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    • #6129

        Hi everybody 😛

        Since we’re in the oscillator section, let’s have fun building other methods of sound creation.

        By going through the older Braun manuals  (Mini System), I found a neat little circuit : project 20 : Morse oscillator.

        This is the original circuit :

        Braun project 20 : morse generator

        Why not restyling this circuit to our modern variation with Silicon transistors ?

        So here I proudly present the modern variant with speaker output. When you build this circuit, make sure you are using the A3 metal base and put the blocks upper right. This is for forthcoming modifications. These will be published later on.

        Modern morse generator

        The principle remains the same. We have a 2 stage amplifier with a feedback loop consisting of the 0,1µF capacitor and switch.

        Also note the circuit around the transistor, driving the speaker.

        It differs from previous experiments by using a 220 Ohm resistor in series with the speaker transformer coil. We will discuss the circuit at the end of this post.

        In the meantime, why don’t you try to calculate the currents and voltages in this circuit and note them down in this forum ?

        To be continued …


      • #6132

          Hi Frank,

          As an amateur radio ham (WB2V), this circuit refresh is most welcome!  Thank you very much!

          As a future enhancement, may I suggest being able to change the pitch of the oscillator?

          Thanks Frank,


        • #6149

            Hi Michael,

            I’ve got some good news for you ! If you look at the circuit above, you’ll spot a 10K potentiometer at the top.

            This acts as a pitch control which brings us to the next topic : 2-tone oscillator.

            Here’s the circuit :

            2-tone generator

            We will add a few more blocks to the circuit and now we can generate a different tone by pressing the switch. You notice that we add a resistor by pressing the switch. By turning the potentiometer we can change the difference between the two tones and also the pitch.

            Careful readers might have noticed that we have here a so called VCO (Voltage Controlled Oscillator).

            By changing the DC bias of the first transistor, we’ll also change the amplification factor. This results in a change of pitch at the feedback circuit.

            Thanks to this fact and also the fast Lectron system we will create a lot of cool circuits.

            These will be published soon.

            Till then

            • This reply was modified 4 years, 2 months ago by Michael.
            • This reply was modified 4 years, 2 months ago by Michael. Reason: Changed font and size styling for easier reading
          • #6154

              Well that goes to show you Frank my level of electronics expertise!  I thought that the 10K pot was a volume control rather than a pitch control!

              Back to school for sure although with all your teaching moments, I am learning a lot!

              Thank you!

              • This reply was modified 4 years, 2 months ago by Michael.
              • This reply was modified 4 years, 2 months ago by Michael.
            • #6227

                The oscillation continues …

                So, we’re back with something really cool : an automatic 2-tone generator 😉

                For this, we use the oscillator circuit of above and we add an astable multivibrator !

                Now, the 2 tones are produced automatically. The potentiometer sets the depth of the 2 tones.

                Our Lectron start and expansion kit has all the parts needed and has even more parts to do some experiments as will published here.

                But let’s first build the 2-tone generator. Here’s the diagram :

                Auto 2-tone

                Now, let’s add some PWM (Pulse Width Modulation). With an extra potentiometer and a small modification to the circuit, we will add the possibility to change the length a pulse occurs. This control does not affect the speed of the astable multivibrator. Of course, we can use this kind of circuit to control the brightness of a light bulb. I will certainly publish this circuit later. In the meantime, can anyone  post a schematic here ?

                But first, let’s build the PWM for our tone generator. Here’s the diagram :

                tone PWM


                Some experimental tips :

                • change the two 10uF capacitors into one 0,1uF and the other one into a 0,47uF capacitor.
                • Replace the 0,1uF capacitor in the tone generator into 47nF.
                • Fiddle around with both potentiometers to find the “perfect” police siren.

                Tomorrow, we will be back with another cool circuit around this generator.

                Till then


              • #6231

                  Hi Frank,

                  Excellent work as always!

                  How are you producing the Lectron System blocks for your diagram?  Are you pulling them from the PDF?  Do you have a full set of the blocks that could be zipped up and made available for other (future) forum members?

                  Thanks so much,

                • #6267

                    Hello Michael,

                    Well, I’m using Splan from Abacom software.  Here’s the link

                    It’s a very easy but yet powerful tool for drawing schematics. Just pick your symbol and place it on a grid. It will snap to it’s position then.

                    This time, I’ve changed the background of the images to light grey to resemble the original circuits. Do you like it, or do you prefer the cool white ?

                    I have a (almost) full set of symbols for the Lectron system and I’m willing to share the library.

                    But let’s continue today with some new cool circuitry : a siren and a super siren !

                    These are build upon the principle of our VCO of above with some new circuitry.

                    Here’s the diagram of the siren. After building it, do not connect the ground block to the 100µF capacitor yet.

                    Now, press the switch. Do you hear the tonal quality of our oscillator ? It has a resonant filter circuit consisting of the speaker coil in parallel with a 0,47µF capacitor (can you spot it in the diagram ?) This produces a warm sound. The combination of R and is responsible for the frequency. Don’t forget to fiddle the potentiometer to find the perfect rise and fall of the siren.

                    Now, connect the ground block and press and release the switch …


                    But wait, there’s more ! Let’s build a super siren !

                    This siren works fully automatic and by fiddling the 3 potentiometers, you can create a lot of sound effects 😛

                    The circuit consists of the PWM astable multivibrator coupled to the siren circuit of above. The potentiometer at the right adjusts the influence of the 0,47µF capacitor to the circuit. It has also an effect on the AC current flowing through the transistors, thus also on the sound itself.

                    Super Siren

                    Lectron is a real cool tool, isn’t it ?

                    Have fun with the siren 🙂



                  • #6270

                      Hi Frank,

                      I really like the light grey especially as it respects the past and makes it easier to discern the blocks.

                      I use Microsoft Visio for repeating shapes and used Adobe Illustrator to create the Lectron System header graphic.

                      The original LectronRWO blocks were created with Corel Draw which is a vector format program.  Files can be exported in SVG, a standard web vector format.

                      I looked but did not find the graphic standards that your program supports.  It did mention a free viewer to view the proprietary graphics.  If it  can output SVG that’s great because browsers can support that format.  Obviously it supports output as jpg or png files.

                      Wow, if you have a complete library in which SVG versions can be produced, that would be great.  Please let me know what graphic formats your program supports.

                      Love the sirens!  If I were not getting ready for the Germany trip I would be trying these out for sure!  I am meeting with Dietrich Lubs during the trip (former deputy chief of design at Braun during Dieter Rams’ era there).  He will be fascinated to see what you have come up with!

                      Thanks again Frank, and best regards,

                    • #6271

                        Hi Frank,

                        Let me see if I can create the blocks in SVG from the CDR files.  This will be a lot easier to reproduce and create a block library that everyone can leverage.  I will keep you informed.  M.

                      • #6273

                          This is an SVG version of the Gene Block from model 1018. You can adjust this to your heart’s content to any size without any raster format artifacts!

                          • This reply was modified 4 years, 2 months ago by Michael.
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