic capacitor (473)
___ C2,C7,C15,C16 4 .1uF, ceramic capacitor (blue) (104)
___ C10 1 1000uF,Capacitor Electrolytic
___ C6,C9 2 10uF,Capacitor Electrolytic
___ C11 1 100uF,Capacitor Electrolytic
___ R1 1 240 ohms 1/8W Red Yellow Brown
___ R8,R10 2 15K ohms 1/8W Brown Green Orange
___ R2,R3,R4,R5 4 10K ohms 1/8W Brown Black Orange
___ R9 1 12 ohms 1/8W Brown Red Black
___ RX2 1 5K Variable Trimmer Resistor (white)
___ D1 1 Red LED
___ S1 1 Black Push Button
___ S2 1 Red Push Button
___ U1 1 CPO PIC, PIC12F1501, 8 pin DIP
___ U2 1 LM386 8 pin DIP
___ SK1,SK2 2 8 pin DIP socket (for U1 and U2)
___ RX1,RX3 2 20K Potentiometer, right angle
___ J1,J4 2 1/8" SMT Jack
___ J2 1 1/8" SMT Jack w/switch
___ J3 1 Mini USB Jack, pre-soldered to PCB
___ SP1 1 Speaker
___ KN1, KN2 2 Control knob
___ PCB 1 CPO Printed Circuit Board
___ Enclosure 1 Metal Enclosure Top & Bottom
___ Feet 4 Press in rubber feet for enclosure base
___ Label 1 Product label 3.5” by 2”
___ HW1 5 4-40 x 3/16” silver pan head (pc board)
___ HW2 4 4-40 x 3/16” black pan head (cover)
DEPOPS
___ R6 1 100 ohms 1/4W - Not Included

K1EL Morse Code Practice Oscillator CPO
CPO Datasheet – A.3 4/10/2020 Page 5
CPO Assembly Instructions
Figure 2 shows the CPO board as shipped, note that the Mini USB connector is pre-
attached. The board is ready to build, please don’t clean it with solvent or an abrasive
pad. Be sure to use a good rosin core solder, avoid solder with acid or organic core.
Figure 2 – Board as shipped from K1EL
Start assembly with the resistors, their color codes are presented in the parts list but feel
free to verify them with an ohmmeter, the color bands on 1/8 watt resistors can be difficult to
read. Use Figure 4 on page 6 as a guide. As with all components to follow, insert the
component leads into the board and make sure the part is fully flush with the board. Then
bend the leads to hold the part in place before soldering. Neatly trim the leads.
Using a resistor lead scrap, install a wire jumper at location R7. Leave R6 unpopulated.
Insert and solder the two 8 pin DIP sockets at locations U1 and U2.
Now add the following capacitors:
C1,C3,C4,C14 > .01uF C5,C8,C13 > .0047uF C2,C7,C16,C15 > .1uF C12 >.047uF

K1EL Morse Code Practice Oscillator CPO
CPO Datasheet – A.3 4/10/2020 Page 6
For a better fit, straighten out the .0047 uF capacitor leads as shown in figure 3 below.
Figure 3 – C5, C8, C15 lead straightening
Figure 4 – First stage assembly complete

K1EL Morse Code Practice Oscillator CPO
CPO Datasheet – A.3 4/10/2020 Page 7
Install the two pushbutton switches, insure that the black switch goes in location S1 and the
red switch goes in location S2. Insure these are fully seated into the board before soldering.
It works best if you hold the switch in place while you solder one of the leads.
Install three electrolytic capacitors at C6, C9, and C11. Note that the plus side pad on the
board is square and this is where the longer of the two leads will go. As a double check,
note that the black band on the capacitor is oriented opposite of the + sign.
Install the two 20K control pots, RX1 and RX3. Be sure that these are fully seated to the
board before soldering. If you don’t do this right, the board won’t fit the enclosure. Also make
sure that all three signal leads go into their correct holes. If you push the pot firmly in place,
it will stay there while you solder.
Figure 5 – Second stage assembly complete
Now install three surface mount 1/8” jacks. Don’t let the term ‘surface mount’ scare you,
these are very easy to install. The light colored jack goes in the middle at location J2. There
are pilot holes in the board that accept the plastic nubs on each connector. Once in place
simply apply heat to the connector’s solder tab and the PCB pad and then flow some solder
over the tab. To insure mechanical strength, be sure to use enough solder to just cover the
tab but not more than that. Use Figure 6 as a guide. Keep in mind that these are plastic
connectors and can be damaged if you use too much heat or touch them with your iron.

K1EL Morse Code Practice Oscillator CPO
CPO Datasheet – A.3 4/10/2020 Page 8
Figure 6 – Surface mount jack installation
Install the 5K trimmer RX2, solder it so that it stands up straight, not leaning to one side.
It is easier if you solder the center pin first and then check the alignment, if you need to
move it, reflow the connection and nudge it in place. After soldering RX2 in place, set the
trimmer control knob to the halfway point it’s easiest to use a small screwdriver and turn the
knob until the flat side is at the top most position.
Install speaker SP1. There is a silver dot on the side of the speaker, orient this so that it
faces C12, this is not essential so don’t worry if you put it in backwards. Install the tall
electrolytic capacitor C10 the same way you installed C6, C9, and C11.
Figure 7 – Third stage assembly complete

K1EL Morse Code Practice Oscillator CPO
CPO Datasheet – A.3 4/10/2020 Page 9
Bend the LED leads as shown in figure 8. Make sure you bend the leads correctly. Note that
the flat side of the LED is facing away from the viewer. Populate the LED in the board so
that the longer lead goes into the hole closest to S2. Do not solder yet.
Figure 8 – LED Lead Preparation
Our goal is to install the LED in such a way that it will just poke out of the enclosure front
panel hole. It can’t sit too high, too far front, or too far back. The following two pictures on
page 10 illustrate the optimal LED placement.
Figure 9 – The LED lines up vertically with the pushbuttons
Figure 10 – The LED should extend from the PCB as shown

K1EL Morse Code Practice Oscillator CPO
CPO Datasheet – A.3 4/10/2020 Page 10
The CPO design has a provision for an on/off switch. It would be wired between PCB pads
S1 and S2. Since the kit does not include a switch, S1 and S2 must be connected together
with a resistor lead scrap as shown in figure 11 below. If desired, you can remove the
jumper and add a switch later. Note that you would have to put a hole in the enclosure to
add a power switch.
Figure 11 – DON’T FORGET TO JUMPER S1 to S2
Install the two 8 pin DIP ICs. The PIC12F1501 goes into position U1 and the LM386
goes into position U2. Please check to be sure you have pin 1 of the ICs in so that they
are next to the number 1 on the silkscreen. Pin one is indicated by a small round dimple
on the IC. The red arrows below point to pin 1 on each IC.
Figure 12 – U1 and U2 Pin 1 orientation
This concludes the assembly of the CPO board. With the exception of R6 should be no
missing parts. Be sure that all parts have been soldered without missing solder
connections or solder shorts.