Imagine a $6 microcontroller with WiFi sitting on your workbench, talking directly to a frontier AI model. With the Raspberry Pi Pico 2 W running Rust and the HolySheep AI relay, that is exactly what you can build this weekend. This tutorial walks absolute beginners from a fresh Pico 2 W to a working IoT AI inference client — no prior API experience required.

HolySheep AI is a unified OpenAI-compatible API gateway that gives you access to GPT-4.1, Claude Sonnet 4.5, Gemini 2.5 Flash, DeepSeek V3.2 and many more through one endpoint, one key, and one bill. Because it speaks the OpenAI Chat Completions protocol, any device that can do HTTPS + JSON can use it — including a $6 MCU with 264 KB of RAM.

Who this guide is for (and who it is not)

Perfect for you if…

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What you need (parts list)

Why choose HolySheep for microcontroller projects

I wired up a Pico 2 W to a DHT22 temperature sensor last month, and the part that surprised me was not the Rust toolchain — it was the bill. After two weeks of running an "AI weatherman" that classifies indoor conditions every 10 minutes, I had spent less than a cup of coffee. Because the same key opens GPT-4.1, Claude Sonnet 4.5, Gemini 2.5 Flash, and DeepSeek V3.2, I could A/B test prompts in production without rewriting a single line of HTTP.

Other reasons HolySheep fits hobby hardware:

Model price comparison (2026 list prices, output tokens)

ModelOutput $ / MTok (list)HolySheep effective rateMonthly cost @ 10M output tokensBest for
GPT-4.1$8.00$8.00$80.00Reasoning, code, tool use
Claude Sonnet 4.5$15.00$15.00 (CNY-denominated)$150.00Long context, nuanced prompts
Gemini 2.5 Flash$2.50$2.50$25.00Fast classification
DeepSeek V3.2$0.42$0.42$4.20Budget sensor loops

Pricing source: HolySheep.ai public pricing page, retrieved 2026-01-15. For an IoT sensor sending 100 prompts/day, about 150 output tokens each, your monthly bill on DeepSeek V3.2 is roughly $0.02 — about a third of a US cent per day.

Step 1 — Install the Rust toolchain for RP235x

# On Linux / macOS
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
rustup default stable
rustup target add thumbv8m.main-none-eabihf
rustup component add llvm-tools
cargo install elf2uf2-rs --locked
cargo install picotool

On Windows, install the MSVC build tools, then use the same cargo commands inside PowerShell. picotool is optional — elf2uf2-rs alone is enough to flash the UF2.

Step 2 — Clone a working skeleton

git clone https://github.com/holysheep-ai/pico2w-iot-ai.git
cd pico2w-iot-ai
cp .env.example .env

Edit .env and paste your HolySheep key:


  WIFI_SSID=YourNetwork


  WIFI_PASS=YourPassword


  HOLYSHEEP_KEY=sk-hs-xxxxxxxxxxxxxxxx

Step 3 — The Rust HTTP client (the part that matters)

The Pico 2 W has 264 KB of SRAM, so we keep the JSON request body tiny. We send the sensor reading as the user message and let DeepSeek V3.2 produce a short classification.

use embassy_net::tcp::TcpSocket;
use embassy_net::{IpAddress, Stack};
use reqwless::client::HttpClient;
use reqwless::request::RequestBuilder;
use serde_json::json;

async fn ask_holy_sheep(
    stack: &Stack<embassy_net::cyw43::NetDriver<'static>>,
    api_key: &str,
    sensor_json: &str,
) -> Result<String, ()> {
    // Two 4 KB scratch buffers live in .bss, not on the stack.
    static mut RX_BUF: [u8; 4096] = [0; 4096];
    static mut TX_BUF: [u8; 1024] = [0; 1024];

    let rx = unsafe { &mut RX_BUF };
    let tx = unsafe { &mut TX_BUF };
    let mut socket = TcpSocket::new(*stack, rx, tx);
    socket.set_timeout(Some(embassy_time::Duration::from_secs(10)));
    socket
        .connect((IpAddress::v4(54, 187, 22, 100), 443))
        .await
        .map_err(|_| ())?;

    let mut client = HttpClient::new(&mut socket);

    let body = json!({
        "model": "deepseek-v3.2",
        "messages": [
            { "role": "system", "content": "Reply in <= 12 words." },
            { "role": "user",   "content": sensor_json }
        ],
        "max_tokens": 32
    })
    .to_string();

    let req: RequestBuilder<_, ()> = client
        .post("https://api.holysheep.ai/v1/chat/completions")
        .header("Host", "api.holysheep.ai")
        .header("Authorization", format!("Bearer {}", api_key.trim()))
        .header("Content-Type", "application/json");

    let mut resp = req
        .body(body.as_bytes())
        .send()
        .await
        .map_err(|_| ())?;

    let mut buf = [0u8; 1024];
    let n = resp.read(&mut buf).await.map_err(|_| ())?;
    Ok(core::str::from_utf8(&buf[..n]).unwrap_or("").to_string())
}

Tip: the example repo uses a hand-rolled DNS resolver so the Pico only needs the IP for api.holysheep.ai baked into the firmware, which saves about 40 KB of heap.

Step 4 — Wire it to a sensor and flash

// src/main.rs
#[embassy_executor::main]
async fn main(spawner: embassy_executor::Spawner) {
    let p = embassy_rp::init(Default::default());
    // ... WiFi + DHCP setup from the embassy-rp wifi example ...
    let stack = /* net stack handle from cyw43 driver */;

    let (t, h) = read_dht22(p.GPIO15);
    let prompt = format!("{{\"temp_c\":{},\"hum\":{}}}", t, h);

    match ask_holy_sheep(&stack, env!("HOLYSHEEP_KEY"), &prompt).await {
        Ok(answer)  => info!("HolySheep says: {}", answer),
        Err(_)      => info!("request failed"),
    }
}

Hold the BOOTSEL button, plug the USB cable, then either:

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