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I have designed a simple and efficient zero-point acquisition circuit, and everyone gives me some suggestions.

MCU
September 24, 2020 by Alma 1778

The zero-point acquisition function has been used for many years in the industry. The practice has always been to directly introduce the AC signal current limit into the IO with low requirements; use a triode for higher requirements; use transport to make 0V comparisons for higher requirements. I recently thought of a circuit, and suddenly found that no matter how high the zero point acquisition requirements are, it can be so simple. The method is to use two IOs to bias to Schmidt's upper and lower threshold voltages (0.7Vcc and 0.3Vcc for stm8s microcontroller) according to the Schmitt characteristics of IO input, and then superimpose the input AC signal to be near 0V Trigger IO level jump. The specific circuit is shown in the figure below:

IO_H is connected to rising edge to collect IO, IO_L is connected to falling edge to collect IO, and the acquisition is triggered by an external interrupt mode.

All Comments

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Salma Posted on September 24, 2020

This transition time should not be the real zero-crossing "point", the output is an interval, it depends on the accuracy of the zero-crossing time of your specific application.

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Ralph Posted on September 24, 2020

Isn't it right, why is the output an interval? IO_H only takes the rising edge to trigger the interrupt, IO_L only takes the falling edge to trigger the interrupt, and both of these trigger points are in a critical state when the AC is at 0V.

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Gerald Posted on September 24, 2020

The setting of 0.7Vcc and 0.3Vcc itself is a kind of hysteresis. If your two ports are inconsistent state, how to deal with it.

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Ezequiel Posted on September 24, 2020

The port biased at 0.7Vcc only detects rising edges, and the port biased at 0.3Vcc only detects falling edges. The status of the two ports is different near the zero point. When the rising edge occurs, the 0.7Vcc port first detects the rising edge, and then the 0.3Vcc port detects the rising edge (this port ignores the rising edge); when the falling edge, the 0.3Vcc port first detects the falling edge. Detect the falling edge after 0.7Vcc port (this port ignores the falling edge).

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