Atx psu controller

ATX Power Supply Controller (psu-controller)

A discrete, analog hardware controller designed to sequence and manage standard ATX power supplies for non-standard motherboards, repurposed compute platforms (such as the AMD BC-250 mining board), single-board computers, and custom electronics fixtures.

📖 Table of Contents

• Motivation & Problem Solved
• Key Features
• System Architecture
• Theory of Operation
• Header Pinout & Wiring
• Bill of Materials (BOM)
• PCB Layout & Manufacturing Specs
• Bench Testing & Verification
• Host BIOS Configuration
• Repository Structure
• Documentation Index
• License

⚡ Motivation & Problem Solved

Repurposed compute hardware (such as headless crypto-mining boards like the AMD BC-250, embedded industrial boards, and retro computing conversions) often lack standard front-panel ATX power management circuits.

Without a dedicated controller:

1. The Green Wire Hack: Operators typically short the ATX PS_ON# wire (green) to Ground (black) with a jumper clip or switch.
2. 24/7 Power Waste & Wear: The power supply and all chassis fans remain powered continuously at high wattage—even after the operating system cleanly halts and unmounts disks.
3. Loss of ACPI Control: Pressing a chassis button cannot trigger an ACPI graceful shutdown, risking filesystem corruption.

The ATX Power Supply Controller eliminates jumpers by providing an intelligent, fully autonomous, discrete hardware sequency bridge between any ATX power supply, the host motherboard, and your chassis buttons/LEDs.

✨ Key Features

• Cold Boot RC Sequencing: Momentary chassis button tap charges a timing capacitor ($C_{hold} = 22\ \mu\text{F}$ via $R_{bleed} = 120\text{ k}\Omega$), asserting ATX PS_ON# for ~3.5 seconds to allow the host to spin up.
• Active Telemetry Latching: Continuously monitors host power state via a 3.3V telemetry pin (e.g., TPM header pin HOST_ON). Once booted, host voltage locks PS_ON# low indefinitely.
• Safe ACPI Button Mirroring: Routes button pulses to the host's power button pad (BTN_OUT) through an open-drain N-channel MOSFET (2N7000), allowing:
  • Short tap (200 ms): Graceful OS ACPI shutdown without dropping ATX main power prematurely.
  • Long press (4.0 seconds): Hardware-level emergency forced power cut when OS kernel freezes.
• Automated Standby Transition: When the operating system finishes shutting down, HOST_ON drops to 0V. The controller de-asserts PS_ON# within 300 ms, putting the ATX power supply back into standby ($< 50\ \mu\text{A}$ quiescent draw).
• Remote Microcontroller Wake (ESP_WAKE): Accepts a 3.3V logic pulse from an ESP32, ESP8266, or Raspberry Pi Pico to power on the system remotely over WiFi/Bluetooth.
• Hardware Remote Inhibit: Uses an NPN transistor clamp to hardware-shunt ESP_WAKE directly to ground whenever the system is running, preventing accidental resets or wake loops.
• Chassis Power LED Driver: Built-in low-side switched driver (~15 mA) indicates true host system state.
• 100% Discrete Through-Hole Parts: Built entirely with cheap, universally available "jellybean" components (TO-92 transistors, axial 1/4W resistors, DO-41 diodes, radial capacitors).
• DIY Single-Sided PCB Design: 1-layer bottom copper routing (B.Cu only, zero vias, zero top-side copper traces) designed specifically for home etching (toner transfer / photoresist) or desktop CNC milling.

🏗 System Architecture

+---------------------+               +-----------------------+
|   Chassis Front     |               |    ATX Power Supply   |
|       Panel         |               |      (24-Pin Main)    |
|                     |               |                       |
| [Power Button]      |               |  Pin 9  (+5VSB, Purp) |
| [Power LED Ring]    |               |  Pin 16 (PS_ON#, Grn) |
|                     |               |  Pin 3  (GND, Blk)    |
+----------+----------+               +-----------+-----------+
           |                                      |
           | 4 wires                              | 3 wires
           v                                      v
     +-----+--------------------------------------+-----+
     |                                                  |
     |         ATX POWER SUPPLY CONTROLLER PCB          |
     |          (55 mm x 45 mm Single-Sided)            |
     |                                                  |
     +-----+--------------------------------------+-----+
           ^                                      ^
           | 2-3 wires                            | 2 wires
           |                                      |
+----------+----------+               +-----------+-----------+
| ESP32 / ESP8266     |               |   Host Motherboard    |
| Microcontroller     |               |     (AMD BC-250)      |
|                     |               |                       |

🔬 Theory of Operation

========================================================================================
                          CIRCUIT SCHEMATIC OVERVIEW
========================================================================================

                                  +5VSB (J1 Pin 1, ATX Pin 9)
                                       |
                +----------------------+-------------------------------+
                |                      |                               |
            [R1: 10k]             Source [Q1: BS250]               [R_led: 330R]
                |                    (P-Ch MOSFET)                     |
  BTN_IN -------+------------------+ Gate                              v Anode
  (J3 Pin 1)    |                      | Drain                      [Power LED]
             [C_deb: 100nF]        [D2: 1N5819]                     (J4 Pin 1)
                |                      |                               | Cathode
  GND ----------+                      v                               (J4 Pin 2)
                                 Node [V_GATE]                         |
  HOST_ON (3.3V TPM) -----[D1: 1N5819]-+                               |
  (J2 Pin 1)                           |                               |
                                       |                               |
  ESP_WAKE (3.3V) ----[R5: 1k]---------+-----[D3: 1N5819]--+          |
  (J5 Pin 2)          |                                    |          |
                   Collector                               v          |
                      |                             +-------------+   |
  HOST_ON ---[R6: 10k]+ Base [Q5: 2N3904]           | [C_hold]    |   |

1. Standby (Off): ATX mains is plugged in. +5VSB is active. Node V_GATE is 0V, $Q_2$ is OFF, PS_ON# floats at 5V, power draw is $< 50\ \mu\text{A}$.
2. Cold Power-On: Pressing the chassis button pulls $Q_1$ gate low, turning $Q_1$ ON. A 5V pulse charges $C_{hold}$ ($22\ \mu\text{F}$) through Schottky diode $D_2$ in $< 2\text{ ms}$, immediately turning ON $Q_2$ and pulling PS_ON# to GND.
3. Hold-Up Timer: Once released, $C_{hold}$ discharges through $R_{bleed}$ ($120\text{ k}\Omega$). $Q_2$ remains fully saturated for ~3.5 seconds, giving the host ample time to power on and initialize.
4. Active Latching: As the host boots, its 3.3V TPM header asserts HOST_ON. Diode $D_1$ conducts, locking V_GATE to ~3.05V indefinitely.
5. ACPI Button Mirroring: While running, pressing the front panel button turns on $Q_3$, pulling the motherboard power pad (BTN_OUT) to ground. The OS registers the ACPI event and initiates a clean shutdown. PS_ON# stays grounded by HOST_ON during shutdown.
6. Graceful Power Cut: When the OS halts, the motherboard turns off and HOST_ON drops to 0V. $D_1$ stops conducting, $C_{hold}$ discharges in ~300 ms, $Q_2$ turns off, and the ATX supply turns off main rails.
7. Emergency 4-Second Override: If the OS freezes, holding the button for 4.0 seconds holds BTN_OUT low, triggering the motherboard hardware supervisor force-off.
8. Remote Wake & Hardware Inhibit: A 3.3V pulse on ESP_WAKE charges $C_{hold}$ via $D_3$, turning on the PSU. When the host is already running, $Q_5$ clamps the wake input directly to GND, preventing unexpected glitches.

🔌 Header Pinout & Wiring

[!TIP] Use an ATX 24-pin extension cable to tap Pin 9 (+5VSB), Pin 16 (PS_ON#), and Ground without altering or cutting your power supply harness.

For full pinouts, motherboard solder points, and step-by-step assembly advice, see docs/wiring-guide.md.

📦 Bill of Materials (BOM)

All components are standard through-hole parts with wide global availability:

For detailed component substitutions, pinouts, and purchasing links, see docs/bom.md.

🛠 PCB Layout & Manufacturing Specs

The PCB is built in KiCad 8 as a true single-sided layout:

• Board Dimensions: $55.0\text{ mm} \times 45.0\text{ mm}$
• Layer Stackup: 1-Layer Copper (B.Cu bottom solder side only). Zero copper traces on F.Cu, zero vias.
• Top-Side Crossover Strategy: Resistor R2 ($10.16\text{ mm}$ axial span) and diode D1 ($7.62\text{ mm}$ axial span) act as natural component bridges across bottom copper traces on B.Cu, avoiding the need for wire jumpers.
• DIY Etch / Desktop CNC Milling Tolerances:
  • Power / Ground Traces: 0.80 mm
  • Signal Traces: 0.60 mm
  • Minimum Copper Clearance: $\ge 0.45\text{ mm}$
  • Component Pads: 1.80 mm outer diameter (0.8 mm drill)
  • Connector Pads: 2.00 mm outer diameter (1.0 mm drill)
  • Expanded TO-92 Footprints: $\ge 2.54\text{ mm}$ lead spread for easy hand soldering and generous isolation.

Manufacturing Files (kicad/gerbers/)

• atx-psu-controller-B_Cu.gbr — Bottom copper layer (traces & ground plane)
• atx-psu-controller-B_Mask.gbr — Solder mask (bottom)
• atx-psu-controller-F_SilkS.gbr — Top silkscreen (component placement & polarity)
• atx-psu-controller-Edge_Cuts.gbr — Board outline
• atx-psu-controller-PTH.drl — Excellon drill file (component holes only, no via drills)

🧪 Bench Testing & Verification

Before installing into your system, complete bench verification using a DC power supply and multimeter:

1. Pre-Power Continuity Check: Measure resistance between +5VSB and GND ($> 100\text{ k}\Omega$), and between PS_ON# and GND ($> 1\text{ M}\Omega$).
2. Standby Current Draw: Apply 5.0V to J1.1. Quiescent current must measure $< 50\ \mu\text{A}$ (typically $\sim 12\ \mu\text{A}$).
3. Cold Boot Hold-Up Time: Tap BTN_IN to GND. PS_ON# drops to $< 0.1\text{V}$ instantly and remains low for $2.5\text{s}$ to $3.5\text{s}$ before releasing.
4. Telemetry Latch: Apply 3.3V to HOST_ON within 2 seconds of button press. PS_ON# stays latched low indefinitely; the status LED lights up.
5. ACPI Button Mirroring: Tap BTN_IN. BTN_OUT pulses low ($< 0.1\text{V}$) while PS_ON# remains held low without interruption.
6. Graceful Shutdown: Remove 3.3V from HOST_ON. PS_ON# releases within 300 ms, and the LED turns off.
7. Remote Wake & Inhibit: 3.3V pulse on ESP_WAKE starts the PSU. When HOST_ON is 3.3V, ESP_WAKE is clamped to ground by $Q_5$.

For full testing protocols and verification logs, see docs/testing.md.

⚙ Host BIOS Configuration

To take full advantage of automated cold-boot sequencing:

1. Enter your motherboard BIOS setup during boot (DEL or F2).
2. Go to Advanced $\rightarrow$ ACPI Configuration / Power Management.
3. Set "Restore on AC Power Loss" (or "State After G3") to Power On (or Always On).
4. Save and exit (F10).

The host motherboard will now automatically boot the moment the ATX controller supplies +12V power!

📁 Repository Structure

psu-controller/
├── docs/
│   ├── schematic.md         # Full ASCII schematic, netlist & circuit theory
│   ├── bom.md               # Complete Bill of Materials, footprints & substitutions
│   ├── wiring-guide.md      # Pinout, cable harnesses & motherboard solder points
│   ├── testing.md           # Bench test protocol, checklist & measurements
│   └── circuit-ideas.md     # Reference comparison (555 timers, flip-flops, latches)
├── kicad/
│   ├── atx-psu-controller.kicad_pro   # KiCad 8 project file
│   ├── atx-psu-controller.kicad_sch   # KiCad schematic
│   ├── atx-psu-controller.kicad_pcb   # KiCad single-sided PCB layout
│   └── gerbers/                       # Gerber RS-274X & Excellon drill files
├── openspec/
│   ├── config.yaml          # OpenSpec workspace configuration
│   ├── specs/               # Active system specifications
│   │   ├── atx-power-control/spec.md
│   │   └── pcb-layout/spec.md
│   └── changes/archive/     # Archived design proposals and implementation tasks
└── README.md                # Project documentation and user guide

📚 Documentation Index

• Circuit Schematic & Netlist
• Bill of Materials & Component Substitutions
• Hardware Wiring & Integration Guide
• Bench Testing & Verification Protocol
• Circuit Topology Research & Comparison
• OpenSpec: ATX Power Control Spec
• OpenSpec: PCB Layout Spec

📄 License

This hardware project is open-source and released under the MIT License.