Multimeter Card

The Multimeter Card is a Tool Card from HW Media Lab LLC that fits a full multimeter into a Framework Expansion Card form factor¹. It is designed to work with the DockFrame modular USB-C hub or plugged directly into any USB-C host¹². It measures DC/AC voltage, DC current, resistance, capacitance, and inductance with galvanic isolation between the measurement domain and the host¹³.

In Development

The Multimeter Card is in pre-production as of 2026. A Crowd Supply campaign is planned. All hardware and software will be open-sourced after the campaign closes¹³.

Design

The card uses a two-domain PCB layout with galvanic isolation between the host and measurement sides¹:

• Host side: USB-C plug with ESD protection (TPD1E05U06DPY), VBUS TVS (SMAJ7.0CA), and input fuse
• Isolation barrier: ADuM4160BRWZ (5 kV digital USB isolator) for data; SN6501 push-pull driver + Wuerth 750315371 transformer for isolated power
• Measurement side: ESP32-S3R8 MCU with 16 MiB SPI flash, 2.4 GHz PCB antenna, 3.3 V rail (SY8089 buck)

Measurement Modes

Mode	Front-end
Voltmeter	3-stage resistive divider (10 MΩ → 2 MΩ → 523 kΩ), OPA388 buffer, TS5A3359 range switch
Ammeter	INA219 across 0.1 Ω shunt, GAQY212 photorelay for high-current gating
Resistance	TS5A3166 range switch, dedicated front-end
Capacitance	TS5A3166 range switch, dedicated front-end
Inductance	LMV331 comparator, resonant-discharge measurement

All five modes share a single ADC path through analog muxing, with only one active at a time¹.

Software

The card uses a browser-based app over Web Serial API (Chrome/Edge) — no drivers, installers, or accounts required¹. Features include:

• Big readout with mode selector (V AC / V DC / A AC / A DC / Resistance)
• Min/avg/max tracking
• Live chart with CSV export
• Serial console tab
• Wire protocol: plain text at 115200 baud (MODE:VDC, READ, LOG:START)

A mobile app over BLE (via the ESP32-S3) is planned¹.

Specifications

Specification	Details
MCU	ESP32-S3R81
USB isolator	ADuM4160BRWZ (5 kV)1
Isolation	Galvanic (data + power)1
Wireless	WiFi + BLE (ESP32-S3)1
Front-end	Chopper-stabilized OPA388, TS5A3359 mux1
Host software	Web Serial API (browser-based)1
License	Open source (CERN-OHL-S hardware, MIT firmware)3
Source	HW-Lab-Hardware-Design-Agency (GitHub)3

Related Projects

Project	Description
DockFrame	HW Media Lab's modular USB-C hub hosting this card
Power Supply Card	Programmable bench supply in the same Tool Card format
Breadboard Card	XIAO-based development card in the same Tool Card format

Footnotes

1. Building a Multimeter in a Framework Expansion Card — HW Lab Blog ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴

2. DockFrame — HW Media Lab LLC ↩

3. HW-Lab-Hardware-Design-Agency — GitHub ↩ ↩² ↩³ ↩⁴