This is a 1KHz audio oscillator using a Johnson Counter. ARTA software (http://www.artalabs.hr/) reports THD+Noise of 0.3%.

 

The Johnson Counter is very interesting. I believe I first ran into it in Don Lancaster’s classic 1977 CMOS Cookbook. My circuit uses an opamp summing junction to make the contribution of the resistor currents more accurate.

 

When you start from reset it clocks in ones until it is all ones. Then it clocks in zeros until it is all zeros. You get a 16-bit sequence from an 8-bit shift register. Then it repeats endlessly.

 

Since the sine wave is symmetrical you can choose the proper resistors to make an accurate offset sine wave that produces 16 samples. Notice that the resistors are symmetrical.

 

Each resistor adds a summing current at the proper time and then removes it at the proper time.

 

The accuracy of the sine wave depends on the accuracy of the resistors. Here I am using 1% resistors. I then use a first order filter followed by a second order filer to match to the frequency of the sine wave. With this I have measured a THD+Noise of 0.3% at 1 KHz.

 

There are two things to consider.

 

1. In order to reduce the THD+Noise further we would need to use 0.1% resistors or do more filtering. While 1% resistors are cheap, 0.1% resistors are expensive. It would be cheaper to use a microcontroller (such as the MSP430G2402) with a 12-bit SPI DAC (MCP4921).

 

2. Even at 0.3% THD+Noise we would need a tracking filter in order to get a wide range of frequencies.

 

But if you only need a narrow range of frequencies and 0.3% is good enough, then this is a low-cost way to do it.

 

There is a line output controlled by trim pot R20 and a microphone level output controlled by R23. The frequency is controlled by R4.

   

This is designed for 1KHz. Other frequencies can be produced if you change the values in the filters.

 

This board runs on +12VDC that regulates it down to +9VDC and uses an ICL7660 to produce -9V. The reason I took +12V down to +9V is because I want to be able to use the very cheap +12V switching power supplies from China via eBay. Some of these power supplies have 0.5V of hash on the output. Most of them are sold as LED power supplies (LEDs shouldn’t mind the hash) but some are sold as CCTV supplies. I bought two identical supplies (12V 1A) labeled for CCTV. With a load of 120 mA one had 50mV of hash (excellent) but the other had 200mV of hash (crap).

 

You can operate it from a 9V transistor battery by leaving out U1 (7809) and jumpering pins 1 and 3.

 

I recommend using IC sockets with machine-tooled pins and not the ones with leaf springs.


If you are not already a Maker (and you want to be one) see my tutorial on Making Things at www.jmargolin.com/making/jm_making.htm


JM

 

May 23,2019
250 viewsReport item
  • Comments(2)
  • Likes(2)
You can only upload 1 files in total. Each file cannot exceed 2MB. Supports JPG, JPEG, GIF, PNG, BMP
    View More
    VOTING 10 votes
    • Omer Faruk Ucar from TURKEY
      Founder of the project ‘Lezzetli Robot Tarifleri’ In the frame of this project he produces Turkish contents about electronics/software and serves it to people for free. He produced many jammer devices mostly drone dropper weapons while working in electronic defense industry. He gave lessons to teachers about software and electronics in a program which supported by the government. And now he is working as a hardware engineer on SCADA systems syber security.
      • 3
        design
      • 3
        usability
      • 3
        creativity
      • 3
        content
      3.00
    • Ilya Galkin from RUSSIAN FEDERATION, THE
      Senior hardware engineer
      • 8
        design
      • 8
        usability
      • 7
        creativity
      • 9
        content
      8.00
      • 7
        design
      • 6
        usability
      • 7
        creativity
      • 6
        content
      6.50
    • Catia Diaz from MEXICO
      Catia Diaz director of YouTube channel catykanal that was created to insentiate the taste for electronics with tutorials explained in a simple and fun way. Teacher with more than 3 years of experience in promoting the learning of electronics to children and young people.
      • 6
        design
      • 5
        usability
      • 5
        creativity
      • 2
        content
      4.50
    • Jiri Praus from CZECH REPUBLIC, THE
      If you got a low score from me, I don't think you fit for I can solder content. Sorry for that, at least I tried to rate your design. I am an artist. I design electronics and brass wire sculptures. www.jiripraus.cz
      • 6
        design
      • 1
        usability
      • 1
        creativity
      • 1
        content
      2.25
    • Oyvind Dahl from NORWAY
      NOTE: If you have a project that I don't think is for beginners (or I don't understand what it is/lacks documentation) - you'll automatically get a low score from me even though your project is really cool. Sorry! ABOUT: Author of Electronics For Kids. Creator of Ohmify.com and the electronics blog build-electronic-circuits.com.
      • 5
        design
      • 5
        usability
      • 5
        creativity
      • 1
        content
      4.00
    • Ever since I was a kid, I love tinkering with anything that involves energy from toys to cellphones. I love designing and creating projects that could be innovative with the use of electronics. I was also appointed team leader of the University of Sto. Tomas team for the Shell Eco-marathon Philippines Competition in 2018.
      • 6
        design
      • 6
        usability
      • 6
        creativity
      • 6
        content
      6.00
    • LUIS HARO from
      Youtuber & PCB Designer
      • 9
        design
      • 9
        usability
      • 9
        creativity
      • 9
        content
      9.00
    • J_RPM from SPAIN
      My name is José Ramón Pueyo, I live in Spain. For more than 40 years he has worked in the radio communication sector, mainly with RF equipment and developing control and monitoring systems.Five years ago I opened a channel on YouTube (J_RPM) in order to share some developments and divulge technical information.
      • 9
        design
      • 8
        usability
      • 9
        creativity
      • 9
        content
      8.75
    • www.cursoderobotica.com
      • 10
        design
      • 9
        usability
      • 9
        creativity
      • 9
        content
      9.25
    View More