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# How to attenuate a square wave signal?

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#### jimbobjones

##### Newbie level 2
Hello i'm new to the forum.

I need to attenuate a square wave signal from 5v pk to 3v pk.

Is this possible with an opto coupler ?

if not what else can i use?

voltage divider ? or will this corrupt the signal.

The signal is a 5v pk square wave maxF = 50hz generated by an analogue IC that i want to interface with a microcontroller that operates at 3v.

aplitude

you want a 74ls07 open collector buffer. on the o/p pin use a 10K or so pull-up resistor tied to 3V.

I am assuming the signal's lowest voltage is 0V.

Re: square wave aplitude

If your squarewave is from 0V to 5V then you can use simple resistor voltage divider composed of 2.2k and 3.3k resistors.

Re: square wave aplitude

Borber said:
If your squarewave is from 0V to 5V then you can use simple resistor voltage divider composed of 2.2k and 3.3k resistors.

It depends where the square wave is coming from. That sort of resistive loading could cause problems in numerous circuits.

Re: square wave aplitude

It was said that signal comes out of analog IC. Sink and source currents for analog ICs are greater than 1mA.

Re: square wave aplitude

Sorry I missed the part about the analogue IC.

A voltage divider will work for such a low frequency if there is plenty of current available.
It would be necessary to check that the input resistance of the pin and take it into consideration when picking the values for the divider.

An o/c buffer will provide a more stable and guaranteed (high)voltage level, which will not be sensitive to changes in loading at any input pin. The buffer will however increase the total power consuption of the system, but not by much.

Re: square wave aplitude

Input resistance of MCU is much higher than 3.3k and in the case that port is just sensing logical levels precision is not a problem at all. Only a precaution that MCU pin voltage is within allowed range is necessary.

Re: square wave aplitude

thats for the help

i'll use a voltage divier before an optocoupler (for isolation)

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