IC 74121 PDF

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Frequency meter with monostable multivibrator

The load Capacitance CL is 50pF, including scope probe, wiring, and any stray capacitance. This IC is the monostable multivibrator that may generate a pulse of a different width from 35 ns and wider that depends lc RC components.

The ammeter PA1 indicates the voltage across the capacitor C1. 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. VD4 protects the integrated circuit from overloading. 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. 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.


or Timer as a One-Shot

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. You’ll need a source of stable frequency reference jc that can produces a set of frequencies Hz, 1 kHz, 10 kHz and kHz. Note the uses a 4k internal resistor, while the uses a 20k resistor. Adjust the trimming potentiometer R3 to move the needle of ammeter PA1 to the maximum value on the scale.

Electronic Engineering Dictionary

The two graphs below show the resultant pulse width for different values of resistors and capacitors. The pulse voltage is proportional to the input frequency, through the diode VD5 this voltage charges the capacitor C1. Instead ofthe SN or DM can be used.

There are two different methods of connecting Rx and Cx. While the shown below provides a retriggerable Monostable Multivibrator function with clear.

To use the internal timing resistor connect Rint to Vcc. C5 and trimming potentiometers R The pin out diagram works any any style 74xx or 74xx DIP chip, but the timing graphs 7121 only valid for the TTL families indicated.

Reference oscillator circuit diagram. The Figure 1 shows the circuit diagram of the frequency meter, the circuit based on the digital IC This device uses the ammeter with full-scale deflection of 0.

The pulse frequency depends on the input frequency. All this allows to create very simple frequency meter circuit with several frequency ranges: By the way, the ammeter PA1 can be replaced with a digital multimeter. The device can measure sinusoidal wave and square wave input signals. The first chart works for either the 74L or 74L; however, the second chart only applies to the 74L The shown above provides a single Monostable Multivibrator function.


All this allows to create very simple frequency meter circuit with several frequency ranges:. 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.

The Diodes used in 741221 circuit are 1N or equivalent. How to calibrate this frequency meter? Digital integrated circuits can be used in the design of an analogue frequency meter with a frequency range to several MHz. Turn the rotary switch S1 of the frequency meter to the range of Hz and connect the device to kc reference signal source of Hz. The pulse width produced by the monostable multivibrator depends on the values of capacitors C A Monostable Multivibrator is also called a One Shot.

How to Read Logic Truth Tables: Do the same operation for all ranges.