Audio frequency generator - IPRS Baneasa - Prospect 8108

Audio frequency generator - IPRS Baneasa - Prospect 8108

Reading time: 3 minute

What does the project present?

An audio frequency generator is an electronic assembly that must not be missing from the workshop or laboratory of any amateur electronics technician.

Such a generator can be used in the most diverse electronic applications: debugging, generation of onomatopoeias, checking of audio frequency amplifiers, electronic sirens, etc.

How does the circuit work?

This vintage DIY electronic kit is an audio frequency generator made with the CBD 400E integrated circuit (SN7400). With the help of three YES-NO gates and several resistors and capacitors, a frequency of approximately 1 KHz is generated.

The signal generated by the assembly is reproduced with the help of a headset of impedance of approximately 50 Ohm. It is recommended to power the entire assembly from a 4.5V battery or from a stabilized 5 volt source.

Technical characteristics of the assembly

  • Vcc power supply = 5V (battery or DC voltage source)
  • Telephone headset: impedance Z = 50 Ohm

List of required components (with recent equivalents):

  • CI - integrated circuit B400E or SN7400
  • C1, C2 - capacitors - 0.22 uF (min. 100V)
  • C3 - capacitor - 47 uF (min. 12V)
  • R1, R2 - 2.2 KOhm resistors (min. 0.5W)
  • 50 Ohm headset (small Chinese speaker recovered from a portable radio or a walkman headset)
  • Printed wiring or breadboard test board
  • Tin or connecting threads

Download the original IPRS leaflet Baneasa 8108

For a better understanding of the operation of the circuit we will need electronic scheme presented below:

In order to carry out this project in our own laboratory, we will also need printed wiring PCB layout From lower:

Many of you are probably wondering how this DIY electronic kit was packaged or distributed. Below I have attached a picture with packaged product (new). Thanks sir. Marius Balauta!

Also, in order to better understand the operation of the presented assembly, I also attached catalog data for CI CBD 400E:

I have attached below an image with assembled assembly. The speaker is not part of the kit.



  1. It was nice to be able to connect to the antenna input of a black and white TV. The "surprise" was that at one point some black and white bars appeared in the manual search. That kilohertz had thousands of harmonics and that's what happens. I was instructed not to connect in vain through the TV, not to remove the cover…. Crazy times.

  2. I made it too. And playing with a diode between different points, my TV went crazy, the image waved and the sound was uncontrollable! I was having fun with friends with the toy in my pocket!

  3. I built this one and modified some capacitors and resistors for other frequencies. I even came across him the other day.

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