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 Posted: Jun 25, 2012 - 12:52 PM |
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Joined: Jun 04, 2012
Posts: 304
Location: Mumbai,India
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there is a problem occur in my design. the resistive divider does not ensure an isolation.i dont want to use transformer(for saving placeand cost).
can i use optocoupler? is optocoupler is able to give a voltage fluctuation? |
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Posted: Jun 25, 2012 - 01:10 PM |
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Joined: Jul 18, 2005
Posts: 62922
Location: (using avr-gcc in) Finchingfield, Essex, England
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Quote:
is optocoupler is able to give a voltage fluctuation?
No. |
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Posted: Jun 25, 2012 - 01:43 PM |
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Joined: Jun 04, 2012
Posts: 304
Location: Mumbai,India
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if so i have a doubt Mr.clawson
if the input of the optocoupler vaies between 180-260v then the light emitting from the diode varies which limit the o/p voltage. is it true? |
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Posted: Jun 25, 2012 - 06:13 PM |
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Joined: Jan 07, 2012
Posts: 1312
Location: North of France
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Well, 160-260 volts seem very dangerous.
Perhaps your initial idea of a transformer was a good one (if you want AC sampled with some realism: how can you do with optocouplers, which are very nonlinear if voltage signs change -they vary between -260 and 260 volts, do not they ?)
Perhaps it would be wise to try first testing some code , first trying a channel, with a continuous low voltage supply: when your code will work, addding 2 other channels and trying to be as close as possible to your final data processing (and the idea of what you want to do) would be very useful to you, and keep you alive.
Therefore Mr Bobgardner gave you valuable (perhaps even life saving) advices three posts before. |
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Posted: Jun 27, 2012 - 06:17 AM |
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Joined: Jun 04, 2012
Posts: 304
Location: Mumbai,India
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| can i use o/p of full bridge rectifier as input to adc in atmega168 |
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Posted: Jun 27, 2012 - 07:15 AM |
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Joined: Jan 08, 2009
Posts: 1198
Location: Lund, Sweden
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| Yes, as long as the voltage is in valid range, which usually means within -0.5V -- Vcc+0.5V (those are absolute maximum ratings). |
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Posted: Jun 27, 2012 - 09:08 AM |
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Joined: Jun 04, 2012
Posts: 304
Location: Mumbai,India
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thanx snigelen
actually i want to sense the line voltage using resister
drop method and there is no isolation.i dont want to use transformer because i need a small device. |
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Posted: Jun 27, 2012 - 10:10 AM |
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Joined: Jan 08, 2009
Posts: 1198
Location: Lund, Sweden
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| I wouldn't mess with unisolated line voltage or recommend anyone to do it. It can kill people or burn down the house if something goes wrong. |
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Posted: Jun 27, 2012 - 11:52 AM |
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Joined: Sep 04, 2002
Posts: 21390
Location: Orlando Florida
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| How about a small transformer? There are some the size of a walnut at Skycraft. |
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Imagecraft compiler user
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Posted: Jun 27, 2012 - 12:06 PM |
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Joined: Jun 04, 2012
Posts: 304
Location: Mumbai,India
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i think the bridge give isolation. actually in my circuit ,i drop the 230 V to less than 1V and given to bridge.and output(unregulated dc) of that bridge to input pin of adc.
actually i'm worriying about the unregulated dc?is this unregulated dc consider as a analog signal? |
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Posted: Jun 27, 2012 - 12:26 PM |
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Joined: Jan 07, 2012
Posts: 1312
Location: North of France
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A bridge (rectifier) does not give isolation, it just rectifies the two waves of the mains (and, if you hold [with damp hands]a card connected with the mains, you might be killed or shocked).
A transfo does give isolation, without the non linearities of an optocoupler (if your resistive voltage divider divides down to ca 1v, you are likely in a very non linear region of its internal IR LEDs; perhaps your optocoupler has a name, and even an application note google can find). |
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Posted: Jun 27, 2012 - 12:33 PM |
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Joined: Jun 04, 2012
Posts: 304
Location: Mumbai,India
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| im not going to use optocoupler. what about a transistor bias for taking the linearity? |
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Posted: Jun 27, 2012 - 01:04 PM |
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Joined: Jan 07, 2012
Posts: 1312
Location: North of France
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Can your design be drawed (use kicad, inkscape, gimp, tuxpaint or {scan|put into your CDreader} a pencil and paper schema and post it) It is very difficult to figure out what you want to do with the mains and it seems dangerous?
Did you test your adc conversion routines, and did they work (this is less dangerous than playing with the mains!) ?
Did you code your data processing, and test it with values you know a solution for? |
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Posted: Jun 27, 2012 - 01:13 PM |
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Joined: Jun 04, 2012
Posts: 304
Location: Mumbai,India
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no, im not test it.
the only thing confuse me is is a un regulated dc (o/p of bridge)act as a input to adc.are you try it? |
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Posted: Jun 27, 2012 - 01:44 PM |
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Joined: Jan 07, 2012
Posts: 1312
Location: North of France
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I did not try anything, because
a) if your hardware (I cannot figure out what it is) is connected to the mains, it can be dangerous and I do not want to commit suicide.
b) if ***your*** unregulated dc goes above the supply of the avr (or becomes negative, with poor wiring), it would kill the avr.... and it would be annoying.
FYI I usually test with a voltmeter http://de.wikipedia.org/wiki/Voltmeter unregulated dc s I buy, before using them....
And your software works so well it does not need being tested? |
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Posted: Jun 30, 2012 - 12:37 PM |
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Joined: Jun 04, 2012
Posts: 304
Location: Mumbai,India
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| is their any need for external capacitor(oscillator) for using 1MHz system clock? |
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Posted: Jun 30, 2012 - 01:39 PM |
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Joined: Sep 04, 2002
Posts: 21390
Location: Orlando Florida
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| Maybe on the aref pin depending on how much ripple in the power supply. |
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Imagecraft compiler user
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Posted: Jul 04, 2012 - 12:52 PM |
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Joined: Jun 04, 2012
Posts: 304
Location: Mumbai,India
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| Can i give regulated bridge o/p as Vcc to atmega series? |
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Posted: Jul 04, 2012 - 12:59 PM |
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Joined: Jan 07, 2012
Posts: 1312
Location: North of France
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a) What is the value of your regulated bridge output?
b) Is it really regulated (post a photo or the schematics if you do not know)?
c) Is it above the value you want to measure (I dare to remember it was your initial topic) and within the admissible range of your atmega (you may have 200 volt regulated)? |
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Posted: Jul 04, 2012 - 01:38 PM |
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Joined: Jun 04, 2012
Posts: 304
Location: Mumbai,India
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| no, its from 7805 fixed regulator. for Vcc |
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