| Author |
Message |
w_tom
Guest
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 Posted:
Tue Feb 15, 2005 5:43 am Post subject:
Re: Help with Telephone Circuit |
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Some of the usual suspects not seen in responses. Do you
have a bypass capacitor adjacent to the 74HC123? Bypass cap
is more critical with the HC version compared to the LS
version. And it must make a short connection to that 74HC123
chip. Schematic does not show it.
You did connect power and ground to pins 16 and 8. HC chips
can be powered, unstable, via other pins if the Vcc and Gnd
pins are not connected.
Another has recommended the relay be grounded separate from
HC ground. Remember, wire is an electronic component and not
a perfect conductor.
Many responses assume the phone line is electrically
isolated from the rest of that circuit. Maybe. But then
separation between phone line components and wires is
important for proper operation.
You are suffering a transient problem. But too many post as
if a transient enters on one wire, causes the problem, and
terminates. View transient problems in terms of both incoming
and outgoing path. For example, the transient may enter on
one AC power wire and leave on the other. Or it may enter on
one AC wire and leave via a not so well separated wire to
phone line.
Remember, there is no complete isolation between relay wiper
and relay solenoid. We have seen where a transient on the HC
output will actually trigger that IC to change state.
An oscilloscope using two probes (in differential mode)
would go a long way to finding the problem in but minutes.
Currently we all can only speculate. Provides above are some
examples of the usual suspects.
Trudeau wrote:
| Quote: | Thanks again for your advice.
Actually, and again because I'm learning the the >(12-9v) may have been
miss leading. I copied it from the little diagram that I had in how to use
the 7805 and it meant to me anyway that I could start with anything from 9
to 12 volts. and the regulator would bring it down to 5 volts. I know that
you could actually start with a higher input voltage but for us home bodies
who has a 30v AC/DC adaptor. Most everything is 12 or under. (my experience
anyway) I have not or don't recall anyway actually checking the voltage on
the AC/DC adaptor accept what its rated for which is 9Volts.
Again thank you for the advice I must now think it through. I have not seen
a 78L05 but looked it up and sure enough there it is. It does look like a
better regulator. Or at least more suitable for this application. I can't
imagine anything I would do that would actually need 5v, 1 amp that can come
from the 7805.
Thanks again I will digest it all. |
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Trudeau
Guest
|
| Posted:
Tue Feb 15, 2005 10:26 pm Post subject:
Re: Help with Telephone Circuit |
|
|
"w_tom" <w_tom1@hotmail.com> wrote in message
news:42113799.920DDF2D@hotmail.com...
| Quote: | Some of the usual suspects not seen in responses. Do you
have a bypass capacitor adjacent to the 74HC123? Bypass cap
is more critical with the HC version compared to the LS
version. And it must make a short connection to that 74HC123
chip. Schematic does not show it.
You did connect power and ground to pins 16 and 8. HC chips
can be powered, unstable, via other pins if the Vcc and Gnd
pins are not connected.
Another has recommended the relay be grounded separate from
HC ground. Remember, wire is an electronic component and not
a perfect conductor.
Many responses assume the phone line is electrically
isolated from the rest of that circuit. Maybe. But then
separation between phone line components and wires is
important for proper operation.
You are suffering a transient problem. But too many post as
if a transient enters on one wire, causes the problem, and
terminates. View transient problems in terms of both incoming
and outgoing path. For example, the transient may enter on
one AC power wire and leave on the other. Or it may enter on
one AC wire and leave via a not so well separated wire to
phone line.
Remember, there is no complete isolation between relay wiper
and relay solenoid. We have seen where a transient on the HC
output will actually trigger that IC to change state.
An oscilloscope using two probes (in differential mode)
would go a long way to finding the problem in but minutes.
Currently we all can only speculate. Provides above are some
examples of the usual suspects.
Trudeau wrote:
Thanks again for your advice.
Actually, and again because I'm learning the the >(12-9v) may have been
miss leading. I copied it from the little diagram that I had in how to
use
the 7805 and it meant to me anyway that I could start with anything from
9
to 12 volts. and the regulator would bring it down to 5 volts. I know
that
you could actually start with a higher input voltage but for us home
bodies
who has a 30v AC/DC adaptor. Most everything is 12 or under. (my
experience
anyway) I have not or don't recall anyway actually checking the voltage
on
the AC/DC adaptor accept what its rated for which is 9Volts.
Again thank you for the advice I must now think it through. I have not
seen
a 78L05 but looked it up and sure enough there it is. It does look like
a
better regulator. Or at least more suitable for this application. I
can't
imagine anything I would do that would actually need 5v, 1 amp that can
come
from the 7805.
Thanks again I will digest it all.
|
Thanks for you tips. I keep adding data to my knowledge.
The idea of grounding the relay etc is an interesting one suggested by you
and another poster. Im a little unclear on this exactly. I would not have
thought that on such a little circuit it would be much resistance. If I
understand what people are saying I asume what people really mean there
should be a separate negative - connection put closer to the emitter side of
the T1 close to it to prevent the electricity traveling as far to the relay.
And absorb some of the voltage fluctionations. If you put it on the
collector side it would trip the relay. And not work properly. If people
mean someone else I would apreaciate knowing.
Another respectable answer was to "separately" power the + side of the relay
of a sort.
see "John Fields February 14, 2005 1:42 PM" in this thread for details. I
would have never thought of that and find it a facinating way of doing it.
Its a lively news group with some thoughtfull answers.
Regards |
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w_tom
Guest
|
| Posted:
Tue Feb 15, 2005 10:47 pm Post subject:
Re: Help with Telephone Circuit |
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|
In electronics, noise on the ground pin will cause more
noise problems as compared to noise on the Vcc line or other
IC pins. Therefore we may create separate digital ground,
analog ground, and periperhal driver ground that only join at
one point. This longer distance in copper between the
different family of components creates reactive electronic
components - the copper traces - to separate the different
grounds.
In your case, digital electronic ground and the relay
peripheral ground would be separate until both meet where a
power supply ground connects. Copper traces are more
electronic components. Resistance is not the problem. Copper
impedance is the reason we do these things. This electronic
nature of copper is also why the bypass capacitor (typically
ceramic) must be located adjacent to the 74HC123.
Trudeau wrote:
| Quote: | Thanks for you tips. I keep adding data to my knowledge.
The idea of grounding the relay etc is an interesting one suggested
by you and another poster. Im a little unclear on this exactly. I
would not have thought that on such a little circuit it would be
much resistance. If I understand what people are saying I asume
what people really mean there should be a separate negative -
connection put closer to the emitter side of the T1 close to it to
prevent the electricity traveling as far to the relay. And absorb
some of the voltage fluctionations. If you put it on the collector
side it would trip the relay. And not work properly. If people
mean someone else I would apreaciate knowing. Another respectable
answer was to "separately" power the + side of the relay of a sort.
see "John Fields February 14, 2005 1:42 PM" in this thread for
details. I would have never thought of that and find it a
facinating way of doing it.
Its a lively news group with some thoughtfull answers.
Regards |
|
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| Back to top |
|
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ryan wiehle
Guest
|
| Posted:
Wed Feb 16, 2005 2:11 am Post subject:
Re: Help with Telephone Circuit |
|
|
Trudeau wrote:
| Quote: | I have build the following project.
http://electronicsworld.tripod.com/telephonesimages/12.gif
The circuit works for the most part.
There is one problem however that I have.
The problem seems to show its self in two different ways.
1. The light turns on at erratic times, eg when the furnace turns
off. Not all the time but every once and a while I hear the forced
air fan of the furnace turn off and click the relay in the smart
light turns on and the light turns on. I'm sure the furnace is on a
separate circuit.
2. When someone calls in at the end of the first ring when there is
darkness the light turns on. Fine exactly what I want. However
sometimes the light keeps clicking on, remaining on for as long at
the capacitor allows, clicks off and then clicks back on then remains
on for as long as the capacitor allows etc. several times. Some times
its 3 times sometimes up to 10 times. It's what I call a bounce. The
light turns off, you hear the relay click OFF and then it seems to
bounces back ON and remains on for its scheduled time.
The relay is a 5 vdc relay with the right voltage rating to switch
120 Volts AC. I have it connected to a outlet in a box that I plug
the 40 watt lamp into.
I assume the problem is that some how the a 120VAC surge in power eg
the furnace and the lamp turning off is tripping the relay. The tell
tail sign of this is that if I pull the plug from the lamp that is
plugged into the "triggered" outlet and sort of push the plug in and
out a few times I can make the relay "CLICK" and it keeps the light
on for the scheduled time limit. In other words when I make my own
"Power Surge" it trips the circuit.
It seems odd to me because, the 120 volts is suppose to be completely
separate from the phone circuit. How can the 120 volts AC cause the
relay to "bounce" as described. And more to the point how do I
prevent it?
I hope Ive made it relatively clear on what my problem is.
Do you think it is simply the relay, is perhaps a bad choice or even
could a different Diode than the 1N4007 that is used over the relay
be used to solve the problem??
Thank you.
|
looked at your schematic. I suggest you replace the opto-coupler
with a schmitt-triger type opto-coupler to avoid
multiply spikes during the ring-cycle. |
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peterken
Guest
|
| Posted:
Wed Feb 16, 2005 6:10 am Post subject:
Re: Help with Telephone Circuit |
|
|
"ryan wiehle" <rw@rogers.com> wrote in message
news:8uqdnZLcYc_8yo_fRVn-pw@rogers.com...
| Quote: | Trudeau wrote:
I have build the following project.
http://electronicsworld.tripod.com/telephonesimages/12.gif
The circuit works for the most part.
There is one problem however that I have.
The problem seems to show its self in two different ways.
1. The light turns on at erratic times, eg when the furnace turns
off. Not all the time but every once and a while I hear the forced
air fan of the furnace turn off and click the relay in the smart
light turns on and the light turns on. I'm sure the furnace is on a
separate circuit.
2. When someone calls in at the end of the first ring when there is
darkness the light turns on. Fine exactly what I want. However
sometimes the light keeps clicking on, remaining on for as long at
the capacitor allows, clicks off and then clicks back on then remains
on for as long as the capacitor allows etc. several times. Some times
its 3 times sometimes up to 10 times. It's what I call a bounce. The
light turns off, you hear the relay click OFF and then it seems to
bounces back ON and remains on for its scheduled time.
The relay is a 5 vdc relay with the right voltage rating to switch
120 Volts AC. I have it connected to a outlet in a box that I plug
the 40 watt lamp into.
I assume the problem is that some how the a 120VAC surge in power eg
the furnace and the lamp turning off is tripping the relay. The tell
tail sign of this is that if I pull the plug from the lamp that is
plugged into the "triggered" outlet and sort of push the plug in and
out a few times I can make the relay "CLICK" and it keeps the light
on for the scheduled time limit. In other words when I make my own
"Power Surge" it trips the circuit.
It seems odd to me because, the 120 volts is suppose to be completely
separate from the phone circuit. How can the 120 volts AC cause the
relay to "bounce" as described. And more to the point how do I
prevent it?
I hope Ive made it relatively clear on what my problem is.
Do you think it is simply the relay, is perhaps a bad choice or even
could a different Diode than the 1N4007 that is used over the relay
be used to solve the problem??
Thank you.
looked at your schematic. I suggest you replace the opto-coupler
with a schmitt-triger type opto-coupler to avoid
multiply spikes during the ring-cycle.
|
Since ringtone is about 60Vac there'a always multiple triggering during the
rincycle...
Replacing the opto with a schmitt trigger type would only be helpfull if a
slow changing dc voltage would be applied at the 'ring' line |
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