Tag Archives: Optoelectronics

Logarithmic Light Intensity Meter for Photography

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Using LM10 amplifier and voltage reference, a light intensity meter featured with five decades dynamic range (which is suitable for photographic application) can be built.  Please note that the linear to log conversion is not temperature compensated, and can make 40% error (a half stop in photography) at the worst… Read more »

555 IC’s Hysteresis for Dark Activated Relay

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In the relay’s  point of view, dark activated means the relay will be activated when the  light intensity fall below a certain threshold.   Without hysteresis, the relay will be activated and deactivated if the sensed brightness fall under or rise above a single point of darkness level. With hysteresis, the… Read more »

30-Khz Bandwidth High Linearity Opto-Isolated Amplifier

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Using optocoupler to directly transfer a linear (analog) voltage would produce  a large unpredictable linearity error, which is also sensitive to temperature changes. By using frequency modulation, the total system’s linearity will  depend only on the linearity of the V/F and F/V converter, which is fortunately cancel each other if… Read more »

Very Simple Light Meter

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Very simple light meter can be constructed using LDR (light dependent resistor)  wired in series with a battery, variable resistor, and  ampere meter. Here is the schematic diagram of the circuit: The ampere meter is a 100 uA analog meter. Don’t expect too much about the linearity, absolutely can’t be… Read more »

Solid State Relay (SSR) with Optocoupler and Triac

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This solid state relay (SSR)  equivalent circuit is made of optocoupler and a triac. This SSR circuit is also designed with  LED protection from overvoltage and reverse polarity. The diode 1N4002 is the reverse polarity protector, as it will short the wrong polarity to null the voltage with the help… Read more »

General Infrared Remote Controlled Relay

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This relay circuit is controlled by almost any type of infrared remote controller. This circuit works on assumption that almost all remote controller use high frequency modulated infrared light. By filtering out un-modulated or low frequency modulated signal, this circuit will be able to remove any interference from ambient infrared… Read more »

Flash-Triggered Pulse Stretcher Using Classic Monostable Circuit

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This is a flash triggered (photo-driven) circuit which produce a pulse with constant predetermined wide. This circuit can be used to control any device which is required to be synchronized with optical trigger/flash light.  The pulse can be used to drive relay (after proper power buffering,  to drive other circuit… Read more »