Fill factor meter. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Fill factor meter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Measuring technology

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In the practice of a radio amateur, measuring the duty cycle or duty cycle may be necessary when establishing or checking various nodes of pulse technology, auto electronics, etc. The proposed device is assembled on a microcontroller and measures the duty cycle of the pulse period in percent. It should be recalled that the duty cycle S is the ratio of the repetition period T (repetition) of pulses of one sequence to their duration m. The reciprocal of the duty cycle is called the duty cycle D: S \u1d T / τ \u2d 0,5 / D. Frequent use in practice finds a signal with S = XNUMX or D = XNUMX - a meander.

The device displays the duty cycle in the range from 1 to 99% with a resolution of 1%, the error in the middle of the interval is 1 ... 2%. The frequency range of the input pulse signal is from 4 Hz to 40 kHz and can be extended up to 100 kHz, the signal amplitude is from 1 to several tens of volts. The calculation of the filling factor in percent is carried out in accordance with the expression D = 100τ/T. The algorithm for measuring the pulse duration and period is based on counting the pulses of the microcontroller clock generator using a 16-bit timer-counter TC1. To expand the measurement range and ensure their accuracy, the frequency of the pulses received at the input of the timer-counter TC1, if necessary, is reduced by a frequency prescaler by 64 times. This happens if, during the period of the input pulse signal, an interrupt occurs due to the overflow of the counter-timer TC1. If this does not happen, the frequency prescaler is turned off and the timer-counter TC1 receives pulses directly from the clock generator of the microcontroller.

If the frequency of the input signal is less than the lower limit of the operating frequency range, the symbols "Lo" are displayed on the indicator, if more than the upper - the symbols "Hi", both for the range up to 40 kHz, and for the range up to 100 kHz.

Duty Cycle Meter

The meter circuit is shown in the figure. The basis of the device is the ATtiny2313 microcontroller, which operates according to the program, the codes of which are given in Table. 1. It performs all the necessary calculations and displays information on the LED two-digit indicator in the dynamic indication mode. Since long-term stability of the microcontroller clock generator is not required, a built-in RC oscillator operating at a frequency of 8 MHz is used, which simplifies the device circuit. On the transistor VT1, a node for matching the input signal levels with the logic levels of the microcontroller is assembled, which is necessary when measuring signals with different amplitudes. Diode VD1 protects the emitter junction of transistor VT1 from breakdown when an alternating or pulse signal of negative polarity is applied to the input. The supply voltage of the microcontroller is stabilized by the DA1 microcircuit stabilizer.

Duty Cycle Meter

The printed circuit board was not developed, all parts are mounted on a breadboard using wired wiring. Resistors MLT, C2-23 are used, oxide capacitors are imported, C3 - K10-17. The voltage regulator LM7805 can be replaced with KR142EN5A. Indicator A-402G-10 - on two separate seven-element LED indicators with a common anode, by combining the outputs of the same elements, and common anodes, connecting to the emitters of the transistor VT2 or VT3 (lower-order anodes are connected to VT2). You can power the device with a voltage of 9...12 V from an unstabilized power supply, the current consumption depends on the displayed values and does not exceed 60 mA.

Duty Cycle Meter

If the microcontroller is set to work from a generator with an external quartz resonator at a frequency of 20 MHz, by connecting it according to the standard scheme, the upper limit of the operating frequency range will increase to 100 kHz. The device readings were checked using an APPRA-107M digital multimeter, which has a built-in fill factor meter.

The adjustment device is not required. When programming the microcontroller, the configuration bits are set in accordance with Table. 2. For a generator with a 20 MHz quartz resonator, they are given in Table. 3.

The program for the microcontroller can be downloaded hence.

Author: V. Nefedov, Bryansk; Publication: radioradar.net

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