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YOU CAN BUILD THE MEASURING CARD CERN IS PUTTING INTO THE LHC

CERN published the schematics for the measuring card going into over a hundred LHC upgrade installations—a single-channel 32-bit ADC with optical isolation and 23 effective bits below 10 Hz.

by Nikolai Beev, CERN TE-EPC

FULL CAD BOM FIRMWARE DOCS

Open-hardwareScience

difficulty
●●●●●
time
several weekends
license
CERN-OHL-W-2.0
repo
repo ACTIVE0 stars

WHAT YOU’LL NEED

  • 3D printer + filament — printable parts — files are in the repo
  • Electronic parts — full list with part numbers in the repo BOM
  • Dev board / microcontroller — runs the project firmware

Partner

Show off your build — Record and edit your build video by editing the transcript, not the timeline.Try Descript
Videos
1

COMPAREE VERDICT

The OPT-ADC-10k-32b-1cha (HPM7177) is a single-channel 10 kSPS 32-bit ADC card built around the Analog Devices AD7177-2, published by Nikolai Beev at CERN for the High-Luminosity LHC upgrade. It measures very small, very slow-changing voltages with over 23 effective bits of resolution below 10 Hz, and the entire read-out and synchronisation path is optical fibre—no copper signal path in or out. Everything needed to replicate it is on CERN's Open Hardware Repository: schematics, PCB, gateware. Marco Reps built one from those files, including the reflow work and the 19-inch enclosure. This is a serious build. You will need reflow capability (or access to a board house that offers assembly), an FPGA toolchain, and the patience to work without a step-by-step assembly guide. The BOM is complete but you are sourcing it yourself. There is no firmware binary—you compile the Verilog and load it. The documentation tells you what the card does and how it is structured, but not how to bring it up or calibrate it. If something does not work, you are debugging it with a scope and the schematics. It is also expensive. The AD7177-2 alone is over 20 dollars in single quantity, the Vishay foil resistors add up quickly, and the SFP transceiver, FPGA module and precision references will push the total BOM past 300 dollars before the PCB or enclosure. For context, a used Keysight 3458A—the bench multimeter people reach for at this accuracy—goes for 5,500 to 9,000 dollars, so this is still far cheaper if you need precision and optical isolation, but it is not a budget project. The single most likely thing to go wrong is misunderstanding the scope. CERN describes resolution in effective bits, not digits (which is how bench meters are sold), and the performance claim is for bandwidths below 10 Hz. If you need a general-purpose high-accuracy voltmeter, this is not it. If you need a low-noise, optically isolated ADC for a specific measurement task and you can handle the bring-up, the design is sound and it is out there.

NOT IN THE REPO

  • —Schematics, PCB layout, gateware and an assembly drawing are all published under CERN OHL v2 weakly reciprocal (commercial use is allowed as long as changes are shared under the same licence).
  • —The BOM is complete and names specific part numbers (AD7177-2, Vishay foil resistors, SFP optical transceiver), but there is no procurement guide or suggested distributors.
  • —Documentation is sparse: a two-page PDF with the block diagram, specs and repository structure. No assembly manual, no calibration procedure, no bring-up checklist.
  • —The gateware is Verilog for the onboard FPGA. You will need Xilinx Vivado (the free WebPACK licence is enough for the Artix-7 used here, but it is a 20+ GB install).
  • —Version 2 is what is published and what Marco built. Prototype files from 2019 are still visible in the repo—do not work from those.
  • —This is not a turnkey kit. It is a working CERN design released so other labs can build it.

Can I build this?

Printnothing required (PCB fabrication and optional 19-inch enclosure)
BuyAD7177-2 ADC, Xilinx Artix-7 FPGA module, SFP optical transceiver, Vishay foil resistors, precision voltage references, passive components, PCB fabrication, optional 19-inch rack enclosure and hardware
Toolsreflow capability or board assembly service, soldering iron for through-hole parts, FPGA toolchain (Xilinx Vivado), oscilloscope for bring-up and debug, fibre-optic test equipment or a working SFP host for communication
SkillsSMD assembly or access to assembly service, FPGA gateware compilation and loading, circuit debugging, analog measurement principles, familiarity with precision ADC specs and effective-bit calculations
Timeseveral weekends: PCB ordering and assembly is a week or more off-clock, gateware build and first light is an evening, bring-up and troubleshooting without a guide could be several more evenings depending on what breaks
Cost$$$, dominated by the ADC, precision resistors, FPGA module and SFP transceiver—BOM is over 300 dollars before the PCB, and a 19-inch enclosure adds another cost layer
SafetyNone beyond ordinary electronics care. This is low-voltage instrumentation with optical isolation; there is no mains voltage, no lithium, no lasers beyond the SFP (which is eye-safe class 1 in normal use).

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

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Videos

Marco Reps build video

Marco walks through the published files and builds one, including reflow and final assembly into the rack enclosure. After roughly the 19-minute mark the video includes a clip from Keysight University (another channel), so treat any statements in that section as demonstration rather than claims about this specific card.

Gallery

Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Read the two-page documentation PDF on the OHWR project page (Block diagram, specs and repository structure. This is the only written guide.)
  2. 2.Download the V2 schematics, PCB and gateware from the repository (Do not use the 2019 prototype files—V2 is the published and verified version.)
  3. 3.Watch Marco Reps assemble one (Shows the physical build from reflow to enclosure. Treat the Keysight clip after 19 minutes as separate context, not a claim about this design.)
  4. 4.Extract the BOM and start sourcing parts(Part numbers are in the schematics. No distributor recommendations are provided.)

Resources

Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.

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KNOWN ISSUES

  • The repository contains prototype files from 2019. V2 is the current design—make sure you are working from the right revision before ordering anything.
  • There is no assembly manual or bring-up checklist. You are working from the schematics and block diagram, so budget time for figuring out the correct sequence and troubleshooting without a guide.
  • The gateware is Verilog source, not a compiled binary. You need Xilinx Vivado installed (free WebPACK edition works, but it is a large download and the toolchain has a learning curve if you have not used it before).
  • CERN specifies resolution in effective bits, not digits. A claim of '23 effective bits below 10 Hz' is not the same as an 8.5-digit meter spec, and the performance is bandwidth-dependent—do not treat this as a direct replacement for a bench multimeter.
  • The BOM will cost over 300 dollars before the PCB and enclosure. The precision parts (AD7177-2, Vishay resistors, voltage references) are not cheap in single quantity.
  • Without a calibration procedure in the documentation, you will need to validate the card's performance yourself if absolute accuracy matters for your application.

Is this actually in use at CERN?

Yes. It was designed by Nikolai Beev in CERN's TE-EPC group for the High-Luminosity LHC upgrade, and over a hundred units are planned for deployment.

Can I use this as a bench multimeter?

Not directly. It is a single-channel ADC optimised for low 1/f noise and stability below 10 Hz with optical readout, not a general-purpose meter. The interface is fibre and FPGA, not a front panel with a display.

What is the difference between effective bits and digits?

Effective bits describe noise-limited resolution at a given bandwidth (CERN claims over 23 effective bits below 10 Hz). Digits are a marketing term for bench meters (e.g. 8.5 digits on a Keysight 3458A). They are not directly comparable—bandwidth, integration time and measurement conditions all matter.

Do I need to build the 19-inch enclosure?

No, the card can work standalone if you can provide power and connect the fibre. The rack enclosure is for integration into standard lab or accelerator infrastructure.

Where do I get the PCB made?

Any board house that handles 4-layer PCBs. The Gerbers are in the repository. If you do not have reflow capability, look for a service that offers assembly (you will need to supply the BOM).

Community builds

No community builds yet — be the first, we feature the best ones.

Discussion1

FROM THE COMPAREE TEAM

Over a hundred of these are going into the High-Luminosity LHC upgrade, and the whole design is out there under CERN OHL. If you had access to 23 effective bits below 10 Hz with optical isolation, what would you measure?

CompareeTEAM1h agoedited

Practical notes from our verification: the OHWR project page has the schematics, PCB, gateware and a two-page overview PDF, but no assembly manual or bring-up guide—you are working from the block diagram and Marco's video. The gateware is Verilog source (Xilinx Artix-7, free Vivado WebPACK works), not a binary, so you need the toolchain installed. The BOM is complete with part numbers but no distributor links; expect over 300 dollars before the PCB. The biggest gotcha is the effective-bits claim: CERN never gives a digit count, and the 23-bit figure is for bandwidths below 10 Hz—do not treat this as a drop-in for a bench meter without understanding what you are actually getting. If you need optical isolation and low 1/f noise for a specific task and you can handle the bring-up, the design is sound. If you want a multimeter, buy a multimeter.

Nikolai Beev, CERN TE-EPC

Nikolai Beev designed the HPM7177 at CERN's TE-EPC group (Electrical Power Converters section) for the High-Luminosity LHC upgrade, where precise, optically isolated voltage measurement is required for over a hundred installations. Rather than procure a commercial solution, the design was built in-house and published under the CERN Open Hardware Licence so other labs and projects can replicate it.

Web

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  • Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
  • Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
  • Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
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