IC 74121 PDF

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Frequency meter with 74121 monostable multivibrator

The pulse frequency depends on the input frequency. Instead ofthe SN or DM can be used. The load Capacitance CL is 50pF, including scope probe, wiring, and any stray capacitance.

There are two different methods of connecting Rx and Cx. 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. Also refer to Transistor Multivibrator Circuits.

Note the uses a 4k internal resistor, while the uses a 20k resistor. The first chart works for either the 74L or 74L; however, the second chart only applies to the 74L The Diodes used in the circuit are 1N or equivalent.

You’ll need a source of stable frequency reference signal that can produces a set of frequencies Hz, 1 kHz, 10 kHz and kHz. All this allows to create very simple frequency meter circuit with several frequency ranges: To use the internal timing resistor connect Rint to Vcc.


The pulse width produced by the monostable multivibrator depends on the values of capacitors C VD4 protects the integrated circuit from overloading. The pulse voltage is proportional to the input frequency, through the diode VD5 this voltage charges the capacitor C1.

All this allows to create very simple frequency meter circuit with several frequency ranges:. A Monostable Multivibrator is also called a One Shot. Digital integrated circuits can be used in the design of an analogue frequency meter with a frequency range to several MHz.

The device can measure sinusoidal wave and square wave input signals. C5 and trimming potentiometers R Do the same operation for all ranges. This device uses the ammeter with full-scale deflection of 0. The circuit could be used for any TTL family, such as LS, or H, but id load capacitor might need to be changed to reflect that.

Frequency meter with monostable multivibrator

Adjust the trimming potentiometer R3 iic move the needle of ammeter PA1 to the maximum value on the scale. How to calibrate this frequency meter? The pin out diagram works any any style 74xx or 74xx DIP ix, but the timing graphs are only valid for the TTL families indicated. The shown above provides a single Monostable Multivibrator function. The ammeter PA1 indicates the voltage across the capacitor C1. The two graphs below show 744121 resultant pulse width for different values of resistors and capacitors.


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. While the shown below provides a retriggerable Monostable Multivibrator function with clear. Reference oscillator circuit diagram.

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.

A quartz crystal oscillator circuit that can generates kHz signal with ix 3-stage decade counter can be used as a reference frequency source see the Figure 2.

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. How to Read Logic Truth Tables: The Figure 1 shows the circuit diagram of the frequency meter, the circuit based on the digital IC 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.

By the way, the ammeter PA1 can be replaced with a digital multimeter.