IC 74121 PDF

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

All this allows to create very simple frequency meter circuit with several frequency ranges: This device uses the ammeter with full-scale deflection of 0. 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. Note the uses a 4k internal resistor, while the uses a 20k resistor. A Monostable Multivibrator is also called a One Shot.

The shown above provides a single Monostable Multivibrator function. The pulse voltage is proportional to the input frequency, through the diode VD5 this voltage oc the capacitor C1. All this allows to create very simple frequency meter circuit with several frequency ranges:. The Diodes used in the 71421 are 1N or equivalent.


The load Capacitance CL is 50pF, including scope probe, wiring, and any stray capacitance. Do the same operation for all ranges.

Frequency meter with 74121 monostable multivibrator

To use the internal timing resistor connect Rint to Vcc. Instead ofthe SN or DM can be used. 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. The pulse frequency kc on the input frequency. VD4 protects the integrated circuit from overloading.

Electronic Engineering Dictionary

While the shown below iv a retriggerable Monostable Multivibrator function with clear. 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.

Reference oscillator circuit diagram. The first method for a Cx of less kc pF [below] and a second connection [below that] for an external capacitor, Cx, of greater than pF. 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. The two graphs below show the resultant pulse width for different values of resistors and capacitors.

The first chart works for either the 74L or 74L; however, the second chart only applies to the 74L The ammeter PA1 indicates the voltage across the capacitor C1.

Turn the rotary switch S1 of the frequency meter to the range of Hz 7121 connect the device to the reference signal source of Hz.


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. C5 and trimming potentiometers R The device can measure sinusoidal wave and square wave input signals. Adjust the trimming potentiometer R3 to move the needle of ammeter PA1 to the maximum value on the scale.

The Figure 1 shows the circuit diagram of the frequency meter, the circuit based on the digital IC You’ll need a source of stable frequency reference signal that can produces a set of frequencies Hz, 1 kHz, 10 kHz and kHz. 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.

How to calibrate this frequency meter?

Frequency meter with monostable multivibrator

There are two different methods of connecting Rx and Cx. Also refer to Transistor Multivibrator Circuits. Digital integrated circuits can be used in the design of an analogue frequency meter with a frequency range to several MHz. How to Read Logic Truth Tables: The pulse width produced by the monostable multivibrator depends on the values of capacitors C

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