← All projects
Arduino Mega 12V I/O Expander
ATmega2560 board with sixteen level-shifted 12 V outputs, thermal cutoff protection and active fan control.
- ATmega2560
- PCB Layout
- Thermal Design
- Altium Designer
Problem
Applications driving many 12 V peripherals need a high channel count at industrial voltage levels from one compact, self-contained board.
System overview
A dense custom PCB around the ATmega2560. An array of dual-BJT level shifter stages translates 5 V logic into 12 V switched outputs, broken out as four screw terminal banks (J2–J5) with dedicated 12 V and GND rails per group — sixteen independently controllable outputs for solenoids, indicators and relays. An LM35 sensor drives an automatic power cutoff on overtemperature, a MOSFET stage drives a cooling fan, and an onboard OLED/LCD module gives local readout.
Responsibilities
- Schematic and layout of the level-shifter array and power section
- Thermal protection and closed-loop fan control design
- Firmware for output control, thermal cutoff and local display
Hardware architecture
- ATmega2560 with onboard USB-to-TTL programming header
- 16× dual-BJT 5 V → 12 V level-shifted outputs across J2–J5
- LM35 analog temperature sensor plus digital temperature header
- MOSFET fan driver on the H6 FAN/GND header
- OLED/LCD status module, SPI expansion header, 12 V input with onboard 5 V regulation
Firmware architecture
- Independent control of 16 output channels
- Thermal monitoring with automatic regulator cutoff above threshold
- PWM or on/off fan control tied to the thermal loop
- Local status readout on the onboard display
Communication interfaces
- SPI
- UART (USB-to-TTL)
- Analog / 1-Wire temperature
- PWM
Engineering challenges
- Routing sixteen level-shifter stages and their terminal banks on a compact board
- Thermal headroom under sustained load, solved with sensed cutoff plus active cooling
Hardware & diagrams
