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Adjust the trimming potentiometer R3 to move the needle of ammeter PA1 to the maximum value on the scale. The pin out diagram works any any style 74xx or 74xx DIP chip, but the timing graphs are only valid for the TTL families indicated.

744121 pulse voltage is proportional to the input frequency, through the diode VD5 this voltage charges the capacitor C1.

or Timer as a One-Shot

The ammeter PA1 indicates the voltage across the capacitor C1. There are two different methods of connecting Rx and Cx. The Figure 1 shows the circuit diagram of the frequency meter, the circuit based on the digital IC Note the uses a 4k internal resistor, while the uses a 20k resistor.

The first method for a Cx of less than pF [below] and a second connection [below that] for an external capacitor, Cx, of greater than pF. Turn the rotary switch S1 of the frequency meter to the range of Hz and connect the device to the reference signal source of Hz. All this allows to create very simple frequency meter circuit with several frequency ranges: A quartz crystal oscillator circuit that can generates kHz signal with a 3-stage decade counter can be used as a reference frequency source see the Figure 2.


This IC is the monostable multivibrator that may generate a pulse of a different width from 35 ns and wider that depends on RC components. This device uses the ammeter with full-scale deflection of 0.

Frequency meter with 74121 monostable multivibrator

Also refer to Transistor Multivibrator Circuits. Do the same operation for all ranges.

C5 and trimming potentiometers R All this allows to create very simple frequency meter oc with several frequency ranges:. The device can measure sinusoidal wave and square wave input signals. The Diodes used in the circuit are 1N or equivalent.

Frequency meter with monostable multivibrator Digital integrated circuits can be used in the design of an analogue frequency meter with a frequency range to several MHz.

How to calibrate this frequency meter? Reference oscillator circuit diagram. The two graphs below show the resultant pulse width for different values of iv and capacitors. You’ll need a source of stable frequency reference signal that can produces a set of frequencies Hz, 1 kHz, 10 kHz and kHz.

  IEC 61209 PDF

The pulse frequency depends on the input frequency. The first chart works for either the 74L or 74L; however, the second chart only applies to the 74L By the way, the ammeter PA1 can be replaced with a digital multimeter.

Frequency meter with monostable multivibrator

How to Read Logic Truth Tables: The circuit could be used for any TTL family, such as LS, or H, but the load capacitor might need to be changed to reflect that. To use the internal timing resistor connect Rint to Vcc. Digital integrated circuits can be used in the design of an analogue frequency meter with a frequency range to several MHz. A Monostable Multivibrator is also called a One Shot. The load Capacitance CL is 50pF, including scope probe, wiring, and any stray capacitance.

Electronic Engineering Dictionary

The pulse width produced by the monostable multivibrator depends i the values of capacitors C While the shown below provides a retriggerable Monostable Multivibrator function with clear.

The number of frequency ranges can be increased by using a rotary switch SA1 with more than four positions, and by adding some additional RC components.

VD4 protects the integrated circuit from overloading. Instead ofthe SN or DM can be used. The shown above provides a single Monostable Multivibrator function.