This ESP32 Interactive voice response system project uses the GeoLinker GL868 board with an ESP32-S3 and SIM868 GSM module to create a fully standalone IVRS system. Instead of using apps or internet services, the user simply makes a phone call to the system and controls connected devices using keypad inputs.
The idea is simple but very practical. Once the call is answered, the system plays voice instructions and waits for DTMF keypad commands. Based on the pressed key, the ESP32 turns devices ON or OFF instantly.
How the IVRS System Works
The system operates completely over the GSM network. When someone calls the SIM868 module, the ESP32 automatically answers the call after a predefined number of rings.
For example:
- Pressing “1” turns ON Output 1
- Pressing “2” turns OFF Output 1
- Pressing “3” turns ON Output 2
- Pressing “4” turns OFF Output 2
The system also plays confirmation audio like “Output 1 turned ON,” making the interaction feel natural and user-friendly.
Main Hardware Used
The project uses only a few core components:
- GeoLinker GL868 Board
- MCP602 Op-Amp
- Resistors and Capacitors
- SIM868 GSM Module
- Relay Outputs
The GeoLinker board combines ESP32-S3 processing, GSM communication, GPS support, and power management into one compact platform, making the overall setup much simpler.
Audio Playback System
One interesting part of this project is the audio playback design. Since the ESP32 outputs digital sigma-delta audio, the signal contains switching noise and cannot directly drive the SIM868 microphone input.
To solve this, the project uses:
- A low-pass filter
- MCP6002 op-amp stage
- Voltage divider network
This converts the ESP32 output into clean analog audio suitable for voice playback during calls.
All audio files are stored inside ESP32 memory using LittleFS.
Why This Project Is Useful
Unlike cloud-based automation systems, this setup works entirely through GSM communication. That means:
- No internet required
- No mobile app required
- Works in remote areas
- Can be controlled from any basic phone
This makes it useful for:
- Home automation
- Agricultural motor control
- Industrial switching systems
- Security applications
- Remote monitoring setups
Expandability
The project is designed to scale easily. Additional GPIO outputs can be added simply by assigning new keypad buttons and connecting more relays.
For example:
- Key “5” → Output 3 ON
- Key “6” → Output 3 OFF
The IVRS menu audio can also be updated with new voice instructions.
This ESP32 Interactive Voice Response System is a great example of practical automation without depending on the internet. By combining GSM communication, DTMF decoding, audio playback, and GPIO control, the project creates a reliable remote-control solution that works almost anywhere with cellular coverage.
If you enjoy embedded systems, automation, or GSM-based projects, this is a very interesting build to explore.
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