K1EL
Morse Code Practice Oscillator
CPO
CPO Datasheet – A.3
4/10/2020
Page
12
CPO Kit Checkout
If you have a voltmeter get it out and get ready to measure voltage. Plug a USB cable
into the CPO and plug the other end into a USB charger or USB power supply. Measure
the voltage between the jumper at R7 and the ground pads next to J1. You should see
something very close to 5 volts. Now set the volume and pitch controls to mid range.
Press the red pushbutton and you should hear a tone from the built in speaker, it won’t
be super loud. You will also see the LED light up with the tone. Now adjust the pitch
control while holding down the red button and you should hear the audio frequency
change. If you advance the pitch control fully clockwise you will select RTTY test tone
mode. Now when you press the red pushbutton you will hear a tone of approx 2125 Hz
and if you press both pushbuttons the frequency will shift approximately 170 Hz.
If you have a set of stereo headphones, adjust the volume to minimum and then plug
them into the external speaker jack. Press the red pushbutton and advance the audio
level to a comfortable listening level. Note that the internal speaker will now be off. If you
have an external speaker, you can test that the same as headphones. Note the speaker
must have a stereo connector with the speaker connected between tip and ring.
The audio line output can be fed into an amplifier to generate even more volume. The
CPO’s internal trimmer can be adjusted to provide a convenient level.
Troubleshooting
The CPO is a fairly simple kit and if you take your time it should work the first time it’s
powered up. Here are a few areas to check out if you are having trouble.
If you don’t see 5V, make sure the S1 to S2 jumper is in place. Is your USB power
source working properly? Do you have a good USB cable? Are the electrolytic caps in
correctly with black stripe away from the + sign?
If you have power but no tone, make sure that the two ICs are in the right place,
positioned correctly, and without bent or missing pins. Is the speaker soldered in
correctly? Is the jumper at R7 installed? Look for missed solder connections on the
control pots or other components on the board. Is there output on the AF line out
connector? If so that narrows it down to the AF amplifier section. Does external speaker
connection work? If so, that means points to the internal speaker connections.
Finishing Touches
Now that everything is working, it’s time to finish CPO assembly. Push on the volume
and pitch control knobs. You will have to align the flat of the shaft with the flat of the
knob. Now attach the top cover. The easiest way to do this is to fold the top in position
using the USB connector as an anchor point. Once the connector lines up with its hole
you can fold the top down easily. Attach the top with four black 4-40 screws (HW2).