NE555 timer sparks low-cost voltage-to-frequency converter

In 1971, Signetics—later Philips—introduced the NE555 timer, and manufacturers are still producing more than 1 billion of them a year. By adding a few components to the NE555, you can build a simple voltage-to-frequency converter for less than 50 cents. The circuit contains a Miller integrator based on a TL071 along with an NE555 timer (Figure 1). The input voltage in this application ranges from 0 to –10V, yielding an output-frequency range of 0 to 1000 Hz. The current of C1 is the function of input voltage: IC=–VIN/(P1+R1).

NE555 timer sparks low-cost voltage-to-frequency converter

As the voltage on C1 reaches two-thirds of VCC, the 555’s internal discharge transistor opens, and the voltage on C1 returns to one-third the voltage of VCC, the lower comparator threshold. At one-third this voltage, the discharge transistor switches off, and C1 again starts charging. The NE555’s output is high while C1 is charging and low while C1 is discharging. The product of the input voltage and the charging time of C1 is constant. Because the discharge time is shorter than the charging time, the following equation results for the output frequency: fOUT~VIN/(P1+R1)×C1×1/3VCC.

P1 calibrates the relationship between the output frequency and the input voltage. Because the discharge interval is approximately 30 µsec, the accuracy of the voltage-to-frequency conversion decreases as the frequency increases.

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Ibrar Ayyub

I am an experienced technical writer holding a Master's degree in computer science from BZU Multan, Pakistan University. With a background spanning various industries, particularly in home automation and engineering, I have honed my skills in crafting clear and concise content. Proficient in leveraging infographics and diagrams, I strive to simplify complex concepts for readers. My strength lies in thorough research and presenting information in a structured and logical format.

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