|
|
|
|
|
|
|
|
|
|
|
Simple
Frequency Meter |
|
|
|
|
|
Figure 1.
Frequency Meter Circuit Diagram
This circuit
is a frequency meter, i.e., it measures the frequency of the input
signal in terms of current passing through an ordinary ammeter.
The main
component of this circuit is the 555, a versatile, general-purpose timer
IC. In this circuit, the 555 is configured as a monostable multivibrator
that outputs a single pulse at pin 3 every time the input signal at pin
2 goes 'low'.
The width of
the output pulse generated by the 555 is defined by R3 and C3. The
larger the output pulse width, the longer is the time that pin 3 is
high. Since pin 3 doesn't sink current when it is high, the current
passing through the ammeter is higher when pin 3 is high. This
means that the larger the values of R3 and C3 are, the larger is the
output pulse width, and the higher is the current passing through the
ammeter for a given input frequency.
For any given
value of R3 and C3, on the other hand, the current passing through the
ammeter increases as the input frequency increases. This is
because pin 2 is 'retriggered' more often as the input frequency
increases, decreasing the total duration wherein the output is 'low'.
Thus, the ammeter dial in this circuit would be a good indicator of the
relative frequency of the input signal at pin 2.
Good choices
for the values of R3 and C3 to match the intended application as well as
careful
calibration through R5
are required
to make this simple circuit work properly.
See
also: 555 Monostable
Multivibrator
Go
Back to the PROJECTS Menu
HOME
|
|
|
|
|
|
|
