NT7S Code Practice Oscillator

NT7S Code Practice Oscillator - In Altoids Tin

Here it is, a completed version of the simple discrete component code practice oscillator that I promised. I tweaked the circuit just a little bit and made a Manhattan layout that will enable the CPO, a 9 volt battery, and all of the required controls to fit into a standard sized Altoids tin. This CPO produces a nice sine wave at about 600 Hz, unlike many of the other CPOs that output a buzzy square wave tone. There are no exotic parts used in this project, only a couple of generic NPN transistors, a handful of common resistors and capacitors, and a trim pot. The output level is sufficent for headphone use, although it will not blow your eardrums out, even at full volume. If you need to use a speaker with this oscillator, just plug it into a set of amplified speakers, like those used for a computer. This project would also make a good oscillator for CW practice on a VHF/UHF FM repeater. The volume control should allow you to adjust the output level to one that is appropriate for the microphone jack of a FM rig.

NT7S Code Practice Oscillator - Tin Open
Inside view of the CPO

I’ve attached a PDF schematic and layout diagram below. I haven’t created any build instructions, but it should be an easy build for anyone who has any experience with Manhattan construction. Let me know if you plan on using this design for a group build to help people learn CW, I might be able to work with you to create such a document. Print out the layout diagram at 100% scale, and you should be able to use it to size your copper clad board and mark the locations of your pads. I hope this is helpful to you and can help you to introduce new operators to CW.


16 thoughts on “NT7S Code Practice Oscillator

  1. Hey, a little rusty on my manhattan construction could you possibly send me a step by step construction. Thanks, would greatly appreciate it.

  2. Your site popped up when I googled: practice code oscillator. I have a renewed interest in electronics from days of old and intend to share this intrest with my grandson so I thought we’d get our tech lic. together and even learn code together.(like the original hams did it :>). Please make sure I have access to your data base I see a wealth of knowledge there and I’d enjoy shareing it with my grandson.

  3. @Robert Mendel

    Thanks for taking the time to comment! I’m really happy to hear about you and your grandson working together to get your Tech licences. Even better that you guys are going to learn code! It’s encouraging that there are still folks who want to do it the “old-fashioned” way.

    Check back in when you get your licences and also let me know if you build the CPO and if it helps you at all. One of the thinks I hope to do with my new company is to come out with a kit or two for the beginner such as you and your grandson. Check back in a half-year or so and hopefully I’ll have something out by then.

    Jason NT7S

  4. I have been a CW op for 32 years and I am very picky about the quality of sidetone. I just built this circuit last night and was very very pleased! I am gonna add an amp circuit tonight, probably using an LM386 or equivilant. and put it in a nice case with a quality speaker, can’t wait to hear it’s sound when that is complete. Thank you very much for posting, I have your site bookmarked!

    73, Tom K7TPD

  5. Done! Added an op amp circuit (LM386) and an 8 ohm speaker, assembled into a nice plastic case and it sounds amazing. I’m gonna turn down the sidetone on my HF rig and keyers and use this thing exclusivley. I turned the trimmer pot (of the twin-t circuit) way down and I use the op amp circuit to adjust the volume. Thanks again for posting!!

    Tom K7TPD

  6. @Tom Dean K7TPD
    Awesome! Glad you like it! It’s true that nothing beats a clean sine wave sidetone, especially when compared to some of the near square wave tones you see on the simpler CW kits. Thanks for being a reader and bookmarking the blog!

    Jason NT7S

  7. You have done a great job– I have held a ham license for over 50 years and it is rewarding to see some one is carrying on the real true aspect of amateur radio- It all started as a do it yourself Hobby Thanks to folks like you it still is — Thank you– Eddie

  8. did you get around to creating the instruction kit? Just wondering…I was a ham 35 years ago…made it to general class…but have been out of it since then.

    My 8 year old daughter and I just finished reading a kids spy novel that included morse code as part of the setting. She’s very keen to learn. I have my fathers key from when he was a kid as a family heirloom of sorts…would love to build this design for my daughter to use in learning code.

    I could probably pull it off just from the diagram, but if you have any instructions would be most appreciated.

    Many thanks for posting it!


  9. Hi Jim,

    I’m sorry, unfortunately I have not done the instructions. I will fully admit that one of my annoying weaknesses is the intention to take on far too many tasks than I can reasonably handle. Right now I’m knee-deep on trying to make the final revisions to my CC-Series design so that I can get it to market (only about a year late).

    It’s very cool that your daughter is interested in the Code and it would be great to take advantage of that interest. I wish I had some instructions to help you. I can’t promise anything, but I’ll see if I can’t squeeze in some time to write up a simple bit of documentation for the oscillator.

    If you decide to try to tackle it before I can write up docs, please feel free to ask for help any time you might need it.

    Thanks and good luck!
    Jason NT7S

  10. Jason,
    Thanks for posting your CPO plans. I’m learning CW and I built one from your plan and it actually worked! My chagrin was no refrlection on your design, but directed towards my building skills – hi hi.

  11. Hi, very nice project. I wonder if it’s possible to modify the frequency of the sine wave (would like it around 700 Hz).

    Anyway, great little project.



  12. This looks like a fun project.
    does this oscillator work with a paddle or just a straight key?
    I am looking for one that will work with an iambic paddle.
    Either way I am going to build one.

  13. Matt,
    The oscillator is intended for straight key use, but there’s no reason why you couldn’t connect a keyer to it in order to use it with a paddle.

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