Making light intensity measuring table using LM3915 comparator ----- LM3915 Light Meter

Keywords: LM3915, light intensity measurement This article describes a strength circuit for measuring light, as shown in the drawings. It can be at different light levels, such as minimal, medium and larger. Displays the linearity of the light. The circuit uses a PN junction photodiode as a photoelectric sensor and a display driver IC LM3915. The display driver can turn the energy of the incident light into a linear scale. The photodiode has a high frequency 晌 晌 晌 and the NS level switching speed. The "N" material of the photodiode is made of a monophonium doped phosphorus. To generate free electrons; "P" material is boron boron boron to form free holes. night. A saturated current is formed in the photodiode. Under the light. Generate free electrons. The linear photodance generated on the photodiode is proportional to the light weight. The typical photocurrent is 10 Pa to 90μA / 5V. The radiation sensitivity of the PN junction light diode is 0.4ua ~ 4ua / mW / cm2. Circuit. The photodiode takes a forward bias through the current limiting resistor R1 to the power source. To form an optical current. The photocurrent flows through the preset VR1 (potentiometer) to the input of IC1 5 foot. The interior of the IC1LM 3915 is embedded in the accompanying drawings to indicate the variable voltage in the drawing. When IC1 input pin 5 receives the incremental change of 1.25V, the LED starting from the (18) of IC1 will be lit to the right, because the inside of IC1 has a comparator with ten current sources and by Gradient voltage divider formed by the basic reference voltage. The 7 pin of the IC1 holds the voltage of 1.25V (reference voltage), and the resistor R2 controls the lighting current through each LED. If the potentiometer VR2 is adjusted, the first LED1 can first light, and then adjust the potentiometer VR1. The input voltage of the IC1 can be adjusted to light the LED7. Such LED1 indicates the weakening light, LED4 (yellow) indicates that medium intensity light and LED 7 indicate the brightness of normal light. The capacitor C1 can be slightly delayed when the LED is lit and the LED is performed slightly. It can be seen from the above-described debugging process: When VR2 and VR1 are adjusted, it is carried out under normal brightness conditions to ensure that the intensity of the light indicates sufficient. Because the average person does not illuminate the ambient light, only the feeling of the eyes (natural state) is subject to the sensation. Installing the circuit on a small printing board. Plug in a small box. When the installation is complete, the VR1 should be adjusted to slide the VR2 in a clockwise direction (maximum). Note: This circuit cannot work under the fluorescent lamp, which cannot detect a single color spectrum due to photodiodes.

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