Pin Protection
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I'm trying to design a idiot proof type system for 24vdc Logic use. Here is
what I have "so far". I'm a bigtime dummy on electronics so any suggestions
are most welcome.
I have 8 inputs, and 8 outputs.
Inputs:
Optos's , 24vdc running thru a 4.7k resistor to to opto led, single wire
interface (from the Opto Led) to the end devices (switches). When the
single wire is grounded, Opto Led is powered, thus sending a high to the
micros input pin. I "think" the most that can go wrong here is the
following: 1) A person could short out the input which shouldn't do
anything but turn on the opto. 2) A person could tie 24vdc + to the input
which shouldn't do anything but leave the opto in an off state. The Opto
would be wired like Jon's High_High Opto Schematic on the Yahoo files
section. I haven't selected an Opto yet, and don't know much about them.
Outputs:
Darlington UNL2803. A micros high output causes the Darlington to Sink it's
output to ground, activating relays or lamps. Relays and lamps are 24vdc
powered and as I mentioned, their grounds goto the darlington.
If someone ties a direct ground to the terminal, nothing should happen,
however if they tied 24 volts to the terminal, we have a direct short and
the Darlington goes up in magical smoke.
So, would it be wise to install a current limiting resistor between the
Darlingtons output and the terminal block, to limit the current to say 350
ma in case it was shorted, or the load was too high? this should still
allow relays and pilot lights to operate, but might save the Darlington in
case of mis-wiring? 68ohm limits it to 350 ma @ 24 volts right?
Last but not least, In case the micros pin direction is incorrect, during
power up
should I add a resistor between the micros output pin and the Darlington
Input?
and should I add a resistor between the Micros Input pin and the Opto?
Richard
what I have "so far". I'm a bigtime dummy on electronics so any suggestions
are most welcome.
I have 8 inputs, and 8 outputs.
Inputs:
Optos's , 24vdc running thru a 4.7k resistor to to opto led, single wire
interface (from the Opto Led) to the end devices (switches). When the
single wire is grounded, Opto Led is powered, thus sending a high to the
micros input pin. I "think" the most that can go wrong here is the
following: 1) A person could short out the input which shouldn't do
anything but turn on the opto. 2) A person could tie 24vdc + to the input
which shouldn't do anything but leave the opto in an off state. The Opto
would be wired like Jon's High_High Opto Schematic on the Yahoo files
section. I haven't selected an Opto yet, and don't know much about them.
Outputs:
Darlington UNL2803. A micros high output causes the Darlington to Sink it's
output to ground, activating relays or lamps. Relays and lamps are 24vdc
powered and as I mentioned, their grounds goto the darlington.
If someone ties a direct ground to the terminal, nothing should happen,
however if they tied 24 volts to the terminal, we have a direct short and
the Darlington goes up in magical smoke.
So, would it be wise to install a current limiting resistor between the
Darlingtons output and the terminal block, to limit the current to say 350
ma in case it was shorted, or the load was too high? this should still
allow relays and pilot lights to operate, but might save the Darlington in
case of mis-wiring? 68ohm limits it to 350 ma @ 24 volts right?
Last but not least, In case the micros pin direction is incorrect, during
power up
should I add a resistor between the micros output pin and the Darlington
Input?
and should I add a resistor between the Micros Input pin and the Opto?
Richard
Comments
> I'm trying to design a idiot proof type system for 24vdc Logic
use. Here is
> what I have "so far". I'm a bigtime dummy on electronics so any
suggestions
> are most welcome.
>
> I have 8 inputs, and 8 outputs.
>
> Inputs:
> Optos's , 24vdc running thru a 4.7k resistor to to opto led,
single wire
> interface (from the Opto Led) to the end devices (switches).
When the
> single wire is grounded, Opto Led is powered, thus sending a high
to the
> micros input pin. I "think" the most that can go wrong here is the
> following: 1) A person could short out the input which shouldn't
do
> anything but turn on the opto. 2) A person could tie 24vdc + to
the input
> which shouldn't do anything but leave the opto in an off state.
The Opto
> would be wired like Jon's High_High Opto Schematic on the Yahoo
files
> section. I haven't selected an Opto yet, and don't know much about
them.
>
The set-up I would use is a H11AA1 opto and two screw terminals and
not a common ground. IIRC, the chips is available in a 4 pin version
which I preferr but may be more common in a 6 pin package.
The idea of each input on screw terminals is that if you run a common
ground for all your inputs, you can wire up a short. on individual
terminals, you are fine.
The H11AA takes care of the reverse wiring problem with AC or DC.
>
> Outputs:
> Darlington UNL2803. A micros high output causes the Darlington to
Sink it's
> output to ground, activating relays or lamps. Relays and lamps are
24vdc
> powered and as I mentioned, their grounds goto the darlington.
> If someone ties a direct ground to the terminal, nothing should
happen,
> however if they tied 24 volts to the terminal, we have a direct
short and
> the Darlington goes up in magical smoke.
How does the saying go ? you can try to make things fool proof, but
fools can devise some very clever things ?
> So, would it be wise to install a current limiting resistor between
the
> Darlingtons output and the terminal block, to limit the current to
say 350
> ma in case it was shorted, or the load was too high? this should
still
> allow relays and pilot lights to operate, but might save the
Darlington in
> case of mis-wiring?
Here, I would considder a different approach. a diode would prevent
this problem and not have to live with the heat of the current thru
the device.
> 68ohm limits it to 350 ma @ 24 volts right?
>
> Last but not least, In case the micros pin direction is incorrect,
during
> power up
> should I add a resistor between the micros output pin and the
Darlington
> Input?
> and should I add a resistor between the Micros Input pin and the
Opto?
Are you saying that someone might put the Stamp in BACKWARDS ? Now,
I think you are over designing. besides, you don't allow for broken
pins on the chip..... : )
The input from the opto is 5V, board voltage and does not need to be
isolated in the layout, but you can certainly put in a 1k resistor if
you like.
the output to the darlington should have a resistor in the line,
again, 1k would be fine.
Thinking about a reverse installed chip, the logic side of the Stamp
would be connnected to all low current inputs with 1k resistors
installed.
the pins 1-4 and 20-24 would be the ones in question. pins 1-4 are
no problem so that really leaves pins 22 and 24. For this, I would
expect 5V regulated on pin 22. Check me if I'm wrong, but just
applying 5 volts to an input/output pin will not damage it.
Since I like to add features, I'd considder adding LED's on the
opto's to show the input state. no light, no signal.
ditto for the darlington, but here, I'd put it on the BS2 side to
indicate if you have a signal out.
Dave
>
> Richard
to Powering up and the inputs and outputs not being set correctly in the
begiining.
Original Message
From: "Dave Mucha" <davemucha@j...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, June 10, 2004 11:33 AM
Subject: [noparse][[/noparse]basicstamps] Re: Pin Protection
> --- In basicstamps@yahoogroups.com, "Richard" <rwskinner@a...> wrote:
> > I'm trying to design a idiot proof type system for 24vdc Logic
> use. Here is
> > what I have "so far". I'm a bigtime dummy on electronics so any
> suggestions
> > are most welcome.
> >
> > I have 8 inputs, and 8 outputs.
> >
> > Inputs:
> > Optos's , 24vdc running thru a 4.7k resistor to to opto led,
> single wire
> > interface (from the Opto Led) to the end devices (switches).
> When the
> > single wire is grounded, Opto Led is powered, thus sending a high
> to the
> > micros input pin. I "think" the most that can go wrong here is the
> > following: 1) A person could short out the input which shouldn't
> do
> > anything but turn on the opto. 2) A person could tie 24vdc + to
> the input
> > which shouldn't do anything but leave the opto in an off state.
> The Opto
> > would be wired like Jon's High_High Opto Schematic on the Yahoo
> files
> > section. I haven't selected an Opto yet, and don't know much about
> them.
> >
>
>
> The set-up I would use is a H11AA1 opto and two screw terminals and
> not a common ground. IIRC, the chips is available in a 4 pin version
> which I preferr but may be more common in a 6 pin package.
>
> The idea of each input on screw terminals is that if you run a common
> ground for all your inputs, you can wire up a short. on individual
> terminals, you are fine.
>
> The H11AA takes care of the reverse wiring problem with AC or DC.
>
>
> >
> > Outputs:
> > Darlington UNL2803. A micros high output causes the Darlington to
> Sink it's
> > output to ground, activating relays or lamps. Relays and lamps are
> 24vdc
> > powered and as I mentioned, their grounds goto the darlington.
> > If someone ties a direct ground to the terminal, nothing should
> happen,
> > however if they tied 24 volts to the terminal, we have a direct
> short and
> > the Darlington goes up in magical smoke.
>
> How does the saying go ? you can try to make things fool proof, but
> fools can devise some very clever things ?
>
>
> > So, would it be wise to install a current limiting resistor between
> the
> > Darlingtons output and the terminal block, to limit the current to
> say 350
> > ma in case it was shorted, or the load was too high? this should
> still
> > allow relays and pilot lights to operate, but might save the
> Darlington in
> > case of mis-wiring?
>
>
> Here, I would considder a different approach. a diode would prevent
> this problem and not have to live with the heat of the current thru
> the device.
>
> > 68ohm limits it to 350 ma @ 24 volts right?
> >
> > Last but not least, In case the micros pin direction is incorrect,
> during
> > power up
> > should I add a resistor between the micros output pin and the
> Darlington
> > Input?
> > and should I add a resistor between the Micros Input pin and the
> Opto?
>
>
> Are you saying that someone might put the Stamp in BACKWARDS ? Now,
> I think you are over designing. besides, you don't allow for broken
> pins on the chip..... : )
>
>
> The input from the opto is 5V, board voltage and does not need to be
> isolated in the layout, but you can certainly put in a 1k resistor if
> you like.
>
> the output to the darlington should have a resistor in the line,
> again, 1k would be fine.
>
>
> Thinking about a reverse installed chip, the logic side of the Stamp
> would be connnected to all low current inputs with 1k resistors
> installed.
>
> the pins 1-4 and 20-24 would be the ones in question. pins 1-4 are
> no problem so that really leaves pins 22 and 24. For this, I would
> expect 5V regulated on pin 22. Check me if I'm wrong, but just
> applying 5 volts to an input/output pin will not damage it.
>
> Since I like to add features, I'd considder adding LED's on the
> opto's to show the input state. no light, no signal.
>
> ditto for the darlington, but here, I'd put it on the BS2 side to
> indicate if you have a signal out.
>
>
> Dave
>
>
>
> >
> > Richard
>
>
>
> To UNSUBSCRIBE, just send mail to:
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>
>
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>
<rwskinner@a...> wrote:
> Well, I wasn't referring to installing the stamp backwards. I was
referring
> to Powering up and the inputs and outputs not being set correctly
in the
> begining.
That is not a worry at all.
The inputs will have no effect.
the outputs may but that is more of a problem of if you have your
sunglasses on, when it turns on a light unexpectdly.
Dave
What size traces are good for using on the UNL2803? I used .100 from the
2803 to ground, as well as .100 from the 2803 back the 24vdc. The Logic
traces are .015" and the traces from the terminal blocks to the collectors
are 0.025". (these are the ones that will sink back to ground for each
individual output).
Double Check Wiring:
I tied the 2803 Ground Terminal 9 to 5vdc Logic Ground, and to the 24 vdc
External power Ground. I ran terminal #10 from the 2803 (Fly back diodes)
back to the 24 vdc External Positive.
For Output Active Indicator, I put a LED on each output. The LED ties to
24+ then the other side goes thru a 4.7k resistor and ties to the output of
the 2803. I have these on all 8 outputs. ??? 24 / 4700 = 5ma. Is that
enough for LED's?
1K Resistor installed between each 2803 and the Digital Output. (Sorry,
what is it in there for?)
I see the 2803 already has 2.7k resistors between the input terminals and
the base. The specs show the 2803A only requiring an input current of
roughly 1 ma @ 5vdc.
> Here, I would considder a different approach. a diode would prevent
> this problem and not have to live with the heat of the current thru
> the device.
>
Any particular type of diode to use for reverse polarity protection on the
2803 outputs?
Just install it in Series on each output, bar going towards the screw
terminal?
Thanks Again,
Richard
Original Message
From: "Dave Mucha" <davemucha@j...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, June 10, 2004 11:33 AM
Subject: [noparse][[/noparse]basicstamps] Re: Pin Protection
> --- In basicstamps@yahoogroups.com, "Richard" <rwskinner@a...> wrote:
> > I'm trying to design a idiot proof type system for 24vdc Logic
> use. Here is
> > what I have "so far". I'm a bigtime dummy on electronics so any
> suggestions
> > are most welcome.
> >
> > I have 8 inputs, and 8 outputs.
> >
> > Inputs:
> > Optos's , 24vdc running thru a 4.7k resistor to to opto led,
> single wire
> > interface (from the Opto Led) to the end devices (switches).
> When the
> > single wire is grounded, Opto Led is powered, thus sending a high
> to the
> > micros input pin. I "think" the most that can go wrong here is the
> > following: 1) A person could short out the input which shouldn't
> do
> > anything but turn on the opto. 2) A person could tie 24vdc + to
> the input
> > which shouldn't do anything but leave the opto in an off state.
> The Opto
> > would be wired like Jon's High_High Opto Schematic on the Yahoo
> files
> > section. I haven't selected an Opto yet, and don't know much about
> them.
> >
>
>
> The set-up I would use is a H11AA1 opto and two screw terminals and
> not a common ground. IIRC, the chips is available in a 4 pin version
> which I preferr but may be more common in a 6 pin package.
>
> The idea of each input on screw terminals is that if you run a common
> ground for all your inputs, you can wire up a short. on individual
> terminals, you are fine.
>
> The H11AA takes care of the reverse wiring problem with AC or DC.
>
>
> >
> > Outputs:
> > Darlington UNL2803. A micros high output causes the Darlington to
> Sink it's
> > output to ground, activating relays or lamps. Relays and lamps are
> 24vdc
> > powered and as I mentioned, their grounds goto the darlington.
> > If someone ties a direct ground to the terminal, nothing should
> happen,
> > however if they tied 24 volts to the terminal, we have a direct
> short and
> > the Darlington goes up in magical smoke.
>
> How does the saying go ? you can try to make things fool proof, but
> fools can devise some very clever things ?
>
>
> > So, would it be wise to install a current limiting resistor between
> the
> > Darlingtons output and the terminal block, to limit the current to
> say 350
> > ma in case it was shorted, or the load was too high? this should
> still
> > allow relays and pilot lights to operate, but might save the
> Darlington in
> > case of mis-wiring?
>
>
> Here, I would considder a different approach. a diode would prevent
> this problem and not have to live with the heat of the current thru
> the device.
>
> > 68ohm limits it to 350 ma @ 24 volts right?
> >
> > Last but not least, In case the micros pin direction is incorrect,
> during
> > power up
> > should I add a resistor between the micros output pin and the
> Darlington
> > Input?
> > and should I add a resistor between the Micros Input pin and the
> Opto?
>
>
> Are you saying that someone might put the Stamp in BACKWARDS ? Now,
> I think you are over designing. besides, you don't allow for broken
> pins on the chip..... : )
>
>
> The input from the opto is 5V, board voltage and does not need to be
> isolated in the layout, but you can certainly put in a 1k resistor if
> you like.
>
> the output to the darlington should have a resistor in the line,
> again, 1k would be fine.
>
>
> Thinking about a reverse installed chip, the logic side of the Stamp
> would be connnected to all low current inputs with 1k resistors
> installed.
>
> the pins 1-4 and 20-24 would be the ones in question. pins 1-4 are
> no problem so that really leaves pins 22 and 24. For this, I would
> expect 5V regulated on pin 22. Check me if I'm wrong, but just
> applying 5 volts to an input/output pin will not damage it.
>
> Since I like to add features, I'd considder adding LED's on the
> opto's to show the input state. no light, no signal.
>
> ditto for the darlington, but here, I'd put it on the BS2 side to
> indicate if you have a signal out.
>
>
> Dave
>
>
>
> >
> > Richard
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
> Yahoo! Groups Links
>
>
>
>
>
>
> [noparse][[/noparse]Scanned by AwesomeNet Anti-Virus]
>
>
<rwskinner@a...> wrote:
> Trace Size:
> What size traces are good for using on the UNL2803? I used .100
from the
> 2803 to ground, as well as .100 from the 2803 back the 24vdc. The
Logic
> traces are .015" and the traces from the terminal blocks to the
collectors
> are 0.025". (these are the ones that will sink back to ground for
each
> individual output).
1 ounce copper, 100 mil wide = 5 amps. more than enough.
30 mil trace = 2 amps
<snip>
>
> For Output Active Indicator, I put a LED on each output. The LED
ties to
> 24+ then the other side goes thru a 4.7k resistor and ties to the
output of
> the 2803. I have these on all 8 outputs. ??? 24 / 4700 = 5ma.
Is that
> enough for LED's?
A lot of people use 10mA for an LED, but 5 will make it light. It's
one of the more simple things to test before you do all 8.
>
> 1K Resistor installed between each 2803 and the Digital Output.
(Sorry,
> what is it in there for?)
> I see the 2803 already has 2.7k resistors between the input
terminals and
> the base. The specs show the 2803A only requiring an input current
of
> roughly 1 ma @ 5vdc.
2803 = $39 cents
1k resistor = 3 cents
peace of mind if the 2803 smokes ? PRICELESS !
<snip>
> Any particular type of diode to use for reverse polarity protection
on the 2803 outputs?
> Just install it in Series on each output, bar going towards the
screw terminal?
Since you are talking as fool proof as possible, you can put on two
screw terminals and use 4 diodes per pair of terminals.
Each terminal would would connect from the terminal thru a doide and
to the input of the 2803.
And the ground would connect thru a diode to each terminal. That
way, there is no wrong way to connect a pair of wires.
1N4001 is fine, there will be a slight voltage drop per diode, but
your main concern is the voltage rating of the diode.
I'd be interested if anybody else has any ideas on how to design for
incorrect polarity on inputs.
Dave
Original Message
From: "Dave Mucha" <davemucha@j...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, June 10, 2004 8:22 PM
Subject: [noparse][[/noparse]basicstamps] Re: Pin Protection
> --- In basicstamps@yahoogroups.com, "Richard Skinner"
> <rwskinner@a...> wrote:
> > Trace Size:
> > What size traces are good for using on the UNL2803? I used .100
> from the
> > 2803 to ground, as well as .100 from the 2803 back the 24vdc. The
> Logic
> > traces are .015" and the traces from the terminal blocks to the
> collectors
> > are 0.025". (these are the ones that will sink back to ground for
> each
> > individual output).
>
> 1 ounce copper, 100 mil wide = 5 amps. more than enough.
> 30 mil trace = 2 amps
>
> <snip>
> >
> > For Output Active Indicator, I put a LED on each output. The LED
> ties to
> > 24+ then the other side goes thru a 4.7k resistor and ties to the
> output of
> > the 2803. I have these on all 8 outputs. ??? 24 / 4700 = 5ma.
> Is that
> > enough for LED's?
>
> A lot of people use 10mA for an LED, but 5 will make it light. It's
> one of the more simple things to test before you do all 8.
>
>
> >
> > 1K Resistor installed between each 2803 and the Digital Output.
> (Sorry,
> > what is it in there for?)
> > I see the 2803 already has 2.7k resistors between the input
> terminals and
> > the base. The specs show the 2803A only requiring an input current
> of
> > roughly 1 ma @ 5vdc.
>
> 2803 = $39 cents
> 1k resistor = 3 cents
> peace of mind if the 2803 smokes ? PRICELESS !
>
> <snip>
>
> > Any particular type of diode to use for reverse polarity protection
> on the 2803 outputs?
> > Just install it in Series on each output, bar going towards the
> screw terminal?
>
> Since you are talking as fool proof as possible, you can put on two
> screw terminals and use 4 diodes per pair of terminals.
>
> Each terminal would would connect from the terminal thru a doide and
> to the input of the 2803.
>
> And the ground would connect thru a diode to each terminal. That
> way, there is no wrong way to connect a pair of wires.
>
> 1N4001 is fine, there will be a slight voltage drop per diode, but
> your main concern is the voltage rating of the diode.
>
> I'd be interested if anybody else has any ideas on how to design for
> incorrect polarity on inputs.
>
> Dave
>
>
>
>
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
> Yahoo! Groups Links
>
>
>
>
>
>
> [noparse][[/noparse]Scanned by AwesomeNet Anti-Virus]
>
>