Common Light Emitting Diodes (LEDs) require a DC forward bias current of 10 to 20 mA for proper operation. Typically the maximum DC current is 30 to 50 mA. The color of light (or wavelength ») emitted from an LED depends on the semiconductor material used to fabricate the LED and this in turn determines the LED forward voltage at the operating cu
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rrent. The forward voltage, which is roughly equal to the semiconductor bandgap potential of the active material in the LED is about 1 V for infrared LEDs with » ~ 880 - 920 nm such as those used in consumer remote-control devices, 1. 8 V for red LEDs at » ~ 660 nm, 2. 2 V for green LEDs at » ~ 560 nm and 3V for white LEDs. Infrared LEDs are available with analog modulation bandwidths of kHz to 20 MHz and higher. The circuits below demonstrate two basic approaches for analog current modulation of LEDs. The first circuit is useful for modulation up to about 5 MHz and uses a single transistor circuit biased as a firm current source with the LED in the collector circuit. With the circuit components shown, the high frequency cutoff is about 4 - 5 MHz, limited by the base-emitter forward biased capacitance. The quiescent DC current through the LED as determined approximately by (Vcc/2 - 0. 7)/R5 or about 24 mA. The low frequency cutoff frequency is about 15 Hz. The output current modulation amplitude in midband is approximately Vs/R4. A 100 mV modulation input provides a current modulation of 10 mA. The second circuit is useful up to about 50 MHz and uses a high-frequency analog op amp, a Linear Technology LT1363 with a GBW of 70 MHz, a slew-rate of 1000 V/us and an output current drive capability of at least 50 mA: The circuit is a transconductance or voltage-to-current converter configuration. The output is DC biased using a...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
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The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
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In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
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