30-Khz Bandwidth High Linearity Opto-Isolated Amplifier

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 we use similar devices with similar non-linearity error characteristic. A […]

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555 IC’s Hysteresis for Dark Activated Relay

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 darkness level for activating and deactivating the relay will be […]

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Logarithmic Light Intensity Meter for Photography

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 point of conversion slope at ±18°C temperature drift. It should […]

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Laser Diode Driver

A  laser diode driver can be implemented using voltage-controlled current source.  This simple  linear laser diode driver gives cleaner drive current than a switched (PWM) drivers. Here is the schematic diagram of the circuit: A Howland current pump with a current booster is used as the basic of this laser diode driver. Q1 is used as the current booster on […]

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