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grosseair(at)comcast.net
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 Posted: Wed Jun 15, 2011 4:33 pm Post subject: Photo FET Optocoupler |
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I have a pressure gauge that outputs a 5 VDC 10 mA signal. I need it to
turn on a bulb that draws 28 mA. I can't find a suitable relay, but I
was thinking that a photo FET optocoupler might work. The problem is
that I have no experience with these, and although I understand how they
work, I don't know how to find a particular one that will work with my
application. Could anyone suggest a part number for me? It would be
appreciated.
John Grosse
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enginerdy(at)gmail.com
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| Posted: Wed Jun 15, 2011 5:38 pm Post subject: Photo FET Optocoupler |
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How about a radioshack 2N2222 BJT transistor?
Feed your signal into a 2.2K resistor.
Other side of 2.2K resistor goes into the transistor base (B) terminal.
+12V (or 5V) power into the bulb
bulb to the collector (C) of the transistor
Emitter (E) of the transistor to ground
You can give it a rough test using a 5v source (or 3 AA batteries for 4.5V) and a 470 Ohm resistor.
Hope that helps!
--Daniel
On Jun 15, 2011, at 7:30 PM, John Grosse wrote:
| Quote: |
I have a pressure gauge that outputs a 5 VDC 10 mA signal. I need it to turn on a bulb that draws 28 mA. I can't find a suitable relay, but I was thinking that a photo FET optocoupler might work. The problem is that I have no experience with these, and although I understand how they work, I don't know how to find a particular one that will work with my application. Could anyone suggest a part number for me? It would be appreciated.
John Grosse
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nuckolls.bob(at)aeroelect
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| Posted: Wed Jun 15, 2011 6:57 pm Post subject: Photo FET Optocoupler |
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At 08:30 PM 6/15/2011, you wrote:
| Quote: | --> AeroElectric-List message posted by: John Grosse <grosseair(at)comcast.net>
I have a pressure gauge that outputs a 5 VDC 10 mA signal. I need it to turn on a bulb that draws 28 mA. I can't find a suitable relay, but I was thinking that a photo FET optocoupler might work. The problem is that I have no experience with these, and although I understand how they work, I don't know how to find a particular one that will work with my application. Could anyone suggest a part number for me? It would be appreciated. |
Doesn't need to be a photo-fet. There are plenty of LED
couplers that would work. Is the 5v output measured with
respect to ground . . . and does it go to zero volts
in the off state? Can you turn the bulb on by pulling
its control lead to ground? 28 mA lamp sounds like an
LED, no?
[img]cid:7.1.0.9.0.20110615224606.0202c1f0(at)aeroelectric.com.0[/img]
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Wed Jun 15, 2011 7:00 pm Post subject: Photo FET Optocoupler |
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At 08:30 PM 6/15/2011, you wrote:
| Quote: | --> AeroElectric-List message posted by: John Grosse <grosseair(at)comcast.net>
I have a pressure gauge that outputs a 5 VDC 10 mA signal. I need it to turn on a bulb that draws 28 mA. I can't find a suitable relay, but I was thinking that a photo FET optocoupler might work. The problem is that I have no experience with these, and although I understand how they work, I don't know how to find a particular one that will work with my application. Could anyone suggest a part number for me? It would be appreciated. |
Doesn't need to be a photo-fet. There are plenty of LED
couplers that would work. Is the 5v output measured with
respect to ground . . . and does it go to zero volts
in the off state? Can you turn the bulb on by pulling
its control lead to ground? 28 mA lamp sounds like an
LED, no?
[img]cid:7.1.0.9.0.20110615225649.02041e00(at)aeroelectric.com.1[/img]
OOPS! You said pressure gage? Is this output a linear
voltage that represents pressure or some voltage that is
zero some times and 5v other times?
Bob . . .
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grosseair(at)comcast.net
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| Posted: Thu Jun 16, 2011 7:14 am Post subject: Photo FET Optocoupler |
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The voltage from the gauge is +5v or 0 with respect to ground. The bulb
is incandescent: 140 mW at 5 VDC, but that was what I was going to use
when I thought a direct connection to the gauge would work. Now I'll use
a #73 which is 1.12W at 14 VDC . Yes I can turn the bulb on by pulling
it to ground.
John
| Quote: | ------------------------------------------------------------------------
Robert L. Nuckolls, III <mailto:nuckolls.bob(at)aeroelectric.com>
June 15, 2011 9:57 PM
At 08:30 PM 6/15/2011, you wrote:
Doesn't need to be a photo-fet. There are plenty of LED
couplers that would work. Is the 5v output measured with
respect to ground . . . and does it go to zero volts
in the off state? Can you turn the bulb on by pulling
its control lead to ground? 28 mA lamp sounds like an
LED, no?
Emacs!
OOPS! You said pressure gage? Is this output a linear
voltage that represents pressure or some voltage that is
zero some times and 5v other times?
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Thu Jun 16, 2011 7:23 am Post subject: Photo FET Optocoupler |
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At 11:11 AM 6/16/2011, you wrote:
| Quote: |
The voltage from the gauge is +5v or 0 with respect to ground. The
bulb is incandescent: 140 mW at 5 VDC, but that was what I was going
to use when I thought a direct connection to the gauge would work.
Now I'll use a #73 which is 1.12W at 14 VDC . Yes I can turn the
bulb on by pulling it to ground.
|
The the single transistor buffer suggested by myself
and others is a practical solution.
Bob . . .
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grosseair(at)comcast.net
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| Posted: Thu Jun 16, 2011 8:39 am Post subject: Photo FET Optocoupler |
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I'm curious why Daniel recommended a 2.2K resistor and you suggested a
1K resistor.
Thanks to both for your suggestions. This looks like it should work for
me well.
John
| Quote: | ------------------------------------------------------------------------
Robert L. Nuckolls, III <mailto:nuckolls.bob(at)aeroelectric.com>
June 16, 2011 10:20 AM
<nuckolls.bob(at)aeroelectric.com>
The the single transistor buffer suggested by myself
and others is a practical solution.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Thu Jun 16, 2011 8:46 am Post subject: Photo FET Optocoupler |
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At 12:34 PM 6/16/2011, you wrote:
| Quote: |
I'm curious why Daniel recommended a 2.2K resistor and you suggested
a 1K resistor.
|
Not critical. Throw a dart and anything from 1k to 50K would probably
work.
Bob . . .
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enginerdy(at)gmail.com
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| Posted: Thu Jun 16, 2011 10:34 am Post subject: Photo FET Optocoupler |
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I actually thought about it, changed to a 1K, then changed back to a
2.2K before I sent it. I guess I just like the color red.. haha
On Thu, Jun 16, 2011 at 11:43 AM, Robert L. Nuckolls, III
<nuckolls.bob(at)aeroelectric.com> wrote:
| Quote: |
<nuckolls.bob(at)aeroelectric.com>
At 12:34 PM 6/16/2011, you wrote:
>
>
> <grosseair(at)comcast.net>
>
> I'm curious why Daniel recommended a 2.2K resistor and you suggested a 1K
> resistor.
Not critical. Throw a dart and anything from 1k to 50K would probably
work.
Bob . . .
|
--
Daniel Hooper
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