Idea to build simple frequency meter from old calculator

This circuit use a simple ideal is the calculator count a frequency within range 1 second.
This time base is generated by IC-555,on astable multivibrator form.

How it works

The number on the calculator’s panel is the input frequency. to base of transistor Q2 .
The capacitance of C1 should is lowest tolerance,to be accurate.
But this circuit can measure frequency: 250MHz maximum only, because the Q2 feature. If need to counts higher frequency, you can change number of Q2.

Idea to build simple frequency meter from old calculator

For example the 2N2369 transistor, can measure frequency about 500 MHz.
Also,we should choose the good calculator to measure high frequencies. This circuit use the casio version VL-1.

How to adjust and uses

This is very easy to adjust. First, set calculator to ready, start to press 1 button, then press + + (press plus button) 2 times, next press “=”, then press “+”, press “-”, and lastly press “=”, until the number show as 0 or zero.

Second, apply the reference frequency to this at base of Q2 for example frequency 100 Hz, then adjust VR1 until can read to 100, may be long time. Just this we will have simple frequency meter.

Importance! This is ideal only I cannot tell you this worked.
When uses we should apply the input frequency in to base of Q2 before, then select switch S1 to the circuit.

Sharing is caring!

Related Posts


I always try to make Electronics Learning Easy.

JLCPCB - Only $2 for PCB Protytpe(Any Color)

With 600,000+ Customers Worldwide, 10,000+ PCB Orders Per Day

Up to $20 shipping discount on first order now:

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

newest oldest most voted
Notify of

fanstastic idea.


hey thanks for the posts. any help with 4017 and triac to regulate fan speed project thanks.


Hi! Perfect work thanks for de post any help for a mosfet. Based pure sinewave circuit diagram


Please what do you mean by terminal


Hi. About frequency meter circuit with calculator.
1. How high is the peak-to-peak voltage?
2. Where does the calculator connect?
3. Should the signal input be connected to the terminal or to the in
4. Can this cordless telephone frequency range in the range of approximately 400 megahertz be measured?

Thank you.

Close Menu