The Junkpile

Next Revision

For revision following 2025-11-A

Goals

Support PCIe x4 for those using Thunderbolt/USB4 or a single-wide Oculink connection.

Support PCIe x8 for those using a double-wide Oculink connection.

Officially it will still only be PCIe 3.0, but I’ll follow the design constraints of PCIe 4.0 so it will also work with USB5. PCIe 5.0 may be possible but it’s not a goal, since 4-layer stackups are not supported there.

Work with the OEM Power supply, because finding compatible replacements can be tricky.

Power an 80mm fan. Won’t try and re-use the OEM fan because it has a nonstandard connector and, chances are, the bearings on all those fans are shot now anyway.

Provide an auxiliary power connector (+3v3,+ 5v, +12v) for powering additional fans, USB hubs, etc.

Add Addressable LEDs to the “Alien Head”.

Be completely reversible, and require not “breaking changes” (pun intended) to the AGA chassis.

Todo

Base Board

Required

Adjust Screw Holes

  • Move screw holes south (toward far end of PCIe connector) by 1mm.

Change edge to x8 connector

  • Change the edge connector from x4 to x8. This will increase the size of the 4-layer portion by about 30%, from 55mm to 80mm.
  • look at adding a notch between x4 and x8 parts. NOT going to add a notch for x1 unless I find a premade footprint for it.

Add power interface to bridge board

  • 1/2 of 1808 fuse footprint. This has made the board about 2 mm wider.
    • Revisit this, the cost savings of a narrower board may justify placing the fuses elsewhere and using some other kind of jumper material

Misc

  • notch/divot to clear PCIe x16 pins on southmost end
    • added ruler to note required carveout

Power bridge board

Add secondary bridge board for power supply. This will be a 2-layer board since it doesn’t deal with high-speed signals and for cost reasons.

This section will be about 130mm in length.

Required

  • Double-Check the screw spacing
  • Re-check thermistor circuit — put it in circuitlab
  • REMEMBER: must provide clearance for an x16 mating connector from the baseboard!
  • No pins on this side of the PCIe connector will be connected. Even though the grounds will be shared anyway, don’t ground any PCIe pins on this board. It’ll be easier to add the grounding than it would be to take it away if it was done with infill.
  • Get 12v/3v3 from the ATX connector to the PCIe slot
    • With separate fuses for these — not shared with SATA power connector
    • With fuses serving as the bridge Revisit this, the cost savings of a narrower board may justify placing the fuses elsewhere and using some other kind of jumper material
  • provide an auxiliary connector for 12v/5v/3v3 power
    • 2x6 Minifit Jr (Molex 39-30-1060)
      • Copy the pinout used by Corsair
    • Add really large warning for users to check the pinout first
  • Header to toggle PS_ON as appropriate
    • “remote trigger” header with 3 pins: 1) gnd 2) pull-down - pull this pin to gnd to trigger PS_ON, a straight-shot to PS_ON on ATX connector 3) pull-up - pull this pin high to trigger PS_ON, low-side switch for PS_ON using transistor/mosfet
  • Have LEDs indicating power supply states
    • 3v3, 5v, and 12v LEDs
    • 5vSB
    • PS_ON and PWR_OK?
      • could help diagnosing problems and LEDs are cheap
      • Will I need to buffer PS_ON so the LED draw doesn’t accidentally turn the PS on?
      • PWR_OK is active-high (ATX 2.2 Spec, 4.1.3.3), 5V TTL signal
  • Fan connector for for existing 80mm
    • 2.54mm, don’t worry about using the old connector

Optional

  • Separate fuses for auxiliary power connector, separate from fuses for PCIe slot 12v/3v3
  • MCU to provide “sleeping” LED signal.
    • Powered by +5vSB
      • Note: ATX 2.2 Spec, 4.1.3.2 spec says max current of this pin is 2A
    • When PS_ON/PWR_OK is not asserted, will give “sleeping” effect
    • When PS_ON/PWR_OK is asserted, but no incoming PWM from host is detected, will give “power on” effect
    • When PS_ON/PWR_OK is asserted, and incoming PWM from host is also detected, the PWM will be passed through to the LED
    • Provide TTL serial breakout pins for runtime config without needing re-flash
    • I have AtTiny412 and ATTINY824 MCUs on hand, both SOIC
    • I have 74LVC1G3157GW,125 (TSSOP-6) ICs on hand
  • PWM control for fan
    • use 555 timer + potentiometer
    • Option for 3-pin, using mosfet driver, or 4-pin, using fan PWM signal
      • jumper pad to switch, or just two separate connectors?
    • Speed control by potentiometer
    • Speed control thermistor + potentiometer for offset, see 555 PWM with Thermistor for more info on parts and arrangement. Could R7, resistor between pin 7(DIS) and 8 (VCC) be replaced by the thermistor?
    • Include both footprint for board-mounted 0805 thermistor, and SMD JST connector relocatable thermistor

LED Board

  • Test current board
  • Adjust board so it fits without filing
  • Could microcontroller go on THIS board to free up space?