You can make a handheld virtual pet with a microcontroller, a small display, a few buttons, a buzzer and a protected rechargeable battery. An ESP32 is a flexible choice for a color-screen build; an Arduino Nano suits a simpler monochrome version. Start by prototyping the electronics, then program the pet’s needs and actions before designing a case.
Choose a controller and display
The board determines which displays and libraries are practical, how much room you have for graphics and game logic, and how much wiring your build needs. Two demonstrated approaches are an ESP32-based monochrome build and a color-screen build using an ESP32-C3; an Arduino Nano is another option for a simpler pet.
| Build choice | Display example | Best fit |
|---|---|---|
| ESP32 reference build | 0.96-inch SSD1306 I2C OLED, 128×64 pixels | Compact monochrome graphics and a straightforward wiring reference. ArduinoGotchi project |
| ESP32-C3 color build | 1.69-inch ST7789, 240×280 pixels; the project notes ST7735 modules as an alternative when reducing memory demands | Color graphics, animations and sprite customization. ESP32-C3 project |
| Arduino Nano build | Display details are not stated on the project page | A simpler monochrome-oriented alternative. Arduino Nano project |
Match the display’s interface and library to the exact board and module you buy. I2C uses fewer signal wires than SPI, while a color display can require more memory and rendering work than a small monochrome screen.
Gather the parts
For a basic handheld prototype, plan on these components:
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- An ESP32 development board or Arduino Nano.
- A compatible small OLED or TFT display.
- Three or four tactile buttons for pet actions and menus.
- A piezo buzzer for sound feedback.
- A protected single-cell 3.7 V LiPo battery, a suitable 1S charging circuit and a regulator or boost stage appropriate to your board and display.
- Jumper wires or a small prototyping board, plus a USB cable for programming and charging as supported by your chosen hardware.
The ArduinoGotchi reference explicitly lists the protected battery, charger and power-conversion components alongside the display, buttons and buzzer. Review its parts and wiring reference before buying: board voltage and display requirements affect the power circuit you need.
Wire buttons, display and sound
Connect the buttons
Use one GPIO input per button. A common arrangement uses the microcontroller’s internal pull-up resistor: configure each input as INPUT_PULLUP, wire the button between that pin and ground, and treat a LOW reading as pressed and HIGH as unpressed. This logic is easy to reverse accidentally in code, so test each control before assigning actions.
The firmware walkthrough demonstrates this button-input pattern alongside the pet model and display logic. See the firmware tutorial.
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Connect the screen and buzzer
Wire an I2C OLED to the board’s I2C pins, or connect an SPI TFT to the specific pins required by its module and library. Pin assignments vary by board and display, so follow the matching project’s wiring rather than copying a pin map from another build. Connect the piezo buzzer to a suitable GPIO output and use short tones to confirm actions or signal a need.
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Prove the circuit before making it portable
First power the build from USB and check the display, every button and the buzzer. Add the battery and charging circuit only after the board-and-display combination works. Confirm the charger is designed for a single-cell LiPo and that the regulator or boost stage supplies the voltages your components require; do not connect a bare LiPo directly to a board or display unless its specifications explicitly allow it.
Program the pet as a state machine
A virtual pet is a small embedded program that stores needs, accepts actions, updates those needs over time and redraws the screen. Separate those jobs so that a button press does not freeze the clock or animation.
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Define the pet’s state
Start with fields such as hunger, happiness, energy, age and the time of the last update. Set sensible bounds for each meter so a value cannot grow indefinitely or fall below zero. Pick the meaning of each scale—for example, whether a larger hunger value means more hungry or better fed—and use it consistently in the rules and graphics.
Update needs on a timer
Use elapsed time to change the pet’s meters at intervals rather than making them drop once per screen redraw. The main loop can check for elapsed time, apply the need changes, read controls, trigger any animation or sound, and render the latest state. Timer-based updates keep the pet’s behavior predictable even when a display refresh takes longer than expected.
Map controls to actions
Give each button a clear purpose, such as feed, play, clean or sleep. Actions should change the relevant state: feeding can reduce hunger, play can raise happiness while using energy, and sleep can restore energy. Add limits and feedback so the user can tell when an action has an effect.
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Draw the pet and its status
Render a pet sprite together with readable status bars or icons. For a small monochrome OLED, keep shapes bold and labels short; on a color TFT, use color to distinguish moods or needs without relying on color alone. The firmware tutorial organizes the work around a pet model, update logic, button input, sprites and display rendering.
Add animation, sound and progression
Once the basic loop works, add idle animation, short sound effects, mini-games or changes in appearance as the pet ages or reaches milestones. Keep animation timing separate from need timers so a lively screen does not accelerate hunger. The ESP32-C3 project exposes animation timing, mini-game behavior and sprite arrays for customization. Explore its display and behavior example.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Build an enclosure after prototyping
Keep the electronics on a breadboard or temporary plate while you settle button placement, screen visibility and battery position. A case is not required to prove the pet works; postponing it makes wiring and code changes easier.
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For a printed enclosure, the ArduinoGotchi design uses separate top, bottom, spacer and battery-holder pieces fastened with M3 screws and nuts. A printing service is an alternative if you do not own a printer. The Arduino Nano project recommends PETG for its enclosure. See the enclosure project and the Nano build for their respective designs.
Flash, test and refine
- Install the board support. In Arduino IDE, add support for the exact ESP32 or Nano-compatible board you selected, or use the project’s documented PlatformIO workflow.
- Install matching libraries. Use the display and input libraries required by your chosen module and project. A library for one display controller may not work with another.
- Connect over USB and select the board and port. Compile and resolve any board, library or pin-definition errors before uploading.
- Upload with the device still open. Confirm that the screen starts, buttons register with the intended pressed logic, and the buzzer responds.
- Exercise the pet’s states. Test feeding, play, cleaning and sleep, then let timed needs change and verify the bars and animations reflect the underlying state.
- Check battery operation and charging. Verify the board remains stable on battery power and that the selected charger behaves as specified before closing the case.
- Close the enclosure only after the fit is proven. Make sure buttons move freely, the screen is visible, and the battery and wiring cannot be pinched by the shell.
The ArduinoGotchi and firmware projects describe Arduino IDE or PlatformIO upload workflows. Battery-runtime figures and a reliable total build cost are not established for these examples, so plan to measure runtime on your own hardware rather than assume a particular result.
Build from parts or start with a kit?
Building from separate parts offers more control over the board, display, enclosure and game rules, and it makes the electronics and firmware easier to adapt. It also leaves you to check compatibility and assemble the power system. Arduino’s CircuitPet is a kit-oriented alternative described as “Build & Code Your Own Handheld Virtual Pet!” Its listing includes a board, acrylic casing, buttons, RGB LED, buzzer, LiPo battery and display board, but it was marked sold out when checked; availability may change.
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