A CARD IN A SPARE PCIE SLOT PRESSES YOUR PC POWER BUTTON FOR YOU, FROM ANYWHERE
A PCIe x1 card that presses your desktop's power button from Home Assistant, powered by the slot's standby rail so it works with the machine switched off.
by scavenrage
AutomationOpen-hardware
Built withESP32Raspberry Pi
- difficulty
- ●●●●○
- time
- a weekend
- license
- CERN-OHL-P-2.0
- repo
- repo ACTIVE88 stars
●●●●○ · a weekend · CERN-OHL-P-2.0 · 88 stars · repo ACTIVE
WHAT YOU’LL NEED
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COMPAREE VERDICT
This is an open hardware answer to remote PC power that does not involve a Raspberry Pi hanging off a USB port or a relay bodged onto the motherboard. It takes 3.3 volts from the PCIe slot's auxiliary rail (pin B10), which stays live in standby, so the card is awake when the PC is off and needs no extra cable. Two MOSFETs pulse the motherboard's power and reset headers for 300 milliseconds, exactly like a finger on the case button, and a sense pin on the switched 3.3 volt rail reports whether the machine is actually running, so Home Assistant knows the real state instead of guessing. The passthrough headers mean the physical buttons keep working. The catch is that this is an SMD build: the README gives a short 10-step assembly list, the BIOS settings you need (ErP off, Power on by PCI-E on) and a checklist to verify before the first flash, but no photo walkthrough — you still have to match PWR_SW and RESET to your motherboard's front panel header. If your board does not use a standard front panel connector, you are on your own. Gerbers, BOM and pre-built firmware binaries are all in the repo, and a standard HASL board works, with ENIG gold fingers recommended for durability. If you can solder an ESP32 module and SMD parts and have a use case that justifies a weekend, this is a neat, well-documented way to do it.
IN THE REPO
GOOD TO KNOW
- —Full schematic, PCB layout and bill of materials published on OSHWLab under CERN-OHL-P-2.0, EasyEDA source files included.
- —Zigbee firmware is in the repository, built for the ESP32-H2-MINI-1-N4 module.
- —Short 10-step assembly list, required BIOS settings and a pre-flash checklist are in the README; no photo-by-photo guide, so you match the front panel pins to your motherboard yourself.
- —Licence is CERN-OHL-P-2.0, a permissive open hardware licence: commercial use and closed modifications are allowed, as long as the licence notice and attribution are kept.
- —Two-layer, 1.6 mm board; ENIG recommended for durable gold fingers, HASL works fine electrically.
- —No case or enclosure files — the card sits bare in the slot.
Parts to buy
7 itemsFrom our check of the build. Exact quantities and part numbers are in the creator’s BOM.
Can I build this?
This build involves mains voltage — for adults comfortable with electrical work only.
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
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Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Review the schematic and BOM, then grab the ready Gerbers from hardware/Gerber_PCB.zip in the repo (Interactive schematic, PCB view and BOM — read both before ordering parts.)
- 2.Order the PCB (1.6 mm, ENIG or HASL) from any PCB fab using the Gerbers in hardware/Gerber_PCB.zip(Specify 1.6 mm thickness. ENIG gives more durable gold fingers, but the author says HASL works equally well electrically; if you choose ENIG, remove the solder mask over the finger area on both layers.)
- 3.Source the ESP32-H2-MINI-1-N4 module and passives from the BOM(Everything you need is listed in hardware/BOM.xlsx and on OSHWLab.)
- 4.Flash the Zigbee firmware through the U9 UART header after assembly (Use the pre-built files in binaries/ with esptool.py, or build with ESP-IDF; later updates can go over the air via Zigbee OTA.)
- 5.Identify the PWR_SW and RESET pins on your motherboard's front panel header(Consult your motherboard manual — not every board labels them the same way, and some use non-standard pinouts.)
- 6.Wire the card's output headers to the motherboard and the case buttons in parallel(The passthrough headers mean the physical buttons keep working; test them before you close the case.)
- 7.Pair the card with your Zigbee coordinator and add it to Home Assistant(Set ErP Ready to Disabled and Power on by PCI-E to Enabled in the BIOS first. It should then appear as a switch with power state feedback; if it does not, check the sense pin is reading the switched 3.3V rail.)
KNOWN ISSUES
- Not every motherboard breaks out PWR_SW and RESET to a standard header — some laptops and SFF builds wire the button directly to the board, and this card will not work.
- The README targets motherboards with a standard front panel connector (JFP1 or equivalent). If your case or board uses a proprietary connector, you will need to make an adapter.
- The firmware is built for the ESP32-H2-MINI-1-N4 module specifically — if you substitute a different ESP32 variant, you will need to recompile and possibly rewrite the Zigbee stack.
- Order at 1.6 mm thickness. ENIG gold fingers are recommended for durability, but a standard HASL board works electrically — if you choose ENIG, remove the solder mask over the finger area on both layers.
- The sense pin reads the slot's switched 3.3V rail to detect whether the PC is on. The firmware assumes HIGH means on — check the polarity with a multimeter before the first flash and flip one comparison in pc_sense.c if your board reads the other way.
- The assembly list is short — use the interactive OSHWLab schematic/PCB view to check component placement before you reflow.
Does this work with laptops?
No. Laptops do not expose a PCIe slot you can plug a card into, and they do not break out the power button to a header you can intercept.
Can I use this to wake a PC from sleep, or does it only work from full shutdown?
The README documents power-on from full shutdown (S5): the card is powered from the 3.3Vaux rail, which stays live in standby. It simulates a power-button press, so from sleep it behaves like your case button does on that board.
Why Zigbee instead of WiFi?
The ESP32-H2 deliberately has no WiFi radio — only Bluetooth LE and 802.15.4. That makes it a pure Zigbee device that cannot be reached from the internet unless you expose Home Assistant itself, which is a different security boundary.
What happens if the card loses power while the PC is running?
Nothing. The card only switches the power button header; it does not interrupt the PC's own power rails. If the standby rail fails, the card goes dark but the PC keeps running.
Can I reset the PC remotely, or is it power-only?
The card has a separate RESET output that pulses the motherboard's reset header for 300 ms. In Home Assistant it shows up as a switch that turns itself back off after the pulse.
Community builds
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Discussion1
FROM THE COMPAREE TEAM
The sense pin on the switched 3.3V rail is the detail that makes this more than a toy — it reports whether the PC is actually running instead of assuming the last command worked. Have you built a remote power project that guessed wrong?
scavenrage
scavenrage published this as an open hardware project under CERN-OHL-P-2.0 to get full remote power management of a desktop PC as part of a voice-controlled smart home, with no external relay module, no extra power cable and no visible hack. The design uses the PCIe slot's standby rail so it needs no extra cable, and the sense pin gives real power state feedback instead of guessing.
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- 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.
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CompareeTEAM2mo agoedited
Practical notes from our verification: the repository contains the Zigbee firmware, prebuilt binaries you can flash with esptool, Gerbers, a schematic and a BOM, with an interactive schematic, PCB view and BOM on OSHWLab. The README has a ten-step assembly sequence and a 'Before you build' checklist, and both are worth reading first. Two settings trip people up: in the BIOS you need ErP Ready disabled and Power on by PCI-E enabled, otherwise the card has no standby power to work with. For the PCB, order 1.6 mm thickness; the author recommends ENIG for durable gold fingers but says HASL works equally well electrically. Before the first flash, the README asks you to confirm the sense polarity with a multimeter — the firmware assumes high means the PC is on, and if your board reads the other way you flip one comparison in the code. The passthrough headers keep the case's own power and reset buttons working alongside the card. Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.