Design a circuit that detects the presence of the infrared signal. The circuit should light a red LED when infrared signal is detected otherwise it should light a green LED. You may use NPN transistors, IR LED, Photodiode, Red LED, Green LED and a rectifier diode.

This project involves designing a portable device that can inject a 1kHz sine wave signal into a 100V audio line to detect short circuits. The device should be compact (around the size of a smartphone) and include LED indicators to show the status: a green LED for normal operation and a red LED for short-circuit detection. The device will be powered either by a switching power supply or rechargeable batteries.

makes a circuit which has transistors, diodes, relays, IC Timer, LED, which first turns on a green LED lit from 0 to 35 degrees Celsius then turns off and turns on a yellow LED from 35 degrees Celsius to 50 degrees Celsius then turns off the yellow and turns on the red at 50 degrees or more which in turn will turn on an oscillator circuit with IC555 and a Buzzer. In addition it should turn on an exhaust fan at 110 VAC. Translated with DeepL.com (free version)

64-position 1206 green LED array using Digi-Key-sourced in-stock SMD LEDs.

Analog water-level controller using an LM31 liquid level sensor input and PEL00884 brushed DC motor drive. The circuit buffers and scales the ratiometric sensor signal, derives motor current demand versus water level, shuts the motor off at 100%, and lights a green full-tank LED.

Resonate Pendant golden reference design. Board is a 39 mm x 63 mm portrait rectangle with 5 mm corner radii, 2-layer FR4, 0.8 mm thickness, 1 oz copper on both layers, matte black top solder mask, no bottom solder mask, ENEPIG finish, and no silkscreen on either side. Allowed components only: U1 STM32L052C8T6, U2 CH340E, U3 BQ24210DQCT, C1 10uF, C2 4.7uF, C3-C7 100nF, R1 24k, R2 1k, R3 10k, D1 green 0402 LED, MAG1-MAG4 magnetic pads, J1 solar solder pads, J2 battery solder pads, TP1-TP4 test pads. Required top artwork: golden-ratio grid lines and gold circles on F.Cu with mask openings, decorative only, 0.8-1.0 mm width, at least 0.5 mm from active traces. Required bottom artwork: exposed ENEPIG bottom copper split into FREQ_OUT 61.8 percent and GND 38.2 percent with an exact 0.20 mm S-curve isolation gap, no vias through bottom except one PA4-to-FREQ_OUT via at the extreme edge. Functional requirements: MAG1 and J1 VIN feed U3 IN, U3 OUT feeds J2 battery pad and system VBAT, MAG2 to U2 UD+, MAG3 to U2 UD-, MAG4 to common ground, U2 TX to U1 PA10, U2 RX to U1 PA9, U1 PA4 to bottom FREQ_OUT, U1 PA5 to R2 then D1 to GND, U3 ISET to R1 to GND, U3 TS to R3 to GND, decoupling exactly as specified. Prohibited items: external crystal, JST connectors, wireless module, antenna, separate regulator IC, ESD protection IC, USB-C connector, through-hole parts, bottom solder mask, silkscreen, more than three ICs, or any unapproved substitutions.

I want make a board that trigger a green and red LED with three wire, 0V, 24V and output of proximity switch. but i want output wire remain 0V when not connected.

Red, Green, Blue (RGB) 623nm Red, 530nm Green, 472nm Blue LED Indication - Discrete 1.9V Red, 2.7V Green, 2.8V Blue 0404 (1010 Metric)

Greenhouse controller with temperature and humidity control Input voltage 12v led voltage: 12v humidifier voltage: 5V Display: i2c 0.96 OLED display sensor: htu21d i2c