PBX Communications Device for Preventing Phone Fraud for Senior Citizens

Consumer electronics
Embedded hardware development


Every year, thousands of people lose money to telephone scams. The majority of these victims are elderly. Crimes against the elderly continue to skyrocket each year. One way to protect people from telephone scammers is by using telecom technology.


To build a device that blocks fraudulent calls, Johannes Kinscher, a private entrepreneur, decided to use the capabilities of a Private Branch Exchange (PBX) system.

PBX is a private telephone network often used within an organization. The idea of this phone system is that it allows the use of different communication channels like Voice over IP, ISDN or analog for letting users communicate internally within their company as well as externally with the outside world. With PBX you can transfer calls, use voicemail and interactive voice menus, record calls, and make call queues. These features of the private telephone network make it a great solution for a fraud-blocking device.

Johannes Kinscher was looking for experienced hardware engineers with specialized expertise in PBX programming.


Integra Sources was chosen to design PCB for a special device that helps avoid fraudulent calls. Our hardware development team implemented full-cycle printed circuit board design services from schematic design to prototyping assembly to testing.

Technologies Used

STM32F415 with Cortex-M4 core was used as MCU in this project.
We built a high-efficiency 2-stage step-up converter from 5V to 150V for a ring signal.
FreeRTOS was used for firmware development.
The device has several connectors and LEDs.
Altium Designer IDE was used for Schematics and PCB design.
Microsoft Visual Studio with Visual GDB plugin was used for firmware implementation.
The firmware was implemented using C/C++.
SPI NOR flash and SD Card is used to store audio data.
ADC and DAC were used to capture and generate voice signals to the telephone line.
For Ethernet communication, we used Wiznet W5500 chip.
To decode caller ID, a special FSK demodulator IC was used.


Our client received a ready-for-manufacturing PCB for the telecommunications device used to protect senior citizens from phone scams. The device works as a mini-PBX but with one subscriber line. It connects between PBX and a user phone and fully emulates a PBX port.  

The device is small in size and powered by a conventional 5V micro USB adapter used to charge mobile phones. It provides access to Ethernet LAN through an embedded port, has 2M bytes Flash storage, and an external SD card connector. We installed a high-performance STM32F415 microcontroller on the PCB to provide the ability for data encryption/decryption on a hardware level.

"The part we like most about Integra was their intensive experience in the development space. That fact alone enabled us to predict and avoid a great number of costly unexpected situations that are quite common for such complex projects."

Johannes Kinscher, founder

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Scope of work

Schematics design

PCB design

Case design

Generation files for the manufacturer

Ordering the components and PCB manufacturing

Prototyping assembly

Hardware testing


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