Semiconductor Sensor# Technical Documentation: DN6849 Photointerrupter
Manufacturer : PANASONIC
Component Type : Slotted Optical Switch / Photointerrupter
## 1. Application Scenarios
### Typical Use Cases
The DN6849 is a transmissive photointerrupter featuring an infrared GaAs LED coupled with a silicon phototransistor in a compact slotted package. Typical applications include:
Position Sensing & Detection
- Printers: Paper edge detection, carriage position sensing, and paper-out detection
- Copiers: Toner level monitoring and document positioning
- Industrial automation: Conveyor belt object counting and position limit switches
- Consumer electronics: Disc tray position detection in optical drives
Rotary Encoding
- Motor speed monitoring in appliances and industrial equipment
- Tachometer applications requiring non-contact rotation sensing
- Encoder wheels for precise angular position measurement
Object Presence Verification
- Vending machines: Product dispensing verification
- Security systems: Door/window status monitoring
- Medical devices: Cassette presence detection in analyzers
### Industry Applications
- Office Equipment : High-volume printing/copying systems requiring reliable paper path monitoring
- Industrial Control : Factory automation systems needing robust position feedback
- Consumer Electronics : Cost-sensitive applications requiring compact optical sensing
- Automotive : Non-critical position sensing in climate control and seat positioning systems
### Practical Advantages and Limitations
Advantages:
- Non-contact operation : Eliminates mechanical wear, ensuring long-term reliability
- Fast response time : Typical rise/fall time of 3μs enables high-speed detection
- Compact form factor : 4.7mm slot width accommodates various flag designs
- Environmental resistance : Stable performance across industrial temperature ranges (-25°C to +85°C)
- Electrical isolation : Complete galvanic separation between emitter and detector circuits
Limitations:
- Contamination sensitivity : Dust accumulation in slot can degrade optical performance
- Alignment criticality : Requires precise mechanical mounting for optimal performance
- Ambient light susceptibility : May require shielding in high-brightness environments
- Limited sensing distance : Effective only for objects passing directly through slot
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Inadequate Current Limiting
- Problem : LED degradation from excessive forward current
- Solution : Implement series resistor for I_F ≤ 50mA (absolute maximum)
- Recommendation : Operate at 20mA typical for balanced performance/lifetime
Pitfall 2: Poor Mechanical Alignment
- Problem : Reduced CTR (Current Transfer Ratio) from misaligned optical path
- Solution : Use precision mounting fixtures with ±0.5mm positional tolerance
- Implementation : Incorporate alignment pins in PCB design
Pitfall 3: Ambient Light Interference
- Problem : False triggering from external light sources
- Solution : Add physical shrouding or use pulsed operation with synchronous detection
- Alternative : Select models with built-in daylight filters
### Compatibility Issues with Other Components
Microcontroller Interface
- Voltage level matching : Phototransistor output requires pull-up to microcontroller VCC
- Current sinking : Ensure microcontroller I/O can sink phototransistor saturation current
- Noise immunity : Add RC filtering (10kΩ + 100nF) for electrically noisy environments
Power Supply Considerations
- LED driver compatibility : Compatible with standard GPIO (3.3V/5V systems)
- Supply decoupling : 100nF ceramic capacitor near device recommended
- Transient protection : TVS diodes suggested for industrial environments
### PCB Layout Recommendations
Component Placement
- Maintain minimum 2mm clearance from high-speed digital lines
- Position away from heat-generating components (>5mm from power devices)
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