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1V vs 1.5V

T

Test

Jan 1, 1970
0
I have a motion detector that I want to get info to my computer. I am using LPT
port to input data. I could not follow what tripped motion. It has a LED which
lights up when it detects motion. I measured 1V DC when its "off" and 1.5 when
it's "on".

What kind of cirquit should I have? On the LPT side a register is on when a
couple of pins are short cirquited.
 
T

Test

Jan 1, 1970
0
BobW said:
Cirquit? Acquit? Circuit?

Either way, best to use a simple comparator with a 1.25V threshold.

Bob

Thanks.

(English is not my native language btw)
 
I

ian field

Jan 1, 1970
0
Test said:
I have a motion detector that I want to get info to my computer. I am using
LPT
port to input data. I could not follow what tripped motion. It has a LED
which
lights up when it detects motion. I measured 1V DC when its "off" and 1.5
when
it's "on".

What kind of cirquit should I have? On the LPT side a register is on when
a
couple of pins are short cirquited.

It seems a bit pointless for such a sensor to not have an output such as a
set of relay contacts, but if the only output is an indicator LED then the
simplest possible interface is to replace that LED with the LED section of
an optocoupler - that gives you an output in the form of a photo-transistor
which is controlled by the LED, with the advantage that its also
electrically isolated.

If you need the LED indication then include the LED in the collector load of
the photo-transistor.
 
J

Jon Slaughter

Jan 1, 1970
0
Test said:
I have a motion detector that I want to get info to my computer. I am using
LPT
port to input data. I could not follow what tripped motion. It has a LED
which
lights up when it detects motion. I measured 1V DC when its "off" and 1.5
when
it's "on".

What kind of cirquit should I have? On the LPT side a register is on when
a
couple of pins are short cirquited.

A simple comparator will do the job. Set it up so that it returns 5 volts
when past 1.25V and 0 volts when below 1.25V. You can hook it directly to
the parallel port.
 
J

Jamie

Jan 1, 1970
0
Test said:
I have a motion detector that I want to get info to my computer. I am using LPT
port to input data. I could not follow what tripped motion. It has a LED which
lights up when it detects motion. I measured 1V DC when its "off" and 1.5 when
it's "on".

What kind of cirquit should I have? On the LPT side a register is on when a
couple of pins are short cirquited.
Use an "Optocoupler" in it's place. it'll work perfectly.

http://www.fairchildsemi.com/an/AN/AN-3001.pdf
http://www.jaycar.com.au/images_uploaded/optocoup.pdf
http://www.vishay.com/optocouplers/

That should give you some idea's

http://webpages.charter.net/jamie_5"
 
T

Test

Jan 1, 1970
0
ian field said:
It seems a bit pointless for such a sensor to not have an output such as a
set of relay contacts, but if the only output is an indicator LED then the
simplest possible interface is to replace that LED with the LED section of
an optocoupler - that gives you an output in the form of a photo-transistor
which is controlled by the LED, with the advantage that its also
electrically isolated.

If you need the LED indication then include the LED in the collector load of
the photo-transistor.

I have a couple optocouplers
(ohttp://pdf1.alldatasheet.com/datasheet-pdf/view/2847/MOTOROLA/4N29.html) I
could use. But frankly I don't seem to get anything out of them. From the spec it
looks like I should apply 3V current to pin 1 and 2. In return I should get
something out of pins 6, 5 or 4. What? Resistance remains full at 4 and 5 no
matter what I do. Voltage is zero at them.
 
D

default

Jan 1, 1970
0
I have a motion detector that I want to get info to my computer. I am using LPT
port to input data. I could not follow what tripped motion. It has a LED which
lights up when it detects motion. I measured 1V DC when its "off" and 1.5 when
it's "on".

What kind of cirquit should I have? On the LPT side a register is on when a
couple of pins are short cirquited.

It takes 2.3 volts or so to light a red led so there's a good chance
that there's a better place to be taking the output from the motion
detector - one that offers more of a swing.
 
I

ian field

Jan 1, 1970
0
Test said:
I have a couple optocouplers
(ohttp://pdf1.alldatasheet.com/datasheet-pdf/view/2847/MOTOROLA/4N29.html)
I
could use. But frankly I don't seem to get anything out of them. From the
spec it
looks like I should apply 3V current to pin 1 and 2. In return I should
get
something out of pins 6, 5 or 4. What? Resistance remains full at 4 and 5
no
matter what I do. Voltage is zero at them.

Pins 4 & 5 are not a voltage generator - they are collector & emitter of the
photo-transistor illuminated by the LED on pins 1 & 2, connect the emitter
to GND and collector to Vcc via a 4k7 resistor - the output is then on the
collector.

If you've applied 3V to pins 1 & 2 you've most likely destroyed the LED so
that optocoupler is scrap. The current through the LED must be limited
usually between 20 - 50mA depending on type.
 
T

terryS

Jan 1, 1970
0
I see. I guess since most of us Americans only speak one language, we expect
everyone who speaks multiple languages to get OURS right. :)

Good luck with your project.

Bob

Who says Americans can 'speak' English? :) :)

There was a war of separation (Oops 'Independence') couple of hundred
years ago just to prove that it was so?

So citizens of the USA are now classed as 'Aliens' in, for example,
European countries!

But the British, who I guess we can assume developed the language and
have been working on it since long before Chaucer and Shakespeare
etc. just talk louder when someone doesn't understand them!

But 'Entente Cordiale' still applies and we remain, as some wit
observed, "Separated by the one common language (English)".

Regards to all from a mid-point, Canada! Where incidentally a
significant part of the population speaks French; another European
language. And after all if it's technical doesn't matter what language
it's in. Eh?

PS. Everybody applying for their passports?
 
T

Test

Jan 1, 1970
0
[snip]
Pins 4 & 5 are not a voltage generator - they are collector & emitter of the
photo-transistor illuminated by the LED on pins 1 & 2, connect the emitter
to GND and collector to Vcc via a 4k7 resistor - the output is then on the
collector.

If you've applied 3V to pins 1 & 2 you've most likely destroyed the LED so
that optocoupler is scrap. The current through the LED must be limited
usually between 20 - 50mA depending on type.

Thanks,

Is this what I should:
+-------+
| |
pin 1 -------+ +------ pin 6
| |
pin 2 -------+ +------ pin 5 <--- 4.7 K <---- Vcc (3V)
| |
pin 3 -------+ +------ pin 4 ------> Ground
| |
+-------+

What should happen in pins 1,2 and 6?

I am new to electronics. Thank you for your patience.
 
I

ian field

Jan 1, 1970
0
Test said:
[snip]
Pins 4 & 5 are not a voltage generator - they are collector & emitter of
the
photo-transistor illuminated by the LED on pins 1 & 2, connect the emitter
to GND and collector to Vcc via a 4k7 resistor - the output is then on the
collector.

If you've applied 3V to pins 1 & 2 you've most likely destroyed the LED so
that optocoupler is scrap. The current through the LED must be limited
usually between 20 - 50mA depending on type.

Thanks,

Is this what I should:
+-------+
| |
pin 1 -------+ +------ pin 6
| |
pin 2 -------+ +------ pin 5 <--- 4.7 K <---- Vcc (3V)
| |
pin 3 -------+ +------ pin 4 ------> Ground
| |
+-------+

What should happen in pins 1,2 and 6?

I am new to electronics. Thank you for your patience.

Pin 1 is the LED anode & pin 2 is LED cathode - a current between 20 & 50mA
should be passed from anode to cathode to illuminate the phototransistor and
switch it on.

Usually pin 6 is the base terminal of the phototransistor but if the
opto-coupler is a "circuit pull" from an old PSU it might have no internal
connection to pin 6, for what you're trying to do that shouldn't matter.
 
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