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CD4011

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• Logic gates form high-impedance voltmeter
  You can use the circuit described in this Design Idea to estimate voltages across 10- to 100-MΩ resistances. It also works for reverse-biased diodes. The common CMOS gates in Figure 1 have an input threshold voltage in which the output swings from logic zero to logic one, and vice versa. The threshold voltage depends on the supply voltage (Figure 2). Because of each CMOS gate’s high input impedance, input currents are approximately 0.01 nA. If you apply 5 V to 100 MΩ, you get ...
• Analog-to-digital frequency-dependent relays
  Mikhail Shustov, Tomsk The operation principle is described and the diagrams of analog-digital frequency-dependent relays, whose switching occurs when the certain setting valuation input frequency is exceeded by frequency, are given. Analog-digital frequency relays, considered in the article, are designed to respond to the executive or indicating device to exceed the specified limit value by the predetermined threshold controlled frequency. The undeniable advantage of such relays is that they ...
• Use LEDs as photodiodes
  The simple circuit in Figure 1, which can be powered with a 3.6 V nickel-cadmium rechargeable battery, lets you use an LED to detect light. The circuit consumes practically no quiescent power. Two LEDs act as photodiodes to detect and respond to ambient light. When ambient light is present, the upper LED, a small, red, transparent device covered with a black pipe, has a higher effective resistance than the lower, large, green LED. The voltage drop across the input of the NAND gate is less than ...