The Scientific Calculator That Doubles as a Secret Messenger
Turn this cheap scientific calculator into a discreet, pocket-sized AI terminal with a hidden OLED display and an ESP32.
It is well known that higher-end graphing calculators have a lot of power and can be hacked to do all sorts of things, like play video games or connect to the internet. But no one would ever suspect that the cheap scientific calculator modified by Instructables user karmou_44 could do anything like that. This Casio fx-991ES PLUS calculator was discreetly given a second display where the solar panel would normally be located. And this display is powered by a Wi-Fi-capable ESP32 microcontroller.
With these modifications, the calculator became a fully functional embedded system capable of connecting to Wi-Fi, sending and receiving messages, and querying AI services. The transformation is made possible by carefully integrating modern electronics into the calculator’s limited internal space.
Because the calculator itself has far more buttons than the ESP32 can directly handle, an MCP23017 I/O expander is used to add additional input/output pins. This allows the microcontroller to read button presses and interact with the calculator’s interface. Meanwhile, a tiny SSD1306 OLED display is connected via I2C, sharing the same communication lines as the expander, and serves as the output screen for messages and system feedback.
A rechargeable Li-Po battery is used to power the new hardware, along with a charging module for safe USB charging. Since the battery voltage fluctuates, a boost converter first raises it to 5V, and then a regulator steps it down to a stable 3.3V suitable for the electronics. A voltage divider allows the ESP32 to monitor battery levels so that the device can report its own power status.
The modified calculator can connect to a Telegram bot, enabling it to send and receive messages remotely. Users can type commands or questions on the calculator and receive responses directly on the OLED display. By integrating an AI API, the device can also process natural language queries, effectively turning the calculator into a pocket-sized AI terminal.
Despite all this added functionality, the external appearance remains largely unchanged. The components are carefully arranged and secured inside the original casing, preserving the calculator’s unassuming look.
If you would like to give your dumb calculator some real intelligence, be sure to check out the build guide for step-by-step instructions.
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