Create a complete new schematic and PCB-ready design for a single-channel Universal I/O controller based on an ATmega328 microcontroller.
Core requirement:
Design a new circuit from scratch. Do not reuse or include LM76202QPWPRQ1, AD7708, HC595, CD4066, LM2902, or other external switching/ADC/control ICs unless absolutely required and explicitly approved. The ATmega328 should directly measure and control the universal I/O as much as practical.
Universal Input requirements:
The same field input connector must support software-configurable modes:
- Digital input
- Analog voltage input
- 0–10 V input
- 0–20 mA input
- Resistance measurement
- RTD measurement: PT1000 and NI1000
- Thermistor measurement: 10k Type II and 10k Type III
Universal Output requirements:
Provide a software-configurable universal output from the ATmega328. Include at minimum:
- Digital output
- PWM-based analog voltage output using filtering/buffering if needed
- Clearly document whether true 0–10 V output or 0–20 mA output is supported directly, requires extra circuitry, or is out of scope for the first revision.
Architecture constraints:
- Use ATmega328 ADC pins directly for measurements.
- Avoid HC595 shift registers.
- Avoid CD4066 analog switches.
- Avoid LM76202 protection IC.
- Avoid AD7708 external ADC.
- Prefer simple discrete protection, resistor dividers, shunt resistors, RC filters, jumpers or low-cost analog selection methods if needed.
- Use clear ALL_CAPS net names.
- Design for a 24 V industrial field environment where possible, but keep MCU pins protected within safe voltage/current limits.
Expected schematic blocks:
- Power input and regulation for ATmega328 logic rail.
- ATmega328 core: power pins, reset, clock option, ISP/programming header, decoupling.
- Universal input field connector with protection.
- 0–10 V divider path into ADC.
- 0–20 mA shunt path into ADC.
- Resistance/RTD/thermistor divider or excitation path into ADC.
- Digital input threshold/protection path into an ATmega328 GPIO.
- Universal output connector with digital/PWM output conditioning.
- Optional test points and calibration notes.
Implementation expectations:
- Select suitable components from the Flux library.
- Add all required resistors, capacitors, connectors, protection parts, regulator, and ATmega328 support parts.
- Wire the complete schematic.
- Add Role and Role Details properties to important parts.
- Run ERC and fix schematic errors.
- Create a project document explaining the circuit architecture, mode configuration table, ATmega328 pin mapping, ADC scaling equations, firmware configuration notes, and limitations.
- After schematic validation, set up a reasonable PCB board size and stackup, place components by functional block, and prepare for routing.
Important design notes:
- Because the ATmega328 has limited ADC resolution and input range, include scaling and protection so all field signals are reduced to the MCU ADC range.
- Firmware must select the measurement mode and apply calibration/scaling formulas.
- If fully software-selectable mode switching cannot be achieved without extra analog-switch ICs, propose a simple alternative such as jumpers, resistor option links, MOSFET/discrete switching, or separate input terminals, and document the tradeoff before implementation.