# EEVblog 121GW

A rebuilt meter application runs on the real multimeter, including Bluetooth. Experimental firmware runs on the meter, including its Bluetooth functions.

Model: EEVblog 121GW

Maker: EEVblog

Category: cameras-sensors

Display type: Not applicable

Collections: None

Evidence: Source-reviewed creator project (not independent hands-on testing)

Sources reviewed: 2026-11-04

Added to directory: 2026-11-04

Development route: Rebuilt C firmware and bootloader

Setup: Advanced setup

## Overview

A rebuilt meter application runs on the real multimeter, including Bluetooth. Experimental firmware runs on the meter, including its Bluetooth functions.

Best for: Exact meter target. Open and rebuild a multimeter firmware.

Not for: A guaranteed plug-and-play recreation without the listed hardware revisions, accessories and software setup.

Where code runs: Experimental firmware runs on the meter, including its Bluetooth functions.

## Editorial popularity estimate

40/100. This is a subjective editorial estimate, NOT measured sales, traffic, quality, testing or customer reviews.

Conservative provisional ranking for a source-reviewed addition, not measured demand or product quality.

Inputs on a 1–5 scale: ecosystem 2 (50%), tutorial visibility 2 (30%), retail familiarity 2 (20%). Assessed 2026-11-04.

## Project ideas

- Open and rebuild a multimeter firmware

## What you need

- EEVblog 121GW

- Required: microSD card. The README documents the SD bootloader update path; match supported card formatting.

- Tool: microSD card reader. 

- Tool: Computer for setup. 

- Required: AA batteries. Manufacturer lists four AA cells; use fresh batteries for updating.

## Compatibility and cautions

- An enabling experiment, not a new everyday feature. Do not rely on modified firmware for safety-critical measurements.

- Source-reviewed, not independently hardware-tested. Confirm the model, revision and recovery process before changing device software.

## Buy

[Search Amazon (unverified)](https://www.amazon.com/s?k=EEVblog+121GW) — Search destination only; matching listing NOT verified

Search fallback only. No Amazon listing, stock, price or exact revision has been verified for this entry. Prefer the linked manufacturer or hardware source and check your region.

[View hardware source](https://eevblog.store/products/121gw-multimeter)

Exact product.   Stock and delivery region are not confirmed. Check exact model and bundle contents with the seller.

Affiliate link: no

## Creator projects and demos (source-reviewed; not independently hardware-tested)

## Setup and technical references

- [Open and rebuild a multimeter firmware](https://circuitdigest.com/news/eevblog-had-claude-code-rebuild-his-121gw-multimeter-firmware-in-c-overnight-and-it-works) — Circuit Digest / EEVblog; Build story

- [Open and rebuild a multimeter firmware — supporting source](https://github.com/EEVblog/121GW-Multimeter-Firmware-RE) — Circuit Digest / EEVblog; Project reference

- [EEVblog 121GW — Exact product](https://eevblog.store/products/121gw-multimeter) — EEVblog; Product page

## Planning notes (not a replacement for the original technical instructions)

1. **Check your model and revision**:  

2. **Read the creator’s setup**: An enabling experiment, not a new everyday feature. Do not rely on modified firmware for safety-critical measurements.

3. **Start with a reversible test**: Follow the linked project source before changing the device. Back up existing configuration, keep credentials private and stop if your hardware differs from the documented version.

## Coding-agent project brief

Help me plan open and rebuild a multimeter firmware using EEVblog 121GW. Read https://circuitdigest.com/news/eevblog-had-claude-code-rebuild-his-121gw-multimeter-firmware-in-c-overnight-and-it-works and its supporting sources first. Experimental firmware runs on the meter, including its Bluetooth functions. An enabling experiment, not a new everyday feature. Do not rely on modified firmware for safety-critical measurements. Confirm my exact hardware and required accessories, explain what is missing, and propose one reversible test. Ask before flashing firmware, changing privileged system settings or moving physical hardware.

## Common questions

### Where does my software run?

Experimental firmware runs on the meter, including its Bluetooth functions.

### What should I check before buying?

Exact product.   Stock and delivery region are not confirmed. Check exact model and bundle contents with the seller.

### What are the setup risks?

An enabling experiment, not a new everyday feature. Do not rely on modified firmware for safety-critical measurements.