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Intelligent Desk Lamp

Intelligent Desk Lamp. Sinan Farmaka Rade Kuljic Spring 2009. System. Introduction. Minimizing power consumption is an essential part of illumination systems. Power loss is inconvenient. Solution :

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Intelligent Desk Lamp

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  1. Intelligent Desk Lamp Sinan Farmaka Rade Kuljic Spring 2009

  2. System

  3. Introduction • Minimizing power consumption is an essential part of illumination systems. • Power loss is inconvenient. • Solution: Build an “Intelligent Desk Lamp” that will monitor the level of brightness on the desk and adjust itself in such a way to maintain a desired level of light. • Benefits: • Can be implemented in remote areas • Reduced power dissipation • Environmental

  4. Performance • Features: • Constant level of brightness at a working spot • 3 levels of brightness • “Intelligent” and “Standard” modes • Adjusts brightness within 5% of the desired level in less than 1 second even in cases of sudden changes of light • LCD indicator of levels of brightness & mode • No need to turn on/turn off in certain situations • Low cost device

  5. System Overview

  6. Dimmer Circuit • Based on chopped AC waveform • The chopping is accomplished by a triac which is controlled by a microcontroller • When triggered by a pulse at its gate (3), triac starts to conduct current; when the current reaches zero, triac turns off by itself • Wider chops => more brightness and vice versa

  7. Dimmer Circuit Triac’s characteristics: • L2004L3 - Littelfuse • Voltage capability: 200 V • Current capability: 4A • Average Power Dissipation: 0.3W • Sensitive gate: Igt=3 mA • Symmetric for all four quadrants, hence for unipolar pulses

  8. Microcontroller: PIC16F877A Tasks:

  9. 1. I/O Interface • Determines Mode & Level • Mode: standard/intelligent (0/1) - simple switch • Level: 3 discrete levels L1, L2, L3 – push button • Debouncing implemented by software • Displays Mode & Level • Mode: simple LED • Level: 7-segment LED display

  10. 2. Monitoring Level of Brightness • Light sensor: Panasonic AMS302 • built in optical filter for spectral response similar to that of the human eye • linear output • prop delay: 8.5 ms • optical angle: 50° • power dissipation: 40mW • A/D conversion – done by PIC internally

  11. 3. Determination of Triggering Delay • 8000 µs range of modulated width • Binomial search method • Precision within 2 µs in 13 steps (2^13 = 8192) • Search step of 65 ms • Calculation cycle 0.85 sec

  12. 4. Detection of Zero Crossings • AC line sampler: Scales down and rectifies AC line signal in order to be compatible with the PIC • PIC’s internal voltage reference module; set 200 mV • PIC’s internal analog comparator module • An interrupt is generated when a low voltage is detected (C1OUT=1)

  13. 5. Triggering the Triac • When a zero crossing is detected, a timer is set to a certain value which corresponds to the previously calculated triggering delay • On the overflow of the timer, an interrupt is initiated and PIC sends out a short pulse to its digital output which controls the triac.

  14. Microcontroller Programming • C code, CCS compiler, PIC Start Plus Programmer • Interrupts in priority order: • COMP – generated by the comparator module when a zero-crossing is detected • TIMER0 – generated when a triggering pulse has to be sent • TIMER2 – generated every 65ms for purpose of calculation the triggering delay • EXT – generated when desired level is changed by pressing the pushbutton • RB – generated when mode is changed by the switch • main() – the only purpose is initialization after powering up

  15. Power Supply • Powers PIC, the light sensor and display • Dc open circuit voltage of 5.1V • Output voltage stays within 5% of the desired level when load current varies between 0 and 30mA (in our case 30mA will be enough current to supply the PIC) • Open circuit voltage stays within 2% of the desired voltage as the dc line varies from 105 – 120 Vrms. • Ripple voltage at the output is less than 2% of open circuit voltage

  16. Power Supply • Transformer : 115V/6.3VCT (center tapped) • Rectifier : two diodes. • Filter : capacitor of 3.3 mF. • Regulator : zener diode with breakdown voltage 5.1V

  17. Power Supply

  18. Testing: Dimmer Circuit • Send short pulses to triac from function generator to determine minimum pulse width required to trigger the triac • Used a 250 Ω , 100 W resistor to mimic a bulb • Observed triac’s pin #2 • Voltage across the bulb is the missing part of the sinusoid.

  19. Testing: Dimmer Circuit Triac voltage for level L2 • Desired output observed • Voltage chopping works

  20. Testing: Sensor • Observed voltage with different RL • Desired: • ~ 0V for very dark environments • ~ 5V for very bright environments • RL =12k Ω is the best in terms of sensitivity • 0.67 V  dark • 4.22 V  bright

  21. Testing: Power Supply • Tested the power supply for Vac: 105Vrms, 110Vrms, 115Vrms; IL = 0mA, 15mA, 30mA. • The output voltage is monitored on the oscilloscope and all mentioned specifications are verified. • Varied the capacitance to minimize ripples.

  22. Testing: Power Supply • Output voltage : 5.2 V DC • Ripple of about 175 mV ~3% • Output current : 30mA

  23. Entire System Testing & Results • Hex Display • Push button, toggle switch and display interface checked • Sensor Value • LED array to display 8 bit value after ADC

  24. Entire System Testing & Results • Bulb Light levels • Both modes: • Triac output on oscilloscope for necessary time delays • Intelligent Mode: • Change of light with dark and bright environments • Re-adjustment of the voltage level (response delay) is about 1 second • Power loss • PIC, oscillator, sensor, display: ~ 86mW • Power supply: < 400mW • Triac: ~300mW • Total: < 790mW • Very high efficiency

  25. Issues • Dimmer circuit --Asymmetric triac • Sensor calibration • Interrupts’ priority • Delay Adjustments • Intelligent mode –- brightness levels re-adjustment

  26. Potential Improvements • Better sensor sensitivity • Use more sensors and take an average • Improve noise rejection using a DISO buffers in front of sensors

  27. Questions ???

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