| Author |
Message |
anwar
Guest
|
 Posted:
Mon Feb 14, 2005 1:22 am Post subject:
How to design an infra-red circuit to detect small obstacle |
|
|
Hi,
I am trying to figure out how to design a simple infra-red circuit
so that it can detect any small obstacle placed/passed in between
infra-red receiver/transmitter. I want a light to turn on or whatever
else to happen when this obstacle is detected.
The distance between receiver/transmitter will be maximum 2 feet and
minimum 6 inch.
Thanks,
Anwar
http://www.bluehawk.biz
http://www.bluemela.com
|
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|
 |
Spehro Pefhany
Guest
|
| Posted:
Mon Feb 14, 2005 1:35 am Post subject:
Re: How to design an infra-red circuit to detect small obsta |
|
|
On 13 Feb 2005 11:22:57 -0800, the renowned "anwar"
<anwar09@yahoo.com> wrote:
| Quote: | Hi,
I am trying to figure out how to design a simple infra-red circuit
so that it can detect any small obstacle placed/passed in between
infra-red receiver/transmitter. I want a light to turn on or whatever
else to happen when this obstacle is detected.
The distance between receiver/transmitter will be maximum 2 feet and
minimum 6 inch.
|
You might want to look at safety devices for punch presses etc. I
think they use an array of emitters and detectors.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com |
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|
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Larry Brasfield
Guest
|
| Posted:
Mon Feb 14, 2005 3:34 am Post subject:
Re: How to design an infra-red circuit to detect small obsta |
|
|
"anwar" <anwar09@yahoo.com> wrote in message
news:1108322577.860629.36920@c13g2000cwb.googlegroups.com...
| Quote: | Hi,
Hi.
I am trying to figure out how to design a simple infra-red circuit
so that it can detect any small obstacle placed/passed in between
infra-red receiver/transmitter. I want a light to turn on or whatever
else to happen when this obstacle is detected.
|
It would help if you stated what optical setup you
have in mind. Would it be enough to detect that
a narrow beam has been interrupted?
| Quote: | The distance between receiver/transmitter will be maximum 2 feet and
minimum 6 inch.
|
A simple way to make a fairly sensitive transceiver
and detector is to use a NE567 tone decoder.
Depending on the gain you need, an additional
op-amp stage might be needed or you can use
a phototransistor as a gain element with suitable
external components.
This virtues of this technique are low parts count and
relative insensitivity to DC or line frequency light.
If this interests you, say so and I'll provide such
details as are not obvious.
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.
|
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|
|
anwar
Guest
|
| Posted:
Mon Feb 14, 2005 4:24 am Post subject:
Re: How to design an infra-red circuit to detect small obsta |
|
|
Larry,
- I do need a narrom detection indeed. So if I have a 2 feet
separation and there is a narrow beam where if someone place a finger
or pass his finger thru the narrow beam quickly it should detect that.
- As per level of gain- I need to make a sound of a certain frequency
when the obstacle is detected.
So, if you can please provide me details on how to make a circuit like
that it will be wonderful.
Thanks,
Anwar
http://www.bluehawk.biz
http://www.bluemela.com |
|
| Back to top |
|
|
John Larkin
Guest
|
| Posted:
Mon Feb 14, 2005 4:34 am Post subject:
Re: How to design an infra-red circuit to detect small obsta |
|
|
On Sun, 13 Feb 2005 13:34:22 -0800, "Larry Brasfield"
<donotspam_larry_brasfield@hotmail.com> wrote:
| Quote: |
"anwar" <anwar09@yahoo.com> wrote in message
news:1108322577.860629.36920@c13g2000cwb.googlegroups.com...
Hi,
Hi.
I am trying to figure out how to design a simple infra-red circuit
so that it can detect any small obstacle placed/passed in between
infra-red receiver/transmitter. I want a light to turn on or whatever
else to happen when this obstacle is detected.
It would help if you stated what optical setup you
have in mind. Would it be enough to detect that
a narrow beam has been interrupted?
The distance between receiver/transmitter will be maximum 2 feet and
minimum 6 inch.
A simple way to make a fairly sensitive transceiver
and detector is to use a NE567 tone decoder.
Depending on the gain you need, an additional
op-amp stage might be needed or you can use
a phototransistor as a gain element with suitable
external components.
This virtues of this technique are low parts count and
relative insensitivity to DC or line frequency light.
If this interests you, say so and I'll provide such
details as are not obvious.
|
You can buy the little receiver blocks like TV sets use. They detect
modulated IR, very sensitive, 40 KHz or something. The transmitting
LED could be modulated by - gasp - a 555 or something.
John |
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|
|
Larry Brasfield
Guest
|
| Posted:
Mon Feb 14, 2005 5:11 am Post subject:
Re: How to design an infra-red circuit to detect small obsta |
|
|
"anwar" <anwar09@yahoo.com> wrote in message
news:1108333459.965812.199980@o13g2000cwo.googlegroups.com...
| Quote: | Larry,
- I do need a narrom detection indeed. So if I have a 2 feet
separation and there is a narrow beam where if someone place a finger
or pass his finger thru the narrow beam quickly it should detect that.
- As per level of gain- I need to make a sound of a certain frequency
when the obstacle is detected.
So, if you can please provide me details on how to make a circuit like
that it will be wonderful.
|
I'm not going to do the detail design or any simulation
on this. I have built similar circuits and used the NE567
in this manner, so I can assure you that this technique
will work with appropriate design and adjustments for
your specific application.
The NE567 provides these functional blocks:
1. An RC oscillator with a useful semi-digital output on
pin 5. This can drive a low-power LED directly or, with
an extra transistor, as much as your LED can take.
2. A synchronous demodulator, multiplying the signal on
pin 3 to produce filtered baseband on pin 1. You can
set the demodulator bandwidth according to how fast
you want detection to happen versus how much out-of-
band noise you wish to reject.
3. A reference and comparator to detect when the level
on pin 3 exceeds a threshold, producing an open-collector
output on pin 8.
You most likely need to provide some gain between the
photocurrent signal and pin 3 of the NE567. The net
response of that stage, from photo-current to pin 3,
should have 90 degrees of phase shift to work well
with the NE567 demodulator. (That might be 270
degrees, so the LED might have to be turned around
or the polarity of its BJT driver inverted.) For modest
gain, a phototransistor can be used in a circuit with the
following topology to provide this function:
VCC
+
|
.-.
| |
| |
'.'
.---------o
| | ||
.-. o------||- PhotoRx
| | | ||
| | |
'-' |
| |/
o-------|
.----o |>
| | |
--- .-. o---.
--- | | | |
| | | .-. |
| '-' | | ---
| | | | ---
'----o '-' |
| o---'
| |
=== ===
GND GND
(created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)
This can be done with a very compact layout near the
receiving phototransistor to minimize noise pickup. The
LED can be driven by some twisted pair.
As for making a tone when pin 8 is driven low by
detection of the beam, (or opened by interruption
of the beam), I will leave that problem to you.
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me. |
|
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|
|
Larry Brasfield
Guest
|
| Posted:
Mon Feb 14, 2005 5:19 am Post subject:
Re: How to design an infra-red circuit to detect small obsta |
|
|
"John Larkin" <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote in
message news:lalv015427a6uoin3733mbd7qfkf034059@4ax.com...
| Quote: | On Sun, 13 Feb 2005 13:34:22 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:
....
A simple way to make a fairly sensitive transceiver
and detector is to use a NE567 tone decoder.
Depending on the gain you need, an additional
op-amp stage might be needed or you can use
a phototransistor as a gain element with suitable
external components.
This virtues of this technique are low parts count and
relative insensitivity to DC or line frequency light.
....
You can buy the little receiver blocks like TV sets use. They detect
modulated IR, very sensitive, 40 KHz or something. The transmitting
LED could be modulated by - gasp - a 555 or something.
|
What I like about the NE567 for this purpose is that
the detection bandwidth can be adjusted and carrier
frequency adjusted up to a hundred kHz or so. The
circuitry is quite generic and compact. And there is no
issue trying to match transmit and receive frequency,
even if low precision parts are used.
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me. |
|
| Back to top |
|
|
Larry Brasfield
Guest
|
| Posted:
Mon Feb 14, 2005 6:10 am Post subject:
Re: How to design an infra-red circuit to detect small obsta |
|
|
<Geodanah@yahoo.com> wrote in message
news:1108352409.182615.71790@g14g2000cwa.googlegroups.com...
| Quote: |
anwar wrote:
Hi,
I am trying to figure out how to design a simple infra-red circuit
so that it can detect any small obstacle placed/passed in between
infra-red receiver/transmitter. I want a light to turn on or whatever
else to happen when this obstacle is detected.
The distance between receiver/transmitter will be maximum 2 feet and
minimum 6 inch.
....
I'm just an EE student right now, so I am trying to learn from this
question. Please tell me what is wrong. That being said:
Why does the IR beam have to be modulated? What would be wrong with
just putting a straight IR beam (IR LED with a lens?) hitting an IR
photodiode or phototransitor. Invert the signal from that (just hook up
the connection at the collector of the phototransistor), and hook it up
to an LED or relay for the indicator light.
|
With careful attention to the optics and in a benign
environment, that might work. Using modulated
light and narrowband detection, problems with
ambient light can be easily precluded and the
effort to build that circuit is comparable to or
easier than getting optics designed and aligned
to respond only to the intended beam.
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me. |
|
| Back to top |
|
|
Guest
|
| Posted:
Mon Feb 14, 2005 6:11 am Post subject:
Re: How to design an infra-red circuit to detect small obsta |
|
|
anwar wrote:
| Quote: | Hi,
I am trying to figure out how to design a simple infra-red circuit
so that it can detect any small obstacle placed/passed in between
infra-red receiver/transmitter. I want a light to turn on or whatever
else to happen when this obstacle is detected.
The distance between receiver/transmitter will be maximum 2 feet and
minimum 6 inch.
Thanks,
Anwar
http://www.bluehawk.biz
http://www.bluemela.com
|
I'm just an EE student right now, so I am trying to learn from this
question. Please tell me what is wrong. That being said:
Why does the IR beam have to be modulated? What would be wrong with
just putting a straight IR beam (IR LED with a lens?) hitting an IR
photodiode or phototransitor. Invert the signal from that (just hook up
the connection at the collector of the phototransistor), and hook it up
to an LED or relay for the indicator light. |
|
| Back to top |
|
|
Brian
Guest
|
| Posted:
Mon Feb 14, 2005 1:56 pm Post subject:
Re: How to design an infra-red circuit to detect small obsta |
|
|
I think Holtek makes IR transmitter ic's that would work well too.
"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in message
news:D8RPd.479$Kd4.1654@news.uswest.net...
| Quote: | "anwar" <anwar09@yahoo.com> wrote in message
news:1108333459.965812.199980@o13g2000cwo.googlegroups.com...
Larry,
- I do need a narrom detection indeed. So if I have a 2 feet
separation and there is a narrow beam where if someone place a finger
or pass his finger thru the narrow beam quickly it should detect that.
- As per level of gain- I need to make a sound of a certain frequency
when the obstacle is detected.
So, if you can please provide me details on how to make a circuit like
that it will be wonderful.
I'm not going to do the detail design or any simulation
on this. I have built similar circuits and used the NE567
in this manner, so I can assure you that this technique
will work with appropriate design and adjustments for
your specific application.
The NE567 provides these functional blocks:
1. An RC oscillator with a useful semi-digital output on
pin 5. This can drive a low-power LED directly or, with
an extra transistor, as much as your LED can take.
2. A synchronous demodulator, multiplying the signal on
pin 3 to produce filtered baseband on pin 1. You can
set the demodulator bandwidth according to how fast
you want detection to happen versus how much out-of-
band noise you wish to reject.
3. A reference and comparator to detect when the level
on pin 3 exceeds a threshold, producing an open-collector
output on pin 8.
You most likely need to provide some gain between the
photocurrent signal and pin 3 of the NE567. The net
response of that stage, from photo-current to pin 3,
should have 90 degrees of phase shift to work well
with the NE567 demodulator. (That might be 270
degrees, so the LED might have to be turned around
or the polarity of its BJT driver inverted.) For modest
gain, a phototransistor can be used in a circuit with the
following topology to provide this function:
VCC
+
|
.-.
| |
| |
'.'
.---------o
| | ||
.-. o------||- PhotoRx
| | | ||
| | |
'-' |
| |/
o-------|
.----o |
| | |
--- .-. o---.
--- | | | |
| | | .-. |
| '-' | | ---
| | | | ---
'----o '-' |
| o---'
| |
=== ===
GND GND
(created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)
This can be done with a very compact layout near the
receiving phototransistor to minimize noise pickup. The
LED can be driven by some twisted pair.
As for making a tone when pin 8 is driven low by
detection of the beam, (or opened by interruption
of the beam), I will leave that problem to you.
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.
|
|
|
| Back to top |
|
|
Brian
Guest
|
| Posted:
Mon Feb 14, 2005 1:59 pm Post subject:
Re: How to design an infra-red circuit to detect small obsta |
|
|
<Geodanah@yahoo.com> wrote in message
news:1108352409.182615.71790@g14g2000cwa.googlegroups.com...
| Quote: |
anwar wrote:
Hi,
I am trying to figure out how to design a simple infra-red circuit
so that it can detect any small obstacle placed/passed in between
infra-red receiver/transmitter. I want a light to turn on or whatever
else to happen when this obstacle is detected.
The distance between receiver/transmitter will be maximum 2 feet and
minimum 6 inch.
Thanks,
Anwar
http://www.bluehawk.biz
http://www.bluemela.com
I'm just an EE student right now, so I am trying to learn from this
question. Please tell me what is wrong. That being said:
Why does the IR beam have to be modulated? What would be wrong with
just putting a straight IR beam (IR LED with a lens?) hitting an IR
photodiode or phototransitor. Invert the signal from that (just hook up
the connection at the collector of the phototransistor), and hook it up
to an LED or relay for the indicator light.
|
Detecting IR at one modulated frequency reduces the ambient noise greatly,
higher signal to noise. That allows you to drop power levels, etc., and
still get it to work under all conditions. |
|
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|
|
|
|
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