Here’s how you can spot a fake ATmega328P – a commonly counterfeited microcontroller, especially in Arduino-compatible boards:

1. Visual Inspection (ATmega328P)
Markings:

• Genuine chips have clean, crisp laser markings or printing.
• Fakes may show blurry text, incorrect fonts, or an outdated/fake Atmel or Microchip logo.

Suspicious Date Codes:

For example, a chip marked with a 2024 date under the Atmel brand is suspicious, since Microchip acquired Atmel in 2016.

Package Anomalies:

• Surface may show sanding or grinding (to re-label an old chip).
• Unusual finish (too shiny, too matte, or inconsistent with genuine chips).

2. Functional Testing
Bootloader Issues:

• Bootloader flashing may fail.
• Programming via Arduino IDE may be unreliable or only work at 8 MHz (instead of 16 MHz).

Unstable Behavior:

• EEPROM errors.
• Resets or crashes when power-cycled.

Signature Mismatch:

Use avrdude or similar tools to read the chip signature.

bash

avrdude -c usbasp -p m328p

Expected signature:

java

Device signature = 0x1e950f

Fake chips may return incorrect or inconsistent signature bytes.

3. ISP Programming Problems

• May have incorrect fuse bits.
• Could refuse to lock/unlock properly.
• Show strange behavior on SPI or other low-level protocols.

4. Electrical Behavior

• Higher-than-expected power consumption.
• Overheating even when idle.
• Unstable at lower voltages (e.g., under 5 V).

5. Supply Chain Checks
Always buy from:

• Authorized distributors: Digi-Key, Mouser, Farnell, Arrow, Ampheo, etc.
• Trusted Arduino-certified vendors for official boards.

Avoid:

eBay, AliExpress, or other marketplace sellers offering very low prices or "bulk chips" with no traceability.

6. Community Knowledge
Many counterfeit reports involve:

• Relabeled chips (e.g., ATmega8 or ATmega48 being sold as ATmega328P).
• Chips requiring modified bootloaders to work at all.

You can check:

• EEVblog Forums
• Reddit /r/arduino
• Arduino forums for part number and batch discussions.