Multi-point temperature upper limit sound and light alarm circuit based on LM324
The LM324 family of devices is an inexpensive quad op amp with a true differential input. They have some significant advantages over standard op amps for single-supply applications. The four amplifiers can operate at power supplies as low as 3.0 volts or as high as 32 volts, with quiescent current being one-fifth the quiescent current of the MC1741. The common-mode input range includes a negative supply, eliminating the need for external biasing components in many applications. Each set of operational amplifiers can be represented by the symbol shown in Figure 1. It has 5 pinouts, where "+" and "-" are the two signal inputs, and "V+" and "V-" are positive and negative supplies. End, "Vo" is the output. In the two signal input terminals, Vi-(-) is the inverting input terminal, indicating that the signal of the op amp output terminal Vo is opposite to the input terminal; Vi+(+) is the non-inverting input terminal, indicating the signal of the op amp output terminal Vo. Same phase as this input.
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