OtterCAT

An HamRadio USB CAT interface.

Features

• USB is isolated through transformer for power, and dedicated IC for signals
• Two UART serial ports
• Main uart serial port is available as a real RS232 too
• Stereo input (one channel isolated through transformer, other is not)
• Stereo output (one channel isolated through transformer, other is not)
• Input and outputs have attenuator pot
• Isolated and non-isolated PTT triggers, can choose between RTS and DTR signals

KiCAD Requirements

KiCAD 6.x minimum.

Needed libraries checked out in the parent folder where the OtterCAT is: - https://dev.otter.sh/dashie/KiCad_libraries - https://github.com/Jana-Marie/KiCAD-libs

Photo

Pinouts

• RS232: Standard RS-232 port
• UART 1:
  • 1: GND
  • 2: TX
  • 3: RX
• UART 2 (Internal):
  • 1: GND
  • 2: TX
  • 3: RX
• PTT:
  • PTT1, isolated: 1: +, 2: -
  • PTT2, non-isolated: 4: +, 5: GND
• Audio:
  • OUT Left (isolated with 1:1 transformer): 1: audio, 6: -
  • OUT Right (non-isolated): 2: audio, 7: GND
  • IN Left (isolated with 1:1 transformer): 3: audio, 8: -
  • IN Right (non-isolated): 4: audio, 9: GND

Any pin denoted "GND" are all the common GND of the interface, pins denoted "-" are isolated grounds, either after an Optocoupler, or 1:1 Transformer.

Internal jumpers: - JP1: To enable EEPROM, only if components are provisioned - JP2: Choice between RTS or DTR for PTT1 trigger - JP3: Choice between RTS or DTR for PTT2 trigger

EEprom

The USB Hub can has an EEPROM provisioned, it will allows to only show two usb ports downstream, or change VID/PID etc.

By default no EEPROM is provisioned.

Test points

USB Side: - TP1: GND USB - TP2: 5V USB

Isolated side: (Don't test an isolated TP with an USB side GND) - TP3: 5V - TP4: GND

Assembly

• Interactive BOM reflecting main branch: here

Requirements for assembly file generation:

• KiKit
• ibom

Generate Fabrication Files with:

kikit fab jlcpcb --no-drc --field LCSC --schematic OtterCAT.kicad_sch --assembly OtterCAT.kicad_pcb fab

You can then upload fab/gerbers.zip to the fab house of your choice.

Project has been made and tested with JLCPCB PCB service, with default choices, nothing special.

Generating an Interactive BOM from older release or current:

# if you are on a specific release you would have done:
# git checkout 1.1
# then:
kibot -b OtterCAT.kicad_pcb -c kibot.ibom.yaml --out-dir=ibom
# then open ibom/index.html in your browser

Changelog

1.0 - Initial rev

1.1

• Added rev text to PCB
• Fixed 5V transformer placement
• Length matched USB Lines
• Fixed FE1.1s schematic
• 3.3V regulator removed
• Inverted the Enhanced and Standard UART interfaces
• Fixed RS232 Rx/Tx
• Fixed Rx/Tx leds
• Reduced Pwr/Rx/Tx leds resistor

1.2

• Changed UART1 jack
• Switched UART2 to a jack
• Switch PTT connector to dual jacks
• Stencil is same as 1.1
• Inverse pots direction

Projects worth mentioning

• The Digirig, another OpenSource CAT interface.

License & contact

• CERN Open Hardware Licence Version 2 - Strongly Reciprocal
• PJ-3136-B.kicad_mod is CC0 1.0 from https://github.com/tzarc/reversible-kicad/blob/master/reversible-kicad-footprints/PJ-3136-B.kicad_mod
• ottercat @ otter DOT sh

Available files