Voltage comparators like the LM311 do this with high accuracy, fast response, and minimum external component count. The output will go high or low, depending on set-up, as the sensor voltage goes above or below the reference.
The other is used to measure the target signal, such as the voltage on a sensor. Usually, this is done by using a voltage divider to produce a known voltage, and then feeding it to one of the inputs. Op-amps have many other modes of operation, but the comparator is the one relevant to this article. Op-amps can be arranged as a comparator, where one input is compared to the other and the output goes high or low depending on the situation in the inputs. In single rail situations, a synthetic ground is arranged. Op-amps are often driven from a positive and negative split rail power supply with a zero volt ground in the middle, allowing them to operate negatively or positively. One input is inverting and the other is non-inverting, which means that a positive voltage on the inverting input will cause a negative voltage on the output, and a positive voltage on the non-inverting input causes a positive voltage on the output. Operational amplifiers are an IC with high-impedance inputs which means they are voltage-sensitive rather than current-sensitive. Of course, not every reader will be familiar with op-amps or previous articles, so here is a very brief recap. However, the LM311 Integrated Circuit (IC) is a dedicated device which does only this job, and does it well. We’ve previously come across the comparator before when discussing Operational Amplifiers (Op Amps), and we have even made them out of op-amps in projects. Comparing voltages or switching at a threshold can be done with the Analog to Digital Converter (ADC) built into Arduino and Raspberry Pi, but we will discuss later some very valid reasons why you may want to do this externally. This IC is a low-component-count way to compare two signal voltages or a signal and a reference, and switch the output either on or off.Ĭomparators do a very specific job that presents some advantages to the maker which may not be immediately obvious.
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