differential circuit

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mojtaba_led
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Posted by mojtaba_led: Sat. Jul 9, 2011 - 06:27 PM
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hi every body
excuse me i'dont speak english well! :oops:
if i chose incorrect suject for my prablem excuse me!
i want to detect zero crossing point of a Sinusoidal signal with this circute that see under :
i simulated in proteus and it work corectly but i don't sure that is work in fact
please help me abiut this
fils of proteus : zero_detector2.rar
and pictures :


[/url]

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Learning and Information, General Electronics
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Kas
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Posted by Kas: Sat. Jul 9, 2011 - 11:05 PM
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Looks OK.
Will possibly require input AC conditioning and input protection. Depends of the AC source, of cause.

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Bronze Markjs
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Posted by js: Sat. Jul 9, 2011 - 11:06 PM
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Quote:
i don't sure that is work in fact
Then build the circuit and try it out. Dump Proteus :)

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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mojtaba_led
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Posted by mojtaba_led: Sun. Jul 10, 2011 - 08:42 AM
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thanks for answers

Quote:
Will possibly require input AC conditioning and input protection. Depends of the AC source, of cause.

what condition and protection?

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valusoft
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Posted by valusoft: Sun. Jul 10, 2011 - 09:46 AM
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mojtaba_led wrote:
thanks for answers
Quote:
Will possibly require input AC conditioning and input protection. Depends of the AC source, of cause.

what condition and protection?
Depends upon the AC condition/specifications. If it is 230 VAC 50Hz you will need a different approach compared with if it is 5 VAC.

Ross McKenzie, Melbourne Australia

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mojtaba_led
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Posted by mojtaba_led: Sun. Jul 10, 2011 - 10:52 AM
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thank you
no it can be 1mv ac to 5v ac i'm using a transformer and a resistor divider to scale down in Interval 0 to 5 vac

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ka7ehk
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Posted by ka7ehk: Sun. Jul 10, 2011 - 04:08 PM
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At 1mv, you will have problems as many comparators have an input offset of several millivolts. You will need a comparator with less than 1mv offset. An LM324 will not meet that spec.

Be careful about the input voltage range. I don't believe that a LM324 will handle 5V AC input with +/-5V supplies. And, are those voltages RMS or peak?

Its not clear what the function of the two buffers is. Any micro input will handle the clipped comparator output just fine without the buffers.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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mojtaba_led
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Posted by mojtaba_led: Sun. Jul 10, 2011 - 08:02 PM
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thank you very much for answer

Quote:
are those voltages RMS or peak?

those are peak

Quote:
Its not clear what the function of the two buffers is.

i used these to receive better pulse whitout Distortion
and the first gate is 40106 that is a shmit triger not and the second gate is 4009 that is a not

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ka7ehk
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Posted by ka7ehk: Sun. Jul 10, 2011 - 08:46 PM
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This circuit will NOT work so well. An LM324 is an op-amp, not a comparator. If you use a comparator with an open-collector output, such as an LM339, you won't need that terrible diode network. Simply connect the output transistor's emitter to ground. You also will not need the Schmitt trigger and the other buffer.

However, almost all of these low-cost comparators and op-amps have offset voltages as high as 3mV (sometimes larger). This means that the signal must be at least 3mv in order to trip the comparator, and better 6mV.

Jim

 

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jayjay1974
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Posted by jayjay1974: Sun. Jul 10, 2011 - 09:28 PM
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I guess the diode network and caps are to create spikes on each zero-crossing. Not really required as the MCU can handle that.

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