Siricinco Semiconductor

Smoke, Gas and Carbon Monoxide three-in-one Sensor

Brief Introduction of the Scheme

Sensor technology is constantly developing in the direction of high precision, low power consumption, and miniaturization. Most traditional home security devices are single-function products (only smoke alarms or only gas alarms). Users need to purchase and install multiple devices, which is costly and complex to maintain. All-in-one composite detectors are becoming the mainstream direction of the industry-integrating smoke detection, CO detection, and gas detection into one device to achieve comprehensive protection, accurate identification, and effectively reduce false positives. At the same time, alarms are evolving from stand-alone devices to intelligent networked types, supporting functions such as remote monitoring, APP alarms, and linkage with smart home platforms. This solution uses the SK88Fx78 series as the main control chip.

The system clock supports up to 16MHz and is compatible with the MCS-51 instruction set.

● The core advantage of the chip is the highly integrated analog front end (AFE), which is specially designed for smoke detector applications. Two operational amplifiers for optical signal detection

● Sinking current generator with integrated constant current output (Range 50mA~360mA), can directly drive LED light sources

● Dedicated gas/CO AFE: Built-in 1 operational amplifier for signal detection of gas or CO detectors

● Built-in 12-bit SAR ADC (up to 12 external)

● Built-in RTC real-time clock (Support digital calibration, accuracy 0.95ppm)

● Built-in temperature sensor (accuracy ±2℃) SK88Fx78 series integrates all traditional optical detection front-end circuits that require multiple discrete components into a single chip. It can complete all functions such as smoke light source driving, signal processing, alarm indication, and clock calendar.

Working Principle

System Architecture

Core Advantage

● Three-in-one detection capability-on-chip 3-channel operational amplifiers (2 smoke AFE+1 gas/CO AFE)+1 external operational amplifier, covering signal conditioning of smoke, gas, and CO sensors, meeting the needs of three-in-one alarm

● Built-in LCD driver-hardware LCD/LED driver Support 8COM×16SEG (maximum 128 segments), optional duty cycle 1/4 to 1/8, directly drive segment code LCD screen, no need for external LCD driver IC

● Ultra-low standby power consumption- STOP mode only 1.0μA (@5V), LCD can continue to drive and display in STOP mode

● High-precision smoke detection- 12-bit ADC+ dedicated smoke dual op amp, support single or dual optical path (red light + blue light) solutions, multi-spectral analysis accurately distinguishes smoke from water vapor, dust, etc. Interference sources

● High-sensitivity gas/CO detection-On-chip dedicated op amp is matched with semiconductor/catalytic combustion sensors (gas) or electrochemical sensors (CO), The signal link is specially optimized for weak signal amplification

● Intelligent temperature compensation-Built-in ±2℃ temperature sensor compensates for the impact of environmental temperature drift on the three sensors in real time to avoid false positives; Wide temperature operation of-40℃~85℃

● Constant current LED driver-Built-in 50mA~360mA adjustable constant current sink current generator, directly drives infrared/blue LEDs without external constant current source circuits

● Flexible communication interconnection- 3 sets of UART (up to 1Mb/s)+I2C+SPI, can be directly connected to RF/Bluetooth/Zigbee modules, Achieve networking and interconnection

● Complete alarm and recording- RTC (0.95ppm accuracy)+31.5KB FLASH

● Complete power management-Level 8 LVD (1.8~4.4V) accurately monitors battery power to achieve low power warning; Level 4 LVR (1.7~4.3V) prevents voltage fluctuations from causing system abnormalities

● Safety and easy development- 96-bit unique UID supports product traceability;2-wire simulation interface facilitates online debugging;WDT watchdog ensures long-term stable operation

● Principle of photoelectric detection

This scheme is based on the principle of scattered light/transmitted light to detect smoke, fully complying with the technical requirements of GB 20517-2025 for photoelectric detection.Inside the optical maze, the emitting light path and the receiving light path form a certain angle (usually an obtuse angle). Under normal working conditions, the receiving end can hardly detect optical signals. When smoke particles enter the maze, the emitted light scatters on the surface of the particles, and some of the scattered light is captured by the photosensitive device at the receiving end. The higher the smoke concentration, the greater the scattered light intensity.

Photoelectric detection signal chain:

① Constant current drive: The MCU's built-in current generator (adjustable from 50mA to 360mA) provides a constant driving current for the LED, ensuring consistent light intensity and avoiding power fluctuations that affect measurement.

② Signal reception: The photosensitive device converts the scattered light received into a weak current signal.

③ Amplification and conditioning: The current signal is input into a dedicated operational amplifier (smoke AFE) built into the MCU, and after I/V conversion and voltage amplification, it is conditioned into a voltage signal suitable for ADC sampling.

④ Analog to digital conversion: The amplified signal is sent to a 12 bit SAR ADC and converted into a digital signal for MCU processing.

● Intelligent discrimination and anti-interference

① Temperature compensation

The built-in temperature sensor (with an accuracy of ± 2 ℃) compensates in real-time for the impact of environmental temperature changes on the optical path and circuit, avoiding false alarms caused by temperature drift.

② Dual optical path enhancement technology

For scenarios with higher anti-interference requirements, the solution can support dual path detection of red and blue light:

Two operational amplifiers process the scattered signals of red and blue light respectively. Different wavelengths of light have different scattering characteristics on smoke particles and interference sources (water vapor, oil fume). By comparing the ratio of the two signals, the true fire smoke and interference sources can be accurately distinguished, greatly reducing the false alarm rate.

③ Pollution monitoring

Long term monitoring of the baseline value when smoke-free, if the baseline drift is caused by dust pollution, a yellow pollution alarm will be triggered.

● Low power operation

The system wakes up from STOP mode at a fixed cycle (e.g. every 10 seconds) and returns to STOP mode after completing one smoke detection. The single working time is only milliseconds, the average power consumption is extremely low, and it meets the requirements of long-term battery life. The wake-up source can come from the RTC automatic wake-up unit or external GPIO interrupts (such as buttons, infrared remote control signals).

Programme Classification

Charge Management
- Battery Charger
Fire Detection
- New National Standard Smoke Detection Alarm
- Three-in-one Hybrid Detection Alarm
Security Authentication
- Consumables Certification
Computer Peripheral
- E-sports Keyboard
- E-sports Mouse
Office Printing
- Laser Printer
- Thermal Printer