Project Name: Smoke Alarm

Project Details: PCB Cloning, BOM Compilation, Reverse Engineering of Schematics

Client: Guiyang

Project Features: Finding Alternative Transistors Based on Codes

Smoke alarms can be found in many places, such as kitchens and high-rise buildings. They typically require a few dry batteries. The principle behind optical smoke alarms involves an optical maze with an infrared receiver connected to it. When there is no smoke, the infrared receiver does not detect the infrared light emitted by the infrared transmitter. However, when smoke particles enter the optical maze, the infrared receiver detects the infrared light through refraction and reflection. The intelligent alarm circuit then determines if the signal exceeds the threshold, triggering an alarm if necessary.

The client came across our services online and sent us a sensitive smoke alarm with a unique feature set, including:

• Short or continuous beep modes
• Alarm memory function
• Sensitivity control time: 9 to 12 minutes
• I/O filters and charge release
• Capability to interconnect up to 40 detectors
• Internal power-up reset
• All pins have ESD protection (>2000V HBM)
• Low static current (<8 μA)

The PCB was relatively simple, but during the BOM compilation, we encountered some transistors with only code markings, and we couldn't find specific part numbers online. Fortunately, we provided the client with a schematic diagram, which allowed their engineers to find a suitable longer IC (Integrated Circuit) as a replacement. The PCB file was slightly modified, swapping the connections between pins 2 and 3. This successful substitution resolved the issue.