IbScaleSeqRails

ibScale Sequential Feeder Rails

Enhanced feeder rails for the Opulo LumenPNP. Provides power-up sequencing and port protection. These are desgined to be a drop-in replacement for the stock rails.

Front side of the 2-up panel: the 13-port blade (top) and 12-port blade (bottom), joined by a V-Cut.

Back side, showing per-port slot numbers and the optional LED fault indicator

The Problem

A fully loaded LumenPNP can have 50 feeders connected to the 24V feeder bus, each with its own 100uF input capacitor. When the machine powers up, every feeder starts charging its input capacitors at the same time. This massive capacitive load can sag (brown-out) the 24V bus or trip the power supply's over-current protection, causing the machine to restart or fail to power on.

The stock feeder rails also have no power protection on the exposed 24V surface contacts that feeders plug into. A dropped screw, a loose SMD part, or a faulty feeder motherboard can pull down the entire 24V bus and take out every feeder and possibly the machine at once.

The Solution

Each rail sequentially enables its feeder ports roughly 75ms apart, so feeders power up one at a time instead of all at once. Every port is individually current-limited and short-circuit protected, so a fault on one feeder doesn't affect the others on the shared bus.

Sequencing

• Each rail is built around an NE555 timer clocking a pair of 74HC595 shift registers, which walk a single "enable" bit down the row of ports, turning on one port roughly every 75ms until the whole rail has enabled all its ports.
• Rails are daisy-chainable: when one rail finishes sequencing, it hands off to the next rail in the chain, so an arbitrarily long run of rails (and therefore any number of feeder slots) sequences start-to-finish with a single trigger.
• A "FIRST" solder jumper lets a rail auto-start its own sequence at power-up instead of waiting for a hand-off signal. Only the first rail in a chain should have this jumper closed; every other rail waits for the previous rail to finish.
• A "LAST" solder jumper terminates the RS-485 network on that rail. Bridge all of its connections together on whichever rail is the last one in the daisy chain.

5-pin daisy-chain connector

The stock LumenPNP feeder rail connector is a 4-pin JST-PH (24V, GND, RS-485 A/B). To pass the sequencing hand-off signal from rail to rail, the IN/OUT connectors on this board use a 5-pin JST-PH instead — the extra pin carries the sequencing trigger alongside the pass-through power and RS-485 comms.

Because the LumenPNP wiring harness only uses a 4-pin housing you'll have to:

1. De-pin the terminals from the stock 4-pin housing.
2. Re-seat the terminals into a 5-pin housing, leaving the 5th (trigger) position empty.
3. Use the "FIRST" solder jumper on that rail to auto-start its sequence at power-up since there's no incoming trigger signal to wait for.

You will also need new 5-pin JST-PH cables to connect the rails together. These are relatively easy to order pre-made and inexpensive.

Port protection

Every feeder slot is switched through a TI TPS1H000A smart high-side switch, giving each port independent:

• Overcurrent limiting (24V @ 1A)
• Short-circuit protection
• Thermal shutdown
• Reverse polarity protection
• Backfeed protection
• Auto-restart
• Optional front side 0805 LED fault indicator

A fault at one feeder's surface contacts (loose debris, a shorted or bad feeder motherboard, etc.) trips only that port, instead of browning out or shutting down the entire 24V bus. During a detectable fault condition the port's optional fault indicator LED will turn on.

Board layout

This is a KiCad 10 project. The design is panelized as a 2-up panel with a V-Cut (the User.1 layer) down the middle:

• blade-12.kicad_sch — a self-contained 12-port sequencer rail (its own 555, shift registers, IN/OUT connectors, and FIRST/LAST jumpers).
• blade-13.kicad_sch — a self-contained 13-port sequencer rail, identical in function.

The panel is v-scored during production and simply needs to be snapped along the V-Cut line. This gives you a complete rail set for one side of the machine.

The project also defines a BackRails variant. This variant renumbers/relabels the silkscreen slot numbers for rails to be mounted on the rear of the machine, so front and rear rail slot numbering stays consistent without needing a permanent marker.

Each feeder slot also carries a DS28E07 1-Wire EEPROM, one per port, for slot/feeder identification. A second footprint for an AT21CS01 EEPROM has also been added for future feeder firmware updates that might support alternative EEPROM types.

RS485 network termination is improved with two 60-ohm resistors in series with a 100nf cap from the center to ground. This provides increased common-mode rejection and improved signal integrity.

There is an unpopulated LED on the back side of the board for an optional fault indicator. Any standard 0805 5V tolerant LED will work. There is a 810-ohm current limiting resistor already installed in series with the LED.

Repository layout

ibScaleSeqRails.kicad_pro     Project file
ibScaleSeqRails.kicad_sch     Top-level schematic (instantiates both blades)
ibScaleSeqRails.kicad_pcb     PCB layout (2-up panel, V-Cut on User.1)
blade-12.kicad_sch            12-port rail sub-schematic
blade-13.kicad_sch            13-port rail sub-schematic
library/                      Local symbols, footprints, and 3D models

Manufacturing

Bill of materials

• Every part has a manufacturer part number plus vendor-specific part numbers for DigiKey, Mouser, and LCSC.
• Standard 0603 footprints
• Caps X5R 50V
• Resistors 1%

PCB specification

• 4-layer stackup
• 7628 prepreg
• ENIG finish
• Capped or tented vias
• 0.3mm minimum drill size

Mounting holes

• Mounting holes need to be chamfered to locate the PCB into the LumenPNP rails.
• Chamfer depth: cut until the chamfer reaches the silkscreen circle around each mounting hole.
• Tooling: a 45° (preferred) or 60°, 1/4" (6mm), 4-6 flute carbide chamfer bit is needed. Standard FR4 PCB material will quickly dull a tool steel chamfer.
• Method: PCB material is thin, and it's easy to end up drilling through the board while attempting to hand-chamfer the holes. An easier method is to use a drill press with a quill or depth stop and an empty feeder body. The empty feeder body holds the board flat in the drill press. Set the drill press's depth stop so the chamfer comes out correct on the first hole, then repeat for the remaining holes/boards in a repeatable, efficient manner. This process creates fine fiberglass dust, so dust collection equipment is recommended.

License

Released under CERN-OHL-S-2.0. See LICENSE.txt for full terms.

Compatibility

Designed for the Opulo LumenPNP feeder rail system. Not affiliated with or endorsed by Opulo.