Thank you a lot Manifold :)

Best regards,
Refa

--- In Electronics_101@yahoogroups.com, "manifold" <manifold_1@y...>
wrote:
> You do not need paste to hand solder a SMD. Solder paste is used in
> the manufacture of PCB's. The paste is silk screened on to the
> component pads where each component is placed. Then the entire
board
> goes through a special heat cycle that melts all the solder at once.
>
> Hand rework of SMD board just requires a good iron, a steady hand
and
> lots of practice. Here are some tips that I find useful:
>
> Use a fine gauge solder and a temperature controlled soldering
iron.
> Do not use a super fine or super long soldering iron tip. It takes
> too long for heat to move through them. Use a small (1/16" - 1/8")
> blunt screwdriver tip instead. Use sturdy tweezers to hold the
parts.
> Use the back, sticky side, of a post-it(tm) note to keep parts from
> blowing off your work space.
>
> Here is a quick procedure:
> Put a tiny bit of solder on the PCB pad of the component to be
> soldered. Position the part and heat the pad and component lead so
> that it "tacks" the component down at one lead position. Now solder
> all the other leads. Go back and clean up the "tack" joint made
> earlier.
>
> Once you get the hang of it it's a lot easier and faster than
> soldering leaded parts. Of course there are a lot more parts on
> boards now too.
>
> --- In Electronics_101@yahoogroups.com, "integrodev"
> <integrodev@y...> wrote:
> > Dear group,
> > I have a question for those who work with SMD components.
Probably
> > many of you use hot air soldering stations but what do you do if
> you
> > have just old irons. I heard a paste exists and you put it and
> after
> > some minutes it leads current normaly? Can anybody tell me how
much
> > these pastes cost and where I can find them? Give me some
solutions
> > how your solder senstive SMDs. Thank you
> >
> > Best regards,
> > Refa

 

Well thank  you for your input.  That's unfortunate =(

Is there any way to get around that?

Well, there are things you can do with the circuit itself that may
be more important than the physical layout of your board.

Some considerations are:
Voltage, current, and frequency.

If your circuit uses only <12v, has only IC components and no high
frequency on it, you can lay things out pretty close to any way you
damn well please and it won't make any difference.

Fat traces are needed for higher currents but you'd probably be
amazed at just how many amps a skinny little trace can handle. Check
the net for trace width calculators.

Wide traces are much more important for high frequency circuits
because of the way electrons behave under high frequency. They tend
to stay away from the inner portions of the copper and travel around
the outer layers - effectively making your trace much smaller.
Wider/thicker traces are required.

Frequency also dictates spacing of traces. You don't want a low
power analog trace running beside a high-frequency trace because it
will introduce a lot of noise to the analog portion. Remember,
traces are basically little radio antannae. The electric current
sets up magnetic fields around every trace - if the current changes,
so do the magnetic fields and you induce currents into nearby
traces. In low frequency digital circuits, this induced noise isn't
very critical but if you use analog circuits they can make the whole
thing useless.

The convention is to have each layer's traces run perpendicular to
the other. Top layer left/right and bottom up/down. This is
generally easier for laying out but it also has a practical side. An
analog trace crossing a digital one at right angles will pick up
very little noise compared to running parallel to one another.

Digital chips tend to use power in bursts. For example, a PCF8574
not being used consumes a miniscule amount of power. As soon you
communicate with it the power consumption jumps to a couple
milliamps. This sudden change in current will cause the radio-
transmitter effect as described above. If you put a bypass capacitor
between the power and ground pins (as close to the chip as possible)
the capacitor then supplies this current instead of your voltage
regulator. Only the trace between the cap and the chip has large
changes in current, making a short radio transmitter. Current
changes between the cap and the voltage regulator are much smaller,
making for a far weaker transmitter. This also helps smooth out
noise on the power leg of your circuit.

Another goal for layout is separate electron paths back to the
ground leg of your regulator. Each device on a ground trace will
introduce noise into that trace. The noise can affect how the
devices operate. Again, digital is far more tolerant than analog but
digital also generates a lot more noise. Its pretty well mandatory
that you use seperate ground traces for digital and analog
components. While daisy chaining digital device grounds is usually
no problem, analog devices are a lot more finicky. Where possible,
give each one its own trace back to the regulator. Which brings us
to the next topic:

Ground planes help a LOT in ground noise. It does so in two ways:

1) Since electrons flow like water - taking the path of least
resistance, a ground plane effectively separates the ground current
for each device, reducing the impact of each chip on the others.

2) It absorbs RF interferance - reducing induced noise in the
circuit.


--- In Electronics_101@yahoogroups.com, "c45a6" <clone45@h...> wrote:
>
> Hello!  I'm fairly new to doing PCB designs, and I'm working on a
> little circuit board that I may someday sell.  I'm using
ExpressPCB
> to manufacture the boards.
>
> My question is, what are some rules of thumb to follow when
designing
> a PCB?  For instance, I found out that I should avoid right angles
on
> skinny traces, and that I should use wide (greater than .05 in)
> traces for power and ground.
>
> I've noticed that other PCBs have large ground squares where
there's
> room.  Is that good practice?
>
> Is it best to put most of your traces on the top or bottom layer?
>
> Thanks a ton!
> - Bret

Has anyone seen any good Freeware PCB Design, I was using AutoTrax EDA but
it's auto router sucks and making anything is horrid. I also had used that
Express PCB but you can only send it into Express PCB to get made..

Anyone have something they think is real easy?

rofl, I don't think I'm up to that but thank you nonetheless Tony.

> Yes, but it is a little complicated. You have to detect the pulses
during the blanking period as this is where the protection is
applied. The contrast and brightness signals are dependent on the a
part of this blanking, the protection mucks this up. They are
therefore fluctuating because the video recorders AGC can't keep up
with the changes. I have seen a circuit in an electronics magazine
here in Australia if you are interested in building it.
> Tony
>
>   Well thank  you for your input.  That's unfortunate =(
>
>   Is there any way to get around that?

----- Original Message -----

From: Vijay Raju

To: Electronics_101@yahoogroups.com

Sent: 8/1/03 7:04:25 AM

Subject: [Electronics_101] 230V AC as i/p to a uC

Hi,

 

            I am using the ckt in the attachment to detect 230V AC arriving on an output of an industrial PLC. I am trying to step down the voltage to 5V so my microcontroller can recognize the presence or absence of 230V. Now the problem is that the ckt seems to hold charge for really long times. i.e. if I remove the 230V input for a couple of minutes the output of the MCT2E is low. The second problem is that the output of the MCT2E is varying only between 4 and 5V. i.e 4V at 230V and 5V at 0V. What could be causing these problems?

 

 

Regards,   

 

                     ,,,

                    (@-@)

        +==---o00----(_)----00o-----==+

        {                             |

        {        Thoughts from        |

        {         Vijay  Raju         |

        {                             |

        +==-------------------------==+

                   |__|__|

                    || ||

                   ooO Ooo

 

 

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Electronics_101-unsubscribe@yahoogroups.com



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----- Original Message -----

From: Philip K. Panicker

To: Electronics_101@yahoogroups.com

Sent: 7/30/03 6:00:03 PM

Subject: [Electronics_101] Isolation problem

Thanks Scotty, you are absolutely right. I have sort
of a 'MacGyver' like kind of problem. I have to use
the equipment available to me in my lab at the
university. I am actually trying to build an ion
detector known as a Langmuir probe. I am using a
single probe that is biased with a 1 Hz +-50V
sawtooth.
I do have a 4 channel 2GS/s 8 bit digitizing HP
O'scope available. So far I was using the time base
mode, but I can use the differential mode also.
I do not have the sawtooth oscillator built so far. I
was initially thinking of building a square wave
generator with a 555 connected to a capacitor to get
the sawtooth. However, now I am thinking of using a
regular Function Generator signal input through an
optocoupler to an amplifier of some sort to get +-50V,
so that the ground can be isolated.
The nA can be translated to 100s of mV range, since
the O'scope can safely detect down to 1mV. I am
thinking this way, I won't introduce too much noise
from bigger resistors in the opamp ckts. I am not too
good with advanced electronics, so I have to read up
on what chopper stabilized power supply means. I am
thinking it has got something to do with switch mode
power supplies.
Thanks for your help. It is helping me learn things
that I would never have seen in the text books.
Philip


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rofl, I don't think I'm up to that but thank you nonetheless Tony.

> Yes, but it is a little complicated. You have to detect the pulses
during the blanking period as this is where the protection is
applied. The contrast and brightness signals are dependent on the a
part of this blanking, the protection mucks this up. They are
therefore fluctuating because the video recorders AGC can't keep up
with the changes. I have seen a circuit in an electronics magazine
here in Australia if you are interested in building it.
> Tony
>
>   Well thank  you for your input.  That's unfortunate =(
>
>   Is there any way to get around that?



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Hi,

  you can also try "Eagle", they have a freeware program for schematic
and pcb design
(for private use) or you can subscribe for a small donation to get the
professional version.
There is a Windows and Linux version available. See   www.cadsoft.de for
all info.

                 Cheers Albert.



Charles Douvier wrote:

> Has anyone seen any good Freeware PCB Design, I was using AutoTrax EDA but
> it's auto router sucks and making anything is horrid. I also had used that
> Express PCB but you can only send it into Express PCB to get made..
>
> Anyone have something they think is real easy?
>
>
>
> Yahoo! Groups Sponsor
> ADVERTISEMENT
> click here
>
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51838331032>
>
>
>
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>
>
>
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> <http://docs.yahoo.com/info/terms/>.

There are a few steps depending on the PC end of the job.

First write the PIC code to read/write EEPROM

Second, write the PIC code to read/write USART.  Select baud rate,
data format, etc.

Third, develop a command structure such that the PIC knows what the
PC expects it to do.  Could be as simple as W<addr><value><CR> or
R<addr><CR> to write and read eeprom.  Write the PIC code to
implement the command structure calling the EEPROM and USART code as
required.

Assuming the PIC is busy doing better things, the USART code and
command code will probably need to be interrupt driven.  It may turn
out that the interrupt routine validates the command sentence and
sets up a flag for the command routine to deal with the received data.

You will also have to handle the issue of a data stream arriving
faster than the PIC can handle.  One way is with echo - the sending
party doesn't send a future char until the present char has been
echoed.

Fourth, develop a PC program using whatever tools you have to send
the commands and retrieve the results, storing them in a file.

Your message from the PIC to the PC may want to include some version
of the original command so that the PC can verify that it got the
data it asked for.  Maybe the return message is D<addr><value><CR>.

If you are REALLY concerned about the data then maybe a checksum is
added to all messages like: W<addr><data><checksum><CR> or
R<addr><checksum><CR> or D<addr><data><checksum><CR>.

That's pretty much it.

--- In Electronics_101@yahoogroups.com, "Paul_Lav" <paul_lav@y...>
wrote:
> Hi,
>
> We have a control board at work. It is a microproceossor. There is
a RS232 connector on the board to download/upload EEPROM values. They
are stored in a .txt file on the PC. How would i go about doing this
for a pic microcontroller?
>
> Thanks,
> Paul

I have made a frequency Counter.. in which I have used a Frequency
devider IC # HC7496 TTL IC  which stops working when the frequency
goes above 2 MHz Range.. Have some one any Idea why????????

Help is required urgently

Ali Shamshad
Pakistan

Looking for these parts in small qty from a distributor in the
U.S.A.:

Circuit board "Vero" style (39 copper strips x 62 holes per strip)

ICL7673 (battery backup watchdog chip)

NEC 431000 32 pin, 1MBit, 8 bit, low power CMOS SRAM chip
or
628128 (made by Hitachi)
or
K6T1008C2E (made by Samsung)
or comparable 1MBit sram

Regards,
Paul

----- Original Message -----

From: rtstofer

To: Electronics_101@yahoogroups.com

Sent: Saturday, August 02, 2003 3:34 PM

Subject: [Electronics_101] Re: Storing EEPROM of a PIC onto a PC

There are a few steps depending on the PC end of the job.

First write the PIC code to read/write EEPROM

Second, write the PIC code to read/write USART.  Select baud rate,
data format, etc.

Third, develop a command structure such that the PIC knows what the
PC expects it to do.  Could be as simple as W<addr><value><CR> or
R<addr><CR> to write and read eeprom.  Write the PIC code to
implement the command structure calling the EEPROM and USART code as
required.

Assuming the PIC is busy doing better things, the USART code and
command code will probably need to be interrupt driven.  It may turn
out that the interrupt routine validates the command sentence and
sets up a flag for the command routine to deal with the received data.

You will also have to handle the issue of a data stream arriving
faster than the PIC can handle.  One way is with echo - the sending
party doesn't send a future char until the present char has been
echoed.

Fourth, develop a PC program using whatever tools you have to send
the commands and retrieve the results, storing them in a file.

Your message from the PIC to the PC may want to include some version
of the original command so that the PC can verify that it got the
data it asked for.  Maybe the return message is D<addr><value><CR>.

If you are REALLY concerned about the data then maybe a checksum is
added to all messages like: W<addr><data><checksum><CR> or
R<addr><checksum><CR> or D<addr><data><checksum><CR>.

That's pretty much it.

--- In Electronics_101@yahoogroups.com, "Paul_Lav" <paul_lav@y...>
wrote:
> Hi,
>
> We have a control board at work. It is a microproceossor. There is
a RS232 connector on the board to download/upload EEPROM values. They
are stored in a .txt file on the PC. How would i go about doing this
for a pic microcontroller?
>
> Thanks,
> Paul



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Electronics_101-unsubscribe@yahoogroups.com



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----- Original Message -----

From: Vijay Raju

To: Electronics_101@yahoogroups.com

Sent: Friday, August 01, 2003 11:54 PM

Subject: RE: [Electronics_101] 230V AC as i/p to a uC

Hi,

 

Thanks! Initially I was trying to do the same thing trying to drop the voltage across a large resistor. But things were getting hot and ugly. The idea here is to use the reactance of the cap to drop the voltage. In fact I got this idea from a microchip app note (www.microchip.com/download/appnote/pic16/91008b.pdf)

 

I have a good amount of time about 500 ms to detect a change over. I just want to know how to get the time constant right.

 

 

Regards,

 

                     ,,,

                    (@-@)

        +==---o00----(_)----00o-----==+

        {                             |

        {        Thoughts from        |

        {         Vijay  Raju         |

        {                             |

        +==-------------------------==+

                   |__|__|

                    || ||

                   ooO Ooo

----- Original Message -----

From: alishamshad2000

To: Electronics_101@yahoogroups.com

Sent: Saturday, August 02, 2003 10:27 PM

Subject: [Electronics_101] Frequency Devider IC not working over 2 MHz in a frequency Counter

I have made a frequency Counter.. in which I have used a Frequency
devider IC # HC7496 TTL IC  which stops working when the frequency
goes above 2 MHz Range.. Have some one any Idea why????????

Help is required urgently

Ali Shamshad
Pakistan



To unsubscribe from this group, send an email to:
Electronics_101-unsubscribe@yahoogroups.com



Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.

did u look up the data sheet of the ic?

manoj

----- Original Message -----

From: alishamshad2000

To: Electronics_101@yahoogroups.com

Sent: Saturday, August 02, 2003 10:27 PM

Subject: [Electronics_101] Frequency Devider IC not working over 2 MHz in a frequency Counter

I have made a frequency Counter.. in which I have used a Frequency
devider IC # HC7496 TTL IC  which stops working when the frequency
goes above 2 MHz Range.. Have some one any Idea why????????

Help is required urgently

Ali Shamshad
Pakistan



To unsubscribe from this group, send an email to:
Electronics_101-unsubscribe@yahoogroups.com



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On the subject of transformers.
Does anyone know where I could find a matrix of the various types of
transformers and their functions?
I know of power transformers. But what about inverter transformers? How many
different kinds of  transformer are there?

MAG

----- Original Message -----

From: ali shamshad

To: Electronics_101@yahoogroups.com

Sent: Monday, August 04, 2003 6:42 PM

Subject: Re: [Electronics_101] Frequency Devider IC not working over 2 MHz in a frequency Counter

thank you for reply .i dont have data sheet ,send me if you or any one have and another

IC   LM3364K

Manoj Cherukat <manojc@...> wrote:

did u look up the data sheet of the ic?

manoj

----- Original Message -----

From: alishamshad2000

To: Electronics_101@yahoogroups.com

Sent: Saturday, August 02, 2003 10:27 PM

Subject: [Electronics_101] Frequency Devider IC not working over 2 MHz in a frequency Counter

I have made a frequency Counter.. in which I have used a Frequency
devider IC # HC7496 TTL IC  which stops working when the frequency
goes above 2 MHz Range.. Have some one any Idea why????????

Help is required urgently

Ali Shamshad
Pakistan



To unsubscribe from this group, send an email to:
Electronics_101-unsubscribe@yahoogroups.com



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---

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hi all
          looking for a circuit diagram for my philips CD 960 cd
player ! havebeen having problem with the cd draw for some time and
now it wont open at all !would be pleased to hear from anyone who
has any ideas
regards ron

  ronb28@...

Hmm, that questions is a little like asking how many different kinds
of circuits there are.

If by inverter transformers you mean those that are used in
Uniterruptable Power Systems (UPS) then there are a few different
types but they are similar to a very tightly coupled AC mains
transformer that is operated backwards. They are designed to the
specifications of the manufacturer and are not general purpose
devices.

If you mean DC-DC switching transformers then there are very many
different types depending on the needs of the circuit and the
parameters to be optimized.

Here is a short list of parameters that you might want to optimize
during design:
  o cost
  o efficiency
  o input supply voltage range (80V to 800V anyone)
  o short circuit current
  o operating temperature

When designing transformers it is common to work closly with the
company that will be producing the transformer for you. You call them
and tell them your requirements and they send you a sample to test.
You might take it apart and rewind it or tweak it a bit and then get
another sample until it just fits your requirements then you test the
heck out of it and maybe you specify it in your final design. This
works very well for high volume manufacturing solutions.

You can get off the shelf transformers that have six equal windings
and by connecting the windings in series or parallel you can get good
results for certain applications. This is the most generic approach I
have seen to switching transfomers.

There are many other types of transformers such as current
transformers, regulating tranformers, RF transformers etc.

--- In Electronics_101@yahoogroups.com, "MAG" <nereus@l...> wrote:
> On the subject of transformers.
> Does anyone know where I could find a matrix of the various types of
> transformers and their functions?
> I know of power transformers. But what about inverter transformers?
How many
> different kinds of  transformer are there?
>
> MAG

Hello vk6vhf28

On 05-Aug-03, you wrote:

> hi all
>         looking for a circuit diagram for my philips CD 960 cd
> player ! havebeen having problem with the cd draw for some time and
> now it wont open at all !would be pleased to hear from anyone who
> has any ideas
> regards ron
>
> ronb28@...

Hmmmm I wonder if we ever actually sold that model.  I'll take a look when I
get to work today for you ok? Check back here later :)




-----
Brian J Hoskins
South Wales, UK

Email: BrianJHoskins@...
Mobile: 07967 240380

Amiga 040/PPC, Amiga OS3.9.
-----

hi all
         looking for a circuit diagram for my philips CD 960 cd
player ! havebeen having problem with the cd draw for some time and
now it wont open at all !would be pleased to hear from anyone who
has any ideas
regards ron

ronb28@...



To unsubscribe from this group, send an email to:
Electronics_101-unsubscribe@yahoogroups.com



Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.

I was just playing around with my Wart/battery supply stuff and
discovered that the schottky diodes aren't acting as I expected.

With a 1N4148 reverse biased using 14VDC, I measure about 5 mV
coming out. With the 1N15818/5819, I measure the full 14 volts!
Granted, the current is down to 0.006mA but it still worries me. If
I apply 14V to a 9V or AA 4pack of alkalines, won't the 14V end up
destroying them after a while, even at 6uV?

If so, is there a little heftier low drop diode that I could use to
isolate batteries from wart power that has a low voltage drop?

My current project is now down to 13mA avg with bursts of 20mA so
the 1N4148 is plenty (70mA max), but I might get heftier things
going later.

I would also be interested in hearing more about specialty transformers --
structurally different transformers used for particular purposes.

But some of the "types"  we're talking about here are, as MAG suggested,
more about applications than actual physical differences in transformers.

    Power transformers are just transformers wound to step voltages  up or
down, sometimes with multiple taps to allow different output input and
output voltages. Of course, they also step current up and down
proportionally, so that the First Law of Thermodynamics doesn't get rudely
violated ;)

Output transformers and coupling transformers are used to match impedances
between devices or between segments of a circuit -- a very important
function, to be sure. The ratio of impedances is equal to the square of the
turns ratio, so that's what determines what kind of transformer is used in
this situation.

Transformers also provide isolation, obviously, since they can pass current
from a source to a circuit without an actual conducting connection.

I'm an audio person, so that's about all I use transformers for...I'm sure
there are many other applications...,

BTW, from an audio point of view, much has been made of the physical
characteristics of transformers as they pertain to sound reproduction. What
kind of core the transformer has, whether it was wound on a paper bobbin or
a plastic one, whether the windings are staggered or not, etc.  Some of
this is the stuff of lore, but it does seem to be true that frequency
response is affected by the arhcitecture and composition of the core.

Skip

Skip








At 04:08 AM 8/5/2003 +0000, you wrote:
>Hmm, that questions is a little like asking how many different kinds
>of circuits there are.
>
>If by inverter transformers you mean those that are used in
>Uniterruptable Power Systems (UPS) then there are a few different
>types but they are similar to a very tightly coupled AC mains
>transformer that is operated backwards. They are designed to the
>specifications of the manufacturer and are not general purpose
>devices.
>
>If you mean DC-DC switching transformers then there are very many
>different types depending on the needs of the circuit and the
>parameters to be optimized.
>
>Here is a short list of parameters that you might want to optimize
>during design:
>  o cost
>  o efficiency
>  o input supply voltage range (80V to 800V anyone)
>  o short circuit current
>  o operating temperature
>
>When designing transformers it is common to work closly with the
>company that will be producing the transformer for you. You call them
>and tell them your requirements and they send you a sample to test.
>You might take it apart and rewind it or tweak it a bit and then get
>another sample until it just fits your requirements then you test the
>heck out of it and maybe you specify it in your final design. This
>works very well for high volume manufacturing solutions.
>
>You can get off the shelf transformers that have six equal windings
>and by connecting the windings in series or parallel you can get good
>results for certain applications. This is the most generic approach I
>have seen to switching transfomers.
>
>There are many other types of transformers such as current
>transformers, regulating tranformers, RF transformers etc.
>
>--- In Electronics_101@yahoogroups.com, "MAG" <nereus@l...> wrote:
> > On the subject of transformers.
> > Does anyone know where I could find a matrix of the various types of
> > transformers and their functions?
> > I know of power transformers. But what about inverter transformers?
>How many
> > different kinds of  transformer are there?
> >
> > MAG
>
>
>
>To unsubscribe from this group, send an email to:
>Electronics_101-unsubscribe@yahoogroups.com
>
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

----- Original Message -----

From: Vijay Raju

To: Electronics_101@yahoogroups.com

Sent: 8/1/03 9:54:39 PM

Subject: RE: [Electronics_101] 230V AC as i/p to a uC

Hi,

 

Thanks! Initially I was trying to do the same thing trying to drop the voltage across a large resistor. But things were getting hot and ugly. The idea here is to use the reactance of the cap to drop the voltage. In fact I got this idea from a microchip app note (www.microchip.com/download/appnote/pic16/91008b.pdf)

 

I have a good amount of time about 500 ms to detect a change over. I just want to know how to get the time constant right.

 

 

Regards,

 

                     ,,,

                    (@-@)

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        {        Thoughts from        |

        {         Vijay  Raju         |

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                   ooO Ooo

 

-----Original Message-----
From: Scott Thompson [mailto:blueelectron9@...]
Sent: Friday, August 01, 2003 10:32 PM
To: Electronics_101@yahoogroups.com
Subject: RE: [Electronics_101] 230V AC as i/p to a uC

 

The 470uF capacitor is holding a lot of charge on the LED.  The optocoupler has what is called a current transfer ratio (CTR), so the LED is biased slightly on at all tiimes because of the charge of C17 and the output is reflecting the current fluctuation in the GaAs LED (U2).  Also, the 1N4001's are only rated at 50PIV and they may conduct during a portion of the cycle due to the charge of the 0.33uF capacitor.

 

You only need about 2V @ 10 mA to drive the LED.  At 230VAC, you have ~325V peak.  Take (325-2)/10 mA=R=33k.

 

Therefore, your circuit would like like this:

 

On JR2.1, replace the 100R 2W resistor with the 33k ohm resistor.  The resistor should be rated at about 5W.  You can use a 2W resistor since the input is always changing.  If you want to use lower power valued resistors, you can make a capacitive voltage divider first.  The problem with a capacitive voltage divider is that if bottom capacitor opens, you will be left with the full voltage anyway, so it's probably better to just be prepared to handle what may come down the pipe.

 

Kill the 1M resistor and C19.  Replace the diodes with 1N4004s or 1N4005s.  Kill the 470uF capacitor.

 

Place PD2 on an INPUT pin of the microcontroller instead of an OUTPUT pin.  You may damage your microcontroller if you are are forcing an output to change state.

 

Your circuit should now work properly.  Note that when the voltage on the line goes above about 1.7V, the output will go LOW (0V).  The output will swing high when the LED is not on (i.e., most of the AC cycle).  Therefore, expect to see a very narrow pulse from +5V to 0V around the rising zero-crossing level of the input voltage.

 

You may wish to include a zener or something in place of the first 1N4001 in case of a power surge.

 

For further information on interfacing to AC power lines (and a very simple one resistor approach), see Microchip's website and look at their application notes.  They rely on the maximum current into the microcontroller pin and the fact that there is intrinsic diodes to the power line rails to determine a value of resistance that will limit the input current to something that the microcontroller can handle.  All of the excess voltage just gets dumped across the very high valued resistor.

 

Personally, I'd stick with the optocoupler.

 

Good luck,

Scotty

 

----- Original Message -----

From: Vijay Raju

To: Electronics_101@yahoogroups.com

Sent: 8/1/03 7:04:25 AM

Subject: [Electronics_101] 230V AC as i/p to a uC

 

Hi,

 

         I am using the ckt in the attachment to detect 230V AC arriving on an output of an industrial PLC. I am trying to step down the voltage to 5V so my microcontroller can recognize the presence or absence of 230V. Now the problem is that the ckt seems to hold charge for really long times. i.e. if I remove the 230V input for a couple of minutes the output of the MCT2E is low. The second problem is that the output of the MCT2E is varying only between 4 and 5V. i.e 4V at 230V and 5V at 0V. What could be causing these problems?

 

 

Regards,  

 

                    ,,,

                    (@-@)

        +==---o00----(_)----00o-----==+

        {                             |

        {        Thoughts from        |

        {         Vijay  Raju         |

        {                             |

        +==-------------------------==+

                   |__|__|

                    || ||

                   ooO Ooo

 

 

 

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