Electronics Module Boards Library

A collection of modular electronics boards (MOBs) and CAD resources for rapid prototyping and interfacing.

These MOdule Boards (MOBs) are useful for:

• doing experiences
• testing specific components functions
• prototyping complex projects by modular approach
• interfacing and expanding hardware sub-systems
• having fun building simple circuits

The MOBs Library

MOdule Boards Status Legend

• [Designed] Development: Schematic completed. Ready for PCB layout and physical assembly.
• [Prototyped] Built: Physical board assembled. Ready for bench testing and verification.
• [Validated] Ready: Hardware verified on the bench and circuit documentation completed.
• [Legacy] TEBO: Legacy board from the previous TEBO standard, non-compliant with the current MOB standard:
  • Power Supply Polarity: Often reversed (Positive on the Right on the PWR connector).
  • Missing Features: No onboard power status LED or dedicated bulk capacitor.
  • Connectors: Non-standard Molex-KK.

MOBs for PSU eXPeriences

Module	Description	Voltage Range	Status
mob-psu-5v	Linear 5V ($V_{CC}$) PSU	5.0V	[Validated]
mob-psu-cbank-26.4mF	26.4 mF Capacitor bank	3.3–5.0V	[Validated]
mob-psu-distribution	Eight-lines power bus expansion	3.3–9.0V	[Validated]
mob-psu-vdivider-pot-2x	Dual potentiometers voltage-divider	3.3–9.0V	[Validated]
mob-psu-vdivider-buf	Dual buffered voltage divider ($V_{CC}/2$ and $V_{CC}/4$ references)	3.3–9.0V	[Designed]
mob-psu-resistive-18R8	18.8 Ohm resistive load (266mA @ 5V, 479mA @ 9V)	3.3–9.0V	[Validated]

MOBs for Digital eXPeriences

Module	Description	Voltage Range	Status
mob-io-array-led-8x	Eight LED output array	3.3–5.0V (logic)	[Validated]
mob-io-array-switch-8x	Eight switch input array	3.3–5.0V (logic)	[Validated]
mob-io-array-switch-and-led-4x	Quad switch input array and quad LED output array	3.3–5.0V (logic)	[Validated]
mob-io-matrix-led-4x4	4x4 output led matrix	3.3–5.0V (logic)	[Designed]
mob-io-matrix-switch-4x4	4x4 input switch matrix	3.3–5.0V (logic)	[Validated]
mob-if-midi	MIDI IN/OUT/THRU interface	3.3–5.0V (logic)	[Validated]
mob-if-rs232	RS-232 interface	5.0V (logic)	[Designed]
mob-mcu-pic16f6x8	Microchip PIC16F6x8 microcontroller board	5.0V (logic)	[Validated]

MOBs for Audio eXPeriences

Module	Description	Voltage Range	Status
mob-audio-psu-9v-5v	Dual linear 9V ($V_{CC}$) and 5V ($V_{DD}$ or $V_{REF}$) PSU	5.0–9.0V	[Validated]
mob-audio-jack	Audio TRS jack 1/4" to pin-header adapter	—	[Validated]
mob-audio-io-stage	Audio input and output buffered stages	5.0–9.0V	[Prototyped]

Old MOBs (TEBO Legacy)

Module	Description	Voltage Range	Status
tebo-psu-5v	Linear 5V ($V_{CC}$) PSU	5.0V	[Legacy]
tebo-fn-clock-822	Programmable Clock 8 KHz to 22 KHz	5.0V (logic)	[Legacy]
tebo-if-midi-in	MIDI IN interface	5.0V (logic)	[Legacy]
tebo-if-midi-out	MIDI OUT interface	5.0V (logic)	[Legacy]

Specifications

Schematics and PCB layouts are designed with ExpressPCB free CAD software.

MOBs naming convention

• mob (module board base)
• mob-psu (power supply & power conditioning units)
• mob-io (input/output units)
• mob-if (communication & interface units)
• mob-fn (specialized function units)
• mob-mcu (microcontroller host units)
• mob-audio (audio signal units)

Baseline Hardware Rules

To maintain consistency and simplify assembly across all MOBs, the following baseline rules were adopted where possible:

• Paperboard Grid Sizes: $2\times8\text{cm}$, $4\times6\text{cm}$, $5\times7\text{cm}$, $7\times10\text{cm}$
• Power Connection: Standard power connector (PWR) with positive pin on the left, bulk capacitor ($C$), and power-on indicator LED (DL).
• Activity Indicator LEDs:
  • 3mm Green LED: Power status
  • 3/5mm Green LED: Normal activity
  • 3/5mm Yellow LED: Warning status
  • 3/5mm Red LED: Error / fault status
  • 3/5mm Blue LED: Manual intervention required
• LED Current Limiters ($1\text{k}\Omega$ @ 3V3 and 5V, $2.2\text{k}\Omega$ @ 9V): Calculated for standard 3mm/5mm LEDs to target $I_F \approx 1\text{mA} - 3\text{mA}$. This provides clear visual indication while minimizing total power consumption on the supply rails.
• Digital Line Pull-Ups ($10\text{k}\Omega$): Standard trade-off value offering noise immunity for low-frequency/static digital lines while keeping active-LOW state power waste below $0.5\text{mA}$ (@ 5V). For high-impedance CMOS logic inputs, the voltage drop across the resistor is negligible ($V_{IH} \approx V_{CC}$). For TTL inputs (where input leakage current $I_{IH}$ causes a small voltage drop $V_{drop} = I_{IH} \cdot R$), a single $10\text{k}\Omega$ pull-up maintains $V_{IH}$ well above the TTL logic HIGH threshold ($2.0\text{V}$).
• IC Decoupling ($100\text{nF}$ Ceramic): Placed as close as possible to IC power supply pins to suppress high-frequency switching transients and localized noise.
• Board Bulk Capacitance ($10\mu\text{F}$ Tantalum/Electrolytic): Acts as a local energy reservoir to smooth out low-frequency power supply ripple and step-load variations across board interconnects.

ExpressPCB Custom Component Library

Layouts and schematics are designed using ExpressPCB (free CAD software) and the custom library stored in expresspcb/:

• Custom components follow the format _MOB_<name>_<size>
• Board templates follow the format _MOB__Paperboard_<size>
• ExpressPCB size units are $1/10$ of an inch ($0.1"$)
• Standard trace width: $0.05"$ ($50\text{ mil}$), pad diameter: $0.065"$
  • Note: A $50\text{ mil}$ trace on 1 oz copper provides up to $\approx 900\text{mA}$ continuous current capability under worst-case thermal and loading constraints ($50^\circ\text{C}$ ambient, $J = 20,\text{A/mm}^2$ conservative density), while bounding ohmic drop below $20\text{mV}$ on standard board runs (ref. xp-hardware: Conductors & Wiring).

Changes

See file CHANGES for the project resources change log.

Future Plans for the MOBs Library

• Add more MOBs!

About & License

Author: Alessandro Fraschetti (gom9000).
Technical Notes: The hardware design was supported by ExpressPCB and the custom expresspcb-goslib libraries.
License: This project is licensed under the MIT License.