Have you ever wished for a little desk companion—something with the tactile charm of a retro game character that could chat with you, keep track of your desk timers, or talk you through a tricky bug—without a camera staring at you all day?

That question sparked DinoDesk AI: our LEGO Dino AI Companion Robot.

I and my colleague Shama set out to build a smart, low-power desk robot that combines the nostalgia of 8-bit audio-visuals and LEGO Technic mechanics with a modern Hybrid LLM Switching Architecture (Local ↔ Cloud). By pairing a Raspberry Pi on the desk with a local PC gateway running Gemma 4 alongside Gemini Flash, we created a companion that offers 100% visual privacy (no camera), instantaneous zero-cost local chat, and deep cloud reasoning on demand.

Here is the full behind-the-scenes story of how we designed, wired, and programmed DinoDesk AI from the ground up.

1. The Hybrid Brain: Local Gemma 4 ↔ Cloud Gemini

One of the biggest dilemmas when building an AI hardware companion is choosing where the brain lives. If everything runs in the cloud, every casual "What time is it?" costs API tokens, adds network latency, and sends your voice data over the internet. On the other hand, if you strictly limit yourself to a small on-device model, the robot struggles the moment you ask it to create a new feature in your gigantic codebase, or explain a complex topic.

So we decided to build a Hybrid LLM Architecture, with a Unified LLM Gateway (Router) hosted on the user's main PC. The Raspberry Pi on your desk sends identical OpenAI-compatible requests over Wi-Fi regardless of which engine is active:

 ┌─────────────────────────────────────────────────┐
 │           [ Main PC / Local Gateway ]           │
 │                                                 │
 │   ┌─────────────────────────────────────────┐   │
 │   │      Dynamic Model Router / Switch      │   │
 │   └────────────────────┬────────────────────┘   │
 │                        │                        │
 │     ┌──────────────────┴──────────────────┐     │
 │     v                                     v     │
 │  [ LOCAL ENGINE ]              [ CLOUD ENGINE ] │
 │  LM Studio / Gemma 4           Gemini Flash /   │
 │  (Zero Latency, Private)       Gemini Live      │
 └────────────────────────┬────────────────────────┘
                          │
                          │ Wi-Fi (Unified OpenAI-Compatible Stream)
                          v
 ┌─────────────────────────────────────────────────┐
 │           [ DinoDesk AI (RPi) ]                 │
 │  - Pirate Audio LCD & I2S Beep Speaker          │
 │  - Push Button & Optional Sensors               │
 └─────────────────────────────────────────────────┘

Three Modes of Intelligence

When Auto-Hybrid Mode escalates a question to the cloud, the robot's indicator temporarily shifts from 🟢 steady green to 🟡 steady gold for the duration of the response, then returns to green—so you always know at a glance which brain is answering.

2. Hardware & Tactile Mechanics: LEGO Meets Pirate Audio

We wanted DinoDesk AI to feel like a physical toy rather than a cold smart speaker. Instead of 3D-printing a sealed plastic shell, we built the body out of basic LEGO bricks and Technic lever mechanisms so anyone can customize or repair it.

Core Bill of Materials (BOM)

1. Main Controller: Raspberry Pi + 32GB MicroSD
2. Display & Audio Shield: Pimoroni Pirate Audio Speaker (1.3" 240×240 ST7789 IPS LCD + I2S 1W Speaker + 4 tactile buttons)
3. The Red Button: A mini push button switch that gives you a satisfying tactile click to start or stop voice capture
4. Audio Input: Compact USB Mini Microphone
5. Motion System: Motors driving Neck movements and Tail wagging

Before building the full body, I first prototyped the logic using a Raspberry Pi and a simple LEGO set.

Physical Button Controls

Even with voice and sensor triggers, dedicated hardware buttons feel good for instant physical control:

• Button A (GPIO 5) — Cancel / Mute: Immediately stops the active response stream, silences audio, and returns the robot to Idle.
• Button B (GPIO 6) — Home Re-Center: Resets all servos to their neutral center position without interrupting the current state.
• Button X (GPIO 16) — Expression & Engine Switch: Single-click cycles facial expressions manually; double-click toggles Local ↔ Cloud Mode.
• Button Y (GPIO 24) — Tail Test & Volume: Single-press fires a tail-wagging sequence to verify mechanical alignment; a 2-second long-press cycles beep volume (Low → Medium → High → Mute).

3. Bringing the Dino to Life: The 5-State Finite State Machine

A companion robot only feels alive when its eyes, voice, and body move together. We designed a 5-stage Finite State Machine (FSM) that coordinates the 240×240 LCD eye expressions, 8-bit beeps, and motor movements:

┌──────────┐  button     ┌───────────┐   release   ┌──────────┐   stream   ┌──────────┐
│ Sleeping │──────────>  │   Idle    │────────────>│Listening │─────────>  │ Thinking │
└──────────┘  (wake)     └───────────┘   (trigger) └──────────┘  (send)    └──────────┘
                             ^                                                  │
                             │              ┌──────────┐                        │
                             └──────────────│ Speaking │<───────────────────────┘
                               (done)       └──────────┘       (tokens arrive)

Building DinoDesk AI reminded us that AI doesn't have to stay locked inside a browser tab or a cloud data center. When you give an open model like Gemma 4 a pair of pixel eyes, an 8-bit voice, a wiggling LEGO tail, and the ability to call on Gemini when things get heavy, your desk suddenly feels a whole lot more lively. 🦖✨

It's still a work in progress and not quite perfect yet, but I'll be back soon with fully implemented voice chat capabilities! Until then, please enjoy the fun little 8-bit sound effects every time you press the button. Beep-Boop!

Clone the repo here : https://github.com/google-gemma/dinodesk-ai-companion/

And drop a comment to share what you're planning to create.