frequency counter using opto isolator

Reply Fri 1 Feb, 2013 11:44 am
here I am trying to design an analog project which counts the frequency.circuit consist of an photo transistor opto isolator and some counters for counting number of cycles per second.For this 1 second i am using timer ic(555).Now my doubt is which phototransistor opto isolator should I use inorder to count frequency till 16 Khz.As above 16Khz i would require prescalar.thanking you in advance
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Reply Fri 1 Feb, 2013 12:27 pm
All you need to do is check out the specification sheet. Any and all electronics distributors supply them.

More info can be found here:


"American guitar and organ manufacturers of the 1960s embraced the resistive opto-isolator as a convenient and cheap tremolo modulator. Fender's early tremolo effects used two vacuum tubes; after 1964 one of these tubes was replaced by an optocoupler made of a LDR and a neon lamp.

To date, Vactrols activated by pressing the stompbox pedal are ubiquitous in the music industry. Shortages of genuine PerkinElmer Vactrols forced the DIY guitar community to "roll their own" resistive opto-isolators.

Guitarists to date prefer opto-isolated effects because their superior separation of audio and control grounds results in "inherently high quality of the sound". However, the distortion introduced by a photoresistor at line level signal is higher than that of a professional electrically-coupled voltage-controlled amplifier. Performance is further compromised by slow fluctuations of resistance owing to light history, a memory effect inherent in cadmium compounds. Such fluctuations take hours to settle and can be only partially offset with feedback in the control circuit."


"Opto-isolators can be too slow and bulky for modern digital applications. Since the 1990s, researchers have examined and perfected alternative, faster and more compact isolation technologies. Two of these technologies, transformer based isolators and capacitor-coupled isolators, reached the mass market in the 2000s. The third alternative, based on giant magnetoresistance, has been present on the market since 2002 in limited quantities. As of 2010, production models of all three types allow data transfer speeds of 150 Mbit/s and resist voltage transients of up to 25 kV/μs, compared to 10 kV/μs for opto-isolators. Unlike opto-isolators, which are stacks of discrete LEDs and sensors, the new devices are monolithic integrated circuits, and are easily scalable into multi-bit data bus isolators."
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Reply Fri 1 Feb, 2013 12:59 pm
Rash12 wrote:
Now my doubt is which phototransistor opto isolator should I use inorder to count frequency till 16 Khz

A simple 4N32 will fit your requirement.

4N32 datasheet
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