2 layers100 × 100 mm
2 layers125 × 104 mm
Hecuba
jflitton/hecubaRead-only imager for Priam DISKOS 8-inch Winchester drives: interface board, Pico 2 W firmware, and host recovery tools
- Size
- 125 × 104 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 48
- Nets
- 88
- Pads
- 299
- Tracks, vias
- 412, 58
- Pours
- 1
- Routed
- Yes
- KiCad
- KiCad 10.0 (file 20260206)
- Created
- 4 Sep 2026
- Updated
- 12 Sep 2026
Overview
Hecuba is an open-source printed circuit board by jflitton, from the jflitton/hecuba repository on GitHub, published under the MIT licence. It is a 2-layer board of 125 × 104 mm with 48 parts on 88 nets, routed with 412 tracks and 58 vias.
It is built around the SN74LVC4245ADWRE4, SN74LVC14ADRG3 and SN74LVC1T45DBVRE4. Its parts include 26 resistors, 10 capacitors, 5 ICs and 1 connector. It belongs with the interfaces and adapters boards and the RP2350 boards of this library.
Main components
3
SN74LVC4245ADWRE4
SOIC-24-300mil-40℃~+85℃ 1 2.7V~3.6V 24mA 24mA 4.5V~5.5V 8 Bidirectional Level translator Output enable high-impedance Tri-State SOIC-24-300mil Translators, Level Shifters ROHSTexas InstrumentsTranslators / Level Shifters
SN74LVC14ADRG3
SOIC-14-40℃~+125℃ 1.3V~2V 1.65V~3.6V 150mV~800mV 1uA 24mA 24mA 6 6.2ns@3.3V,50pF 74LVC Noise suppression function Push-pull Schmitt trigger SOIC-14 Inverters ROHSTexas InstrumentsInverters
SN74LVC1T45DBVRE4
SOT-23-6-40℃~+85℃ 1 1.65V~5.5V 1.65V~5.5V Bidirectional Level translator Power-off protection、Output enable high-impedance Push-Pull、Tri-State SOT-23-6 Translators, Level Shifters ROHSTexas InstrumentsTranslators, Level Shifters
README
hardware/README.mdHecuba hardware
KiCad project for the Hecuba interface board. It sits between a Priam DISKOS
8-inch Winchester drive's native 50-pin interface and a Raspberry Pi Pico 2 W
(ref A1), which runs the firmware in ../firmware. Rev 0.9A is fabricated,
assembled, and has imaged a full Priam 3450. Read-only by design.
Why a custom board
The Priam 3450 (about 35 MB, 3,600 RPM, 5 heads, 525 cylinders) fits none of the usual readers.
- No STEP line. Heads are positioned by a closed-loop voice-coil servo under an on-board 8035. A seek is a register write plus a Seek command, and the drive must be powered, spun up, and taking commands before it returns a bit.
- Not a flux interface. The drive does its own data separation and outputs recovered NRZ data plus clock on RS-422 pairs at 6.4 Mbit/s.
- The sector format belongs to the controller that wrote the disk (an Intel
iSBC 215 here), not to the drive. Decoding happens offline in
../software. - Not SASI, despite the 50-pin ribbon and 8-bit active-low bus. PRIAM has no REQ/ACK handshake and carries read data on separate differential pairs.
Building one
| Board | 2 layers, 125 x 104 mm, 1.6 mm. Signals on top; bottom is a ground pour with +5 V and +3.3 V routed through it as 1 mm paths |
| Tracks and vias | 0.2 mm signal, 1.0 mm power. Vias 0.6 mm / 0.3 mm hole (1.0 / 0.6 on power) |
| Smallest features | 0.2 mm track, 0.3 mm hole, 0.5 mm copper to edge |
| Packages | SOIC and SOT-23-6 ICs, 0805 passives. Hand-solderable in about an hour |
| Mounting | Four 3 mm plated holes, grounded |
| Parts list | bom/bom.csv, with a column for parts deliberately left unpopulated |
| Placement guide | bom/ibom.html, interactive; click a part to see where it goes |
All ICs are current-production TI parts as of 2026. Gerbers are plotted from KiCad when needed and are not committed.
Routing rules for a respin:
- Only READ DATA and READ/REF CLOCK need care. Route each as a tight parallel pair over unbroken ground, and keep the two pairs apart. No impedance control and no length matching (the skew budget at 6.4 Mbit/s is about 170 mm).
- Everything else is slow. Keep the 8 data-bus lines grouped.
- Damping resistors at the source, termination at the receiver, and each 100 nF capacitor hard against its power pin with its own ground via.
Parts
| Ref | Part | Function | Datasheet |
|---|---|---|---|
| A1 | Pico 2 W (RP2350) | Controller. Powers the board over USB | raspberrypi.com |
| U1 | SN74LVC4245A | 8-bit data bus, bidirectional. Direction set by the Pico (GP8) | ti.com |
| U2 | SN74LVC4245A | Outbound control lines: address, strobes, head select, read gate. Direction strapped | ti.com |
| U3 | SN74LVC14A | Schmitt-trigger inverters on INDEX, READY, SECTOR MARK | ti.com |
| U4 | AM26LV32E | RS-422 receivers for READ DATA and READ/REF CLOCK. Receive only | ti.com |
| U5 | SN74LVC1T45 | -RESET driver. Direction strapped | ti.com |
| J1 | 2x25 IDC header | 50-pin ribbon to the drive |
Termination
Measured on one drive. Measure yours before populating. The manual's generic values assume the controller terminates everything; this drive terminates most of the bus internally. Values were measured at the connector with the drive unpowered and the ribbon off.
| Part | Value | Fitted | Reason |
|---|---|---|---|
| R1-R16, R28 | 0 ohm | yes | Series damping on outbound lines. The drive terminates this bus at about 179 ohm; even 33 ohm in series lifts a logic low to about 0.72 V against a 0.8 V threshold. Fit 10 ohm or less only if a scope shows overshoot |
| R17 / R20 | 220 / 330 ohm | yes | INDEX pull-up and pull-down. INDEX measured open at the drive. Settles near 3.0 V released |
| R18-R19 / R21-R22 | 220 / 330 ohm | no | READY and SECTOR MARK are pulled up inside the drive (130 / 175 ohm measured). Fit only if J1 pin 28 is left unpowered |
| R26 | 1 k | yes | Bias across the CLOCK pair, which measured 95 ohm. 100 ohm here would load the pair to 49 ohm |
| R27 | 100 ohm | yes | Termination across the DATA pair, which measured 252 ohm |
| R29 | 10 k | yes | Pull-up on GP17 (-RESET). Holds reset deasserted through boot |
| C1-C8 | 100 nF | yes | Decoupling, one per power pin |
| C9 / C10 | 10 uF | yes | Bulk on each rail at the Pico's power pins |
| JP1 | 2-pin header | shunt open | +5 V to J1 pin 28 (terminator power). Not needed on the drive tested |
50-pin connector (J1)
| Signal | Pin | Direction | Connects to |
|---|---|---|---|
| DBUS 0-7 | 2-9 | both | U1 via R1-R8 |
| -READ GATE | 11 | to drive | U2 via R9 |
| -RESET | 13 | to drive | U5 via R28 |
| -WRITE GATE | 15 | to drive | not connected |
| -RD / -WR | 17 / 18 | to drive | U2 via R10 / R11 |
| +AD 1 / +AD 0 | 19 / 20 | to drive | U2 via R12 / R13 |
| -DRIVE SELECT 1 | 22 | to drive | ground (always selected) |
| -DRIVE SELECT 2-4 | 23-25 | to drive | not connected |
| +5 V to terminator | 28 | power | JP1 (open) |
| -HEAD SELECT 4 / 2 / 1 | 29 / 30 / 31 | to drive | U2 via R14 / R15 / R16 |
| -INDEX | 33 | from drive | U3, with R17 / R20 |
| -READY | 35 | from drive | U3 |
| -SECTOR MARK | 37 | from drive | U3 |
| WRITE DATA pair | 39 / 40 | to drive | not connected |
| WRITE CLOCK pair | 42 / 43 | to drive | not connected |
| READ/REF CLOCK pair | 45 / 46 | from drive | U4, R26 across |
| READ DATA pair | 48 / 49 | from drive | U4, R27 across |
Ground pins 1, 10, 12, 14, 16, 21, 26, 27, 32, 34, 36, 38, 41, 44, 47, 50 connect to the ground plane.
Power
- Drive rails (+24 V, +5 V, -5 V, -12 V, about 100 W total) come from a bench supply into the drive's own connector. The board neither carries nor senses them. Current-limit and watch +24 V at power-up; it runs the spindle and the voice coil.
- Board rails come from the Pico's USB. VBUS (pin 40) feeds the drive-facing side of the translators and the status pull-ups. The Pico's 3.3 V regulator (pin 36) feeds the Pico-facing side.
- Board draw is about 250 mA idle and 400 to 600 mA peak (the radio spikes on transmit). Use a 1.5 A supply or powered hub.
Power the Pico first, then the drive, and do not replug USB while the drive is powered. Until firmware init runs, the Pico's pins are inputs with pull-downs, which asserts every active-low control line through U2. Only -RESET is protected in hardware (R29).
Noteworthy facts
- Write lines have no copper. WRITE GATE, WRITE DATA, and WRITE CLOCK appear on the connector symbol only. No trace, no resistor. Writing would require adding wires to the board. The drive's own Write Enable switch is also off, and its internal terminator holds WRITE GATE deasserted.
- The drive is 5 V TTL; the RP2350 is 3.3 V and not 5 V tolerant. Every
signal crosses a translator. Net names carry the level:
DBUS0on the drive side,DBUS0_3V3on the Pico side. - Status lines invert. U3 inverts, so INDEX, READY, and SECTOR MARK read
active-high at the Pico while every other PRIAM signal is active-low. The
schematic writes active-low nets as
~{NAME}; the drive manual uses a leading minus. The full per-line chain is in../firmware/include/board_pins.h. - U3 is a Schmitt trigger on purpose. The drive's status outputs are open-collector 75462s with slow RC rising edges. Hysteresis turns each into one clean transition. The drive's own end uses 74LS14s for the same reason.
- U4 is the E variant on purpose. AM26LV32E adds hysteresis and an open-input fail-safe, so the read pairs hold a defined level before READ GATE asserts and before the drive's clock recovery locks.
- R29 is load-bearing. U5 has no output enable and follows GP17 from power-on, and the RP2350 boots GP17 as an input with a pull-down. Without R29 every power-up would reset the drive.
- DRIVE SELECT 1 is tied to ground. One drive, permanently selected, no chip-select GPIO. The data bus still only drives back during a read strobe.
- Unused U3 and U4 inputs are tied off. Floating Schmitt or differential inputs oscillate.
- R26 and R27 differ by 10x for two pairs on the same connector. Only measurement finds that.
Files
| Path | Contents |
|---|---|
hecuba.kicad_pro | Project settings, net classes, design rules |
hecuba.kicad_sch | Schematic, one sheet |
hecuba.kicad_pcb | Board layout |
hecuba.kicad_prl | KiCad UI state |
hecuba.kicad_sym | Five project symbols. PRIAM_50 is the drive connector with real PRIAM signal names |
footprints.pretty/ | Footprints for the four ICs, registered by fp-lib-table so the project opens standalone |
fp-lib-table | Points KiCad at the folder above |
lib/<PART>/ | Vendor symbol and footprint downloads per chip, untouched. Datasheets are linked from the parts table, not stored here |
bom/bom.csv | Parts list with populate / do-not-populate column |
bom/ibom.html | Interactive BOM |
.gitignore covers KiCad backups and netlist output.
License
CERN Open Hardware Licence Version 2, Permissive (CERN-OHL-P-2.0). The full text is in LICENSE. Keep the copyright and license notices with any copy or derivative of the design files, and on boards where practicable (the silkscreen already carries the author line). The design is provided as is, with no warranty, and the risk of building and using a board from it is yours.
Files under lib/<PART>/ are Texas Instruments vendor downloads under TI's own
terms and are not covered by this license.
Parts
48| Qty | Value | Footprint | References |
|---|---|---|---|
| 17 | 0Ω | Resistor_SMD:R_0805_2012Metric_Pad1.20x1.40mm_HandSolder | R1, R2, R3, R4, R5, R6, R7, R8, R10, R11, R12, R13, R14, R15, R16, R28 +1 |
| 8 | 100nF | Capacitor_SMD:C_0805_2012Metric_Pad1.18x1.45mm_HandSolder | C1, C2, C3, C4, C5, C6, C7, C8 |
| 4 | MountingHole_Pad | MountingHole:MountingHole_3mm_Pad | H1, H2, H3, H4 |
| 3 | 220Ω | Resistor_SMD:R_0805_2012Metric_Pad1.20x1.40mm_HandSolder | R17, R18, R19 |
| 3 | 330Ω | Resistor_SMD:R_0805_2012Metric_Pad1.20x1.40mm_HandSolder | R20, R21, R22 |
| 2 | 10uF | Capacitor_SMD:C_0805_2012Metric_Pad1.18x1.45mm_HandSolder | C9, C10 |
| 2 | SN74LVC4245ADWR | footprints:DW24-M | U1, U2 |
| 1 | 100Ω | Resistor_SMD:R_0805_2012Metric_Pad1.20x1.40mm_HandSolder | R27 |
| 1 | 10k | Resistor_SMD:R_0805_2012Metric_Pad1.20x1.40mm_HandSolder | R29 |
| 1 | 1k | Resistor_SMD:R_0805_2012Metric_Pad1.20x1.40mm_HandSolder | R26 |
| 1 | AM26LV32EIDR | footprints:D16-M | U4 |
| 1 | POWER TERMINATION | Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical | JP1 |
| 1 | PRIAM_50 | Connector_IDC:IDC-Header_2x25_P2.54mm_Vertical | J1 |
| 1 | RaspberryPi_Pico_2W - RP2350 | Module:RaspberryPi_Pico_W_SMD_HandSolder | A1 |
| 1 | SN74LVC14ADR | footprints:D14-M | U3 |
| 1 | SN74LVC1T45DBVR | footprints:DBV0006A_M | U5 |
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Questions
How big is the Hecuba PCB?
It measures 125 × 104 mm and has 2 copper layers, 1.6 mm thick.
What parts does the Hecuba use?
48 parts, built around the SN74LVC4245ADWRE4, SN74LVC14ADRG3 and SN74LVC1T45DBVRE4. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the Hecuba KiCad files?
From the jflitton/hecuba repository on GitHub, at the commit this page was made from: the board is hardware/hecuba.kicad_pcb and its schematic hardware/hecuba.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the Hecuba design in my own project?
Its repository publishes it under the MIT licence: you may reuse it on that licence's terms (keep the author's notice, and for a copyleft licence share your changes alike).