Optoisolator needs inverting
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Posts: 46,084
Hello,
I'm trying to use an optoisolator to receive input from a stamp output pin, and
then have the optoisolator turn on a linear power regulator chip by connecting
it to the regulator's shutdown pin. When the shutdown pin is pulled low, it
turns off.
My problem is that all of the examples I've seen using optoisolators tie the
transistor emitter to ground, and the collector is the output which is tied to
+5 so that the switch is inverted. I'd like to set it up so that when the stamp
activates the optoisolator (through the internel LED) the output of the isolator
goes high.
Although I haven't seen any examples, can the transistor emitter be tied to
ground through a pull-down resistor, and the collector connected to +5? The
regulator shutdown pin would then connect to the emitter so that it is pulled
down to ground, except when the stamp output is high.
I know this method wouldn't work for driving loads, but the regulator shutdown
pin requires almost no current. Will this work? Suggestions?
Thanks,
Stewart
I'm trying to use an optoisolator to receive input from a stamp output pin, and
then have the optoisolator turn on a linear power regulator chip by connecting
it to the regulator's shutdown pin. When the shutdown pin is pulled low, it
turns off.
My problem is that all of the examples I've seen using optoisolators tie the
transistor emitter to ground, and the collector is the output which is tied to
+5 so that the switch is inverted. I'd like to set it up so that when the stamp
activates the optoisolator (through the internel LED) the output of the isolator
goes high.
Although I haven't seen any examples, can the transistor emitter be tied to
ground through a pull-down resistor, and the collector connected to +5? The
regulator shutdown pin would then connect to the emitter so that it is pulled
down to ground, except when the stamp output is high.
I know this method wouldn't work for driving loads, but the regulator shutdown
pin requires almost no current. Will this work? Suggestions?
Thanks,
Stewart
Comments
collector) pulled high, then goes low through the NPN transistor when it
conducts. If you flip things around so that the collector ties right to
Vdd, the emitter is pulled-down to Vss, and your isolated output
connects to the emitter (between the emitter and pull-down), you'll be
good to go. When the transistor conducts you'll get Vdd across the
pull-down which will be present at your output line (about Vdd - 0.7,
depending on the transistor).
-- Jon Williams
-- Applications Engineer, Parallax
-- Dallas Office
Original Message
From: Stewart Mayer [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=qsdmYQqkfW0pbgW4MU10IAn6gZ8_-BK-vALXNIpCEGQyh8wy2u067dh7Y7IgJAIfSDaGp0uTYHdH8GEc43IUmsrh-HA4]stamplist@k...[/url
Sent: Wednesday, February 11, 2004 11:10 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Optoisolator needs inverting
Hello,
I'm trying to use an optoisolator to receive input from a stamp output
pin, and
then have the optoisolator turn on a linear power regulator chip by
connecting
it to the regulator's shutdown pin. When the shutdown pin is pulled
low, it
turns off.
My problem is that all of the examples I've seen using optoisolators tie
the
transistor emitter to ground, and the collector is the output which is
tied to
+5 so that the switch is inverted. I'd like to set it up so that when
+the stamp
activates the optoisolator (through the internel LED) the output of the
isolator
goes high.
Although I haven't seen any examples, can the transistor emitter be tied
to
ground through a pull-down resistor, and the collector connected to +5?
The
regulator shutdown pin would then connect to the emitter so that it is
pulled
down to ground, except when the stamp output is high.
I know this method wouldn't work for driving loads, but the regulator
shutdown
pin requires almost no current. Will this work? Suggestions?
Thanks,
Stewart
the group files section.
High-High_Opto.JPG
-- Jon Williams
-- Parallax
Original Message
From: Jon Williams
Sent: Wednesday, February 11, 2004 11:42 AM
To: basicstamps@yahoogroups.com
Subject: RE: [noparse][[/noparse]basicstamps] Optoisolator needs inverting
As you indicate, the *usual* configuration has the output (tied to
collector) pulled high, then goes low through the NPN transistor when it
conducts. If you flip things around so that the collector ties right to
Vdd, the emitter is pulled-down to Vss, and your isolated output
connects to the emitter (between the emitter and pull-down), you'll be
good to go. When the transistor conducts you'll get Vdd across the
pull-down which will be present at your output line (about Vdd - 0.7,
depending on the transistor).
-- Jon Williams
-- Applications Engineer, Parallax
-- Dallas Office
Original Message
From: Stewart Mayer [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=obkQNkufkwJKWjTuHOUUTkIIO54NOq_LlcCrwBjvdCoMG4I_dm18CqtDGp_GWUTty_STtU0AFR8_GTnHF-q4RefdGTw]stamplist@k...[/url
Sent: Wednesday, February 11, 2004 11:10 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Optoisolator needs inverting
Hello,
I'm trying to use an optoisolator to receive input from a stamp output
pin, and
then have the optoisolator turn on a linear power regulator chip by
connecting
it to the regulator's shutdown pin. When the shutdown pin is pulled
low, it
turns off.
My problem is that all of the examples I've seen using optoisolators tie
the
transistor emitter to ground, and the collector is the output which is
tied to
+5 so that the switch is inverted. I'd like to set it up so that when
+the stamp
activates the optoisolator (through the internel LED) the output of the
isolator
goes high.
Although I haven't seen any examples, can the transistor emitter be tied
to
ground through a pull-down resistor, and the collector connected to +5?
The
regulator shutdown pin would then connect to the emitter so that it is
pulled
down to ground, except when the stamp output is high.
I know this method wouldn't work for driving loads, but the regulator
shutdown
pin requires almost no current. Will this work? Suggestions?
Thanks,
Stewart
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Thanks so much!
stewart
On Wed, 11 Feb 2004 09:53:57 -0800, Jon Williams wrote:
> In case my description isn't quite clear, I've uploaded a schematic to
> the group files section.
>
> High-High_Opto.JPG
>
> -- Jon Williams
> -- Parallax
>
>
>
Original Message
> From: Jon Williams
> Sent: Wednesday, February 11, 2004 11:42 AM
> To: basicstamps@yahoogroups.com
> Subject: RE: [noparse][[/noparse]basicstamps] Optoisolator needs inverting
>
>
> As you indicate, the *usual* configuration has the output (tied to
> collector) pulled high, then goes low through the NPN transistor when it
> conducts. If you flip things around so that the collector ties right to
> Vdd, the emitter is pulled-down to Vss, and your isolated output
> connects to the emitter (between the emitter and pull-down), you'll be
> good to go. When the transistor conducts you'll get Vdd across the
> pull-down which will be present at your output line (about Vdd - 0.7,
> depending on the transistor).
>
> -- Jon Williams
> -- Applications Engineer, Parallax
> -- Dallas Office
>
>
>
Original Message
> From: Stewart Mayer [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=qWsmj7m_p5QcKhlpPTFClDCNvtcnFNo8Ol8HD1Yr1tZALcnTf1RH8AwkPS4vQjHhBSEFVxTrmNwAnkDPomrcmoaL37vP]stamplist@k...[/url
> Sent: Wednesday, February 11, 2004 11:10 AM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Optoisolator needs inverting
>
>
> Hello,
>
> I'm trying to use an optoisolator to receive input from a stamp output
> pin, and
> then have the optoisolator turn on a linear power regulator chip by
> connecting
> it to the regulator's shutdown pin. When the shutdown pin is pulled
> low, it
> turns off.
>
> My problem is that all of the examples I've seen using optoisolators tie
> the
> transistor emitter to ground, and the collector is the output which is
> tied to
> +5 so that the switch is inverted. I'd like to set it up so that when
> +the stamp
> activates the optoisolator (through the internel LED) the output of the
> isolator
> goes high.
>
> Although I haven't seen any examples, can the transistor emitter be tied
> to
> ground through a pull-down resistor, and the collector connected to +5?
> The
> regulator shutdown pin would then connect to the emitter so that it is
> pulled
> down to ground, except when the stamp output is high.
>
> I know this method wouldn't work for driving loads, but the regulator
> shutdown
> pin requires almost no current. Will this work? Suggestions?
>
> Thanks,
> Stewart
>
>
> 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
>
>
> This message has been scanned by WebShield. Please report SPAM to
> abuse@p....
>
>
> To UNSUBSCRIBE, just send mail to:
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> from the same email address that you subscribed. Text in the Subject and Body
of the message
> will be ignored.
>
> Yahoo! Groups Links
>
>
>