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Hello Everyone,
I am new to the group and know just enough about electronics to be
dangerous. The circuit that I am trying to complete is 9V DC. I have
placed a phototransistor just before a relay. The relay is 5V. A
piezo alarm is connected to the "Normally Open" lead on the relay.
For some reason, I cannot get enough power through the
phototransistor to activated the relay switch. When I test the
circuit, the alarm quietly sounds and becomes slightly louder when
more light is applied.
It is as though there is resistance with regards to the
phototransistor.
Please forgive me is my terminology is incorrect. I hope that someone
understands this. Any help would be greatly appreciated.
Sincerely,
Kenyon Jones
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Yes
and no.
?
I
didn't quite catch how your circuit is build. A phototransistor does have
"variabel resistance". The more light you apply, the more Ic you get (light here
is used as the base current).
?
However, if you have the phototransistor turning on/off
a relay. And you have a piezo on the other side of the realy, the this resitance
shoulder matter. Cause the relay can only be on or off, nothing in
between.
?
Did I
misunderstand you here?
?
Mounir
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Hello
Everyone,
I am new to the group and know just enough about electronics
to be
dangerous. The circuit that I am trying to complete is 9V DC. I have
placed a phototransistor just before a relay. The relay is 5V. A
piezo
alarm is connected to the "Normally Open" lead on the relay.
For some
reason, I cannot get enough power through the
phototransistor to activated
the relay switch. When I test the
circuit, the alarm quietly sounds and
becomes slightly louder when
more light is applied.
It is as though
there is resistance with regards to the
phototransistor.
Please
forgive me is my terminology is incorrect. I hope that someone
understands
this. Any help would be greatly appreciated.
Sincerely,
Kenyon
Jones
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Hi there, your issue is probably that you don't get enough current
flowing throug the relay to operate it. All depends of course on the
characteristics of your relay. My suggestion would be to put another
transistor between the phototransistor and the relay to "enhance" the
switching power.
Br,
Leo
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-----Original Message-----
From: kenyonjones@m... [mailto:kenyonjones@m...]
Sent: Friday, October 26, 2001 12:19 PM
To: Electronics_101@y...
Subject: [Electronics_101] Light Activated Alarm
Hello Everyone,
I am new to the group and know just enough about electronics to be
dangerous. The circuit that I am trying to complete is 9V DC. I have placed a phototransistor just before a relay. The relay is 5V. A
piezo alarm is connected to the "Normally Open" lead on the relay.
For some reason, I cannot get enough power through the
phototransistor to activated the relay switch. When I test the
circuit, the alarm quietly sounds and becomes slightly louder when
more light is applied.
It is as though there is resistance with regards to the
phototransistor.
Please forgive me is my terminology is incorrect. I hope that someone understands this. Any help would be greatly appreciated.
Sincerely,
Kenyon Jones
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Mounir,
However,
if you have the phototransistor turning on/off a relay. And you have a
piezo on the other side of the realy, the this resitance shoulder matter.
Cause the relay can only be on or off, nothing in between.
Yes, but it the photo transistor is not conducting enough to operate the
relay or it's on the raged edge of conduction it might not work as well
as it should. I would try dumping the relay and putting the alarm device
in series with the collector and Vcc.
Jim
|
Kenyon,
Thank
you for your response. It seems that the photo transistor is conducting
enough to send minimal current through the relay but not enough to activate
the switch, so to speak.
In this case
you will probably require a second transistor, connect the phot transistor
with the collector at Vcc and the emitter on the base of the second transistor.
This way the first tranny provides bias to the second. Put the relay in
series with the second transistors collector and Vcc.
The emitter
can go to ground, i.e. p.s. comnon. These would both be NPN transistors
else you can turn the power supply upside down, i.e. pos. grounded etc.
My problem is
that I need the circuit to be such that the alarm continues, even if light
is removed from the photo transistor.
This will require
a latching device. If you are using a ralay instead of a solid state device
you can use an auxilliary set of contacts to hold the relay in after the
lighe 'goes away'. Or you could possibly use an SCR (silocon control rectifier)
in place of the second transistor, these devices stay on once triggered.
Could you tell
me more about "putting the alarm device in series with the collector and
VCC.
This is pretty strait foreward.? Connect one end of the relay to Vcc
(p.s. +)
and the other end of the relay to the transistor collector. The emitter
goes to ground, or p.s. common.? The base of a photo transistor goes
to light, i.e. the light turns on the transistor.? Or if this is the
second transistor it would be connected to the emitter of the first one.?
What I have described here is a very simplified description. More specifics
would depend on the nature of the devices used, etc.
Jim
|
Hey ,
?
put a 555 circuit in front of it in monostable mode
that will give a desired time for the switch to be on.... or if you want it to
be continuous then use it in bistable mode...(reffer the
data-sheets..)
?
Regards :-),
?
--himanshu sharma
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Show quoted text
----- Original Message -----
Sent: Tuesday, October 30, 2001 12:39
AM
Subject: RE: [Electronics_101] Light
Activated Alarm
Jim,
?
Thank you for your response. It seems that the photo
transistor is conducting enough to send minimal current through the relay but
not enough to activate the switch, so to speak. My problem is that I need the
circuit to be such that the alarm continues, even if light is removed from the
photo transistor. Could you tell me more about "putting the alarm device in
series with the collector and VCC. Again, I appreciate your
help.
?
Sincerely,
?
Kenyon Jones
?
Mounir,
However, if you have the phototransistor turning on/off a relay.
And you have a piezo on the other side of the realy, the this resitance
shoulder matter. Cause the relay can only be on or off, nothing in
between. Yes, but it the photo transistor
is not conducting enough to operate the relay or it's on the raged edge of
conduction it might not work as well as it should. I would try dumping the
relay and putting the alarm device in series with the collector and Vcc.
Jim
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Jim,
?
Thank
you for your response. It seems that the photo transistor is conducting enough
to send minimal current through the relay but not enough to activate the switch,
so to speak. My problem is that I need the circuit to be such that the alarm
continues, even if light is removed from the photo transistor. Could you tell me
more about "putting the alarm device in series with the collector and VCC.
Again, I appreciate your help.
?
Sincerely,
?
Kenyon
Jones
?
toggle quoted message
Show quoted text
Mounir,
However, if you have the phototransistor turning on/off a relay. And
you have a piezo on the other side of the realy, the this resitance shoulder
matter. Cause the relay can only be on or off, nothing in
between. Yes, but it the photo transistor is
not conducting enough to operate the relay or it's on the raged edge of
conduction it might not work as well as it should. I would try dumping the
relay and putting the alarm device in series with the collector and Vcc.
Jim
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to:
Electronics_101-unsubscribe@...
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Jim,
?
I am
very greatful and appreciate you taking the time to formulate this response. Not
being an electronics expert, your detail has helped me to understand what needs
to be done. Incidently, I am an investigator in the transportation industry and
this alarm will be placed inside of packages. If someone attempts to pilfer the
"test" package, the alarm will sound.
?
Again,
much thanks to you.
?
Sincerely,
?
Kenyon
Jones
?
?
?
toggle quoted message
Show quoted text
Kenyon,
Thank you for your response. It seems that the photo transistor is
conducting enough to send minimal current through the relay but not enough
to activate the switch, so to speak.
In this case you will
probably require a second transistor, connect the phot transistor with the
collector at Vcc and the emitter on the base of the second transistor. This
way the first tranny provides bias to the second. Put the relay in series
with the second transistors collector and Vcc.
The emitter can go to
ground, i.e. p.s. comnon. These would both be NPN transistors else you can
turn the power supply upside down, i.e. pos. grounded
etc.
My problem is that I
need the circuit to be such that the alarm continues, even if light is
removed from the photo transistor.
This will require a
latching device. If you are using a ralay instead of a solid state device
you can use an auxilliary set of contacts to hold the relay in after the
lighe 'goes away'. Or you could possibly use an SCR (silocon control
rectifier) in place of the second transistor, these devices stay on once
triggered.
Could you tell me more
about "putting the alarm device in series with the collector and
VCC. This is pretty strait
foreward.? Connect one end of the relay to Vcc (p.s. +)
and the other
end of the relay to the transistor collector. The emitter goes to ground, or
p.s. common.? The base of a photo transistor goes to light, i.e. the
light turns on the transistor.? Or if this is the second transistor it
would be connected to the emitter of the first one.? What I have
described here is a very simplified description. More specifics would depend
on the nature of the devices used, etc.
Jim
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to:
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|
----- Original Message -----
Sent: Tuesday, October 30, 2001 1:32
AM
Subject: Re: [Electronics_101] Light
Activated Alarm
Hey ,
?
put a 555 circuit in front of it in monostable
mode that will give a desired time for the switch to be on....
?
LOL.... this reminds me of time-bomb
!
?
?
--himanshu sharma
----- Original Message -----
Sent: Tuesday, October 30, 2001 12:39
AM
Subject: RE: [Electronics_101] Light
Activated Alarm
Jim,
?
Thank you for your response. It seems that the
photo transistor is conducting enough to send minimal current through the
relay but not enough to activate the switch, so to speak. My problem is that
I need the circuit to be such that the alarm continues, even if light is
removed from the photo transistor. Could you tell me more about "putting the
alarm device in series with the collector and VCC. Again, I appreciate your
help.
?
Sincerely,
?
Kenyon Jones
?
Mounir,
However, if you have the phototransistor turning on/off a relay.
And you have a piezo on the other side of the realy, the this resitance
shoulder matter. Cause the relay can only be on or off, nothing in
between. Yes, but it the photo transistor
is not conducting enough to operate the relay or it's on the raged edge of
conduction it might not work as well as it should. I would try dumping the
relay and putting the alarm device in series with the collector and Vcc.
Jim
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Electronics_101-unsubscribe@...
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To unsubscribe from this group, send an
email
to:
Electronics_101-unsubscribe@...
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|
Hey ,
?
What so funny about this...?? if there is then
please do let me know of it...:-)
?
Regards :-),
?
--himanshu sharma
toggle quoted message
Show quoted text
Hey ,
?
put a 555 circuit in front of it in monostable
mode that will give a desired time for the switch to be on....
?
LOL.... this reminds me of time-bomb
!
?
|
