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transistor switching question

ArchiverArchiver Posts: 46,084
edited 2003-06-19 17:26 in General Discussion
Okay, folks, I need advice from someone smarter than me, which shouldn't be
too difficult here. ;-) I'm a bit rusty with transistors, and I'm having
problems setting up one to act as a switch.

* I have an NPN transistor with a 100ohm resistor from the collector to
+12.
* The emitter is connected to ground via a relay coil (70ohm dc resistance,
75ma operating current).
* The coil has the appropriate transient protection diode.
* The base is has a 1.5k resistor which connects it to the stamp.

When the base is connected, via the resistor, directly to the 5v rail, it
turns the relay on and off as it should. I measured the base current at
around 620uA, and the base voltage was 5v.

I assumed this mean't the circuit would work with the bs/2's output levels,
and put the thing together on a board, but DING, it didn't. The bs/2's
output level of 3.8V just isn't enough to trigger the transistor.

I tried bypassing the 1.5k resistor, hoping an increased base current would
turn on the transistor, but nada.

I tried replacing the relay with an LED just to see if the transistor would
switch properly, and it did. The LED turns on and off with the stamp's
output level, but when I replaced it with the relay, nothing.

I measured the 3.8v at the base when the stamp was trying to drive it.

What the heck am I missing here? I though the thing would switch as soon as
the base voltage was about .6-.7 volts above the emitter. Is there some
minimum base current to collector current relationship I need to know about?

I know I could probably bypass the whole problem by simply driving the relay
with 5 volts, but now that the circuit is built (I didn't actually test
using the bs/2's output, I only connected the base of the transistor
directly to the 5volt rail, and, when that worked, assumed it would work
with the bs/2), I'd like to know what I'm missing. It seems like it should
work.

thanks,


d..

**************************************************************************
* David Okagaki dokagaki@w...
*
* "The light at the end of the tunnel is that of the on coming train!"
*
**************************************************************************

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2003-06-18 23:55
    Hi Dave,

    Here's the normal way to connect a small NPN transistor to switch a relay
    coil...

    Connect the NPN emitter to ground and the collector to one side of your
    relay coil. The other side of the relay coil connects to B+. Leave the
    transient protection diode across the relay coil. If the relay coil is
    rated to operate on +12 volts, you shouldn't need the 100 ohm resistor in
    series with it. If you need the resistor to drop the voltage because the
    relay is rated for a lower voltage, connect the resistor between +12 volts
    and the relay coil. You could also connect it between the other side of the
    relay coil and the collector, but you don't want it between the NPN's
    emitter and ground.

    Depending on the gain of your transistor, the 1.5k base resistor may be
    okay. You may need to go a little lower to get full saturation.... what
    transistor are you using?

    Based on what's happened so far, I'd start out with a fresh transistor ;-)
    The Stamp pin should drive this configuration nicely.

    Randy

    www.glitchbuster.com


    Original Message
    From: "Dave" <dokagaki@w...>
    To: <basicstamps@yahoogroups.com>
    Sent: Wednesday, June 18, 2003 3:38 PM
    Subject: [noparse][[/noparse]basicstamps] transistor switching question


    > Okay, folks, I need advice from someone smarter than me, which shouldn't
    be
    > too difficult here. ;-) I'm a bit rusty with transistors, and I'm having
    > problems setting up one to act as a switch.
    >
    > * I have an NPN transistor with a 100ohm resistor from the collector to
    > +12.
    > * The emitter is connected to ground via a relay coil (70ohm dc
    resistance,
    > 75ma operating current).
    > * The coil has the appropriate transient protection diode.
    > * The base is has a 1.5k resistor which connects it to the stamp.
    >
    > When the base is connected, via the resistor, directly to the 5v rail, it
    > turns the relay on and off as it should. I measured the base current at
    > around 620uA, and the base voltage was 5v.
    >
    > I assumed this mean't the circuit would work with the bs/2's output
    levels,
    > and put the thing together on a board, but DING, it didn't. The bs/2's
    > output level of 3.8V just isn't enough to trigger the transistor.
    >
    > I tried bypassing the 1.5k resistor, hoping an increased base current
    would
    > turn on the transistor, but nada.
    >
    > I tried replacing the relay with an LED just to see if the transistor
    would
    > switch properly, and it did. The LED turns on and off with the stamp's
    > output level, but when I replaced it with the relay, nothing.
    >
    > I measured the 3.8v at the base when the stamp was trying to drive it.
    >
    > What the heck am I missing here? I though the thing would switch as soon
    as
    > the base voltage was about .6-.7 volts above the emitter. Is there some
    > minimum base current to collector current relationship I need to know
    about?
    >
    > I know I could probably bypass the whole problem by simply driving the
    relay
    > with 5 volts, but now that the circuit is built (I didn't actually test
    > using the bs/2's output, I only connected the base of the transistor
    > directly to the 5volt rail, and, when that worked, assumed it would work
    > with the bs/2), I'd like to know what I'm missing. It seems like it
    should
    > work.
    >
    > thanks,
    >
    >
    > d..
    >
    > **************************************************************************
    > * David Okagaki dokagaki@w...
    > *
    > * "The light at the end of the tunnel is that of the on coming train!"
    > *
    > **************************************************************************
    >
    >
    > 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.
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2003-06-19 00:29
    In a message dated 6/18/2003 3:40:42 PM Pacific Daylight Time,
    dokagaki@w... writes:

    > Okay, folks, I need advice from someone smarter than me, which shouldn't be
    > too difficult here. ;-) I'm a bit rusty with transistors, and I'm having
    > problems setting up one to act as a switch.
    >
    > * I have an NPN transistor with a 100ohm resistor from the collector to
    > +12.
    > * The emitter is connected to ground via a relay coil (70ohm dc
    > resistance,
    > 75ma operating current).
    > * The coil has the appropriate transient protection diode.
    > * The base is has a 1.5k resistor which connects it to the stamp.
    >
    > When the base is connected, via the resistor, directly to the 5v rail, it
    > turns the relay on and off as it should. I measured the base current at
    > around 620uA, and the base voltage was 5v.
    >
    > I assumed this mean't the circuit would work with the bs/2's output levels,
    > and put the thing together on a board, but DING, it didn't. The bs/2's
    > output level of 3.8V just isn't enough to trigger the transistor.
    >
    > I tried bypassing the 1.5k resistor, hoping an increased base current would
    > turn on the transistor, but nada.
    >
    > I tried replacing the relay with an LED just to see if the transistor would
    > switch properly, and it did. The LED turns on and off with the stamp's
    > output level, but when I replaced it with the relay, nothing.
    >
    > I measured the 3.8v at the base when the stamp was trying to drive it.
    >
    > What the heck am I missing here? I though the thing would switch as soon as
    > the base voltage was about .6-.7 volts above the emitter. Is there some
    > minimum base current to collector current relationship I need to know about?
    >
    > I know I could probably bypass the whole problem by simply driving the relay
    > with 5 volts, but now that the circuit is built (I didn't actually test
    > using the bs/2's output, I only connected the base of the transistor
    > directly to the 5volt rail, and, when that worked, assumed it would work
    > with the bs/2), I'd like to know what I'm missing. It seems like it should
    > work.
    >
    > thanks,
    >
    >
    > d..
    >

    d,

    what is the transistor? 2n3904? or....
    From what I read in your post, the transistor should saturate....assuming the
    transistor has a Beta of 100 or more...

    Stamp output 3.8 minus Vbe of 0.7v leaves you with about 3v across 1.5k ohms
    which will give you 2 ma of "base drive" current. Multiply this 2 ma times
    beta (100) and you should be capable of 200ma of collector current which is more

    that what is need to drive your relay....

    But.....I would wire this differently........because the base voltage must be
    capable of being 0.7 volts more than it takes to turn the relay on....3.8
    from the stamp may not be high enough...

    Rewire as follows with a 2n3904 (almost guaranteed to work)

    Not sure why you have the 100 ohm resistor in the circuit.....

    Connect the relay coil to +12 volts and the other end of the relay coil to
    the collector. Connect emitter directly to ground....Make the NPN provide
    GROUND for your relay, NOT provide power, which is what your current
    configuration
    is trying to do......

    Write back with results


    [noparse][[/noparse]Non-text portions of this message have been removed]
  • ArchiverArchiver Posts: 46,084
    edited 2003-06-19 00:29
    I would not go as far as to say I am smarter than you but I would say that you
    are right. The transistor will turn on as soon as it's base voltage goes .7
    volts above the emitter. Problem is, that with the relay in the emitter
    circuit, the base has to go .7 volts above the voltage dropped across the relay
    coil. Simple fix, put the relay on the collector side.

    Leroy


    Original Message
    From: "Dave" <dokagaki@w...>
    To: <basicstamps@yahoogroups.com>
    Sent: Wednesday, June 18, 2003 6:38 PM
    Subject: [noparse][[/noparse]basicstamps] transistor switching question


    : Okay, folks, I need advice from someone smarter than me, which shouldn't be
    : too difficult here. ;-) I'm a bit rusty with transistors, and I'm having
    : problems setting up one to act as a switch.
    :
    : * I have an NPN transistor with a 100ohm resistor from the collector to
    : +12.
    : * The emitter is connected to ground via a relay coil (70ohm dc resistance,
    : 75ma operating current).
    : * The coil has the appropriate transient protection diode.
    : * The base is has a 1.5k resistor which connects it to the stamp.
    :
    : When the base is connected, via the resistor, directly to the 5v rail, it
    : turns the relay on and off as it should. I measured the base current at
    : around 620uA, and the base voltage was 5v.
    :
    : I assumed this mean't the circuit would work with the bs/2's output levels,
    : and put the thing together on a board, but DING, it didn't. The bs/2's
    : output level of 3.8V just isn't enough to trigger the transistor.
    :
    : I tried bypassing the 1.5k resistor, hoping an increased base current would
    : turn on the transistor, but nada.
    :
    : I tried replacing the relay with an LED just to see if the transistor would
    : switch properly, and it did. The LED turns on and off with the stamp's
    : output level, but when I replaced it with the relay, nothing.
    :
    : I measured the 3.8v at the base when the stamp was trying to drive it.
    :
    : What the heck am I missing here? I though the thing would switch as soon as
    : the base voltage was about .6-.7 volts above the emitter. Is there some
    : minimum base current to collector current relationship I need to know about?
    :
    : I know I could probably bypass the whole problem by simply driving the relay
    : with 5 volts, but now that the circuit is built (I didn't actually test
    : using the bs/2's output, I only connected the base of the transistor
    : directly to the 5volt rail, and, when that worked, assumed it would work
    : with the bs/2), I'd like to know what I'm missing. It seems like it should
    : work.
    :
    : thanks,
    :
    :
    : d..
    :
    : **************************************************************************
    : * David Okagaki dokagaki@w...
    : *
    : * "The light at the end of the tunnel is that of the on coming train!"
    : *
    : **************************************************************************
    :
    :
    : 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.
    :
    :
    : Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
    :
    :
  • ArchiverArchiver Posts: 46,084
    edited 2003-06-19 00:33
    In a message dated 6/18/2003 3:40:42 PM Pacific Daylight Time,
    dokagaki@w... writes:

    > Okay, folks, I need advice from someone smarter than me, which shouldn't be
    > too difficult here. ;-) I'm a bit rusty with transistors, and I'm having
    > problems setting up one to act as a switch.

    Let me try again a with a little more clarity.....

    Connect the base of the transistor to the stamp via 1.5 k ohms.

    Connect the emitter of the transistor to ground.

    Connect the collector of the transistor to one end of the relay coil.

    Connect the other end of the relay coil to +12 volts.

    Make sure you have your reverse spike diode across the relay coil with the
    correct polarity (cathode to +12v).

    If you use a 2n3904, it should definately work


    [noparse][[/noparse]Non-text portions of this message have been removed]
  • ArchiverArchiver Posts: 46,084
    edited 2003-06-19 01:40
    You have this transistor wired in a good configuration, called
    "emitter follower". It is a perfectly good circuit to drive a relay
    coil that would operate okay with 4--5 volts across it. The emitter
    follower, when appropriate, is the simplest possible current and
    power amplifier, and it is also very fast acting.

    I am confused by the bad result. With a 70 ohm coil and a power
    supply of 4.3 volts, the relay current would be would be 61 milliamps
    (4.3/70). You measured the base current of 0.62 mA with the
    transistor base connected directly to +5 volts, so the transistor
    gain is 61/0.62 = 100.

    >When the base is connected, via the resistor, directly to the 5v rail, it
    >turns the relay on and off as it should. I measured the base current at
    >around 620uA, and the base voltage was 5v.

    Check that again. The 620uA has to flow through the 1500 ohm
    resistor, dropping about 930 millivolts. So there is no way the base
    could have been at 5 volts with the other end of the resistor also at
    5 volts! The base would have been at about 4.07 volts. And the
    emitter would have been at 0.6 to 0.7 less than that, at about 3.4
    volts. And did you say that did in fact operate the relay, or not?

    If you connect the base directly to +5 volts (You can do that with an
    emitter follower), the voltage at the emitter and across the relay
    would be about 4.35 volts. If you do use a base resistor with that
    for spike protection (in case the transistor shorts out), make it no
    more than 100 or 200 ohms.

    You don't need the 100 ohm resistor in the collector either, although
    with a 12 volt supply, the 100 ohms won't make an difference.

    Here is another thing I didn't understand.

    >I assumed this mean't the circuit would work with the bs/2's output levels,
    >and put the thing together on a board, but DING, it didn't. The bs/2's
    >output level of 3.8V just isn't enough to trigger the transistor.


    If that is the voltage you measured on the Stamp pin, that means the
    Stamp is loaded down. The Stamp BS2 pins have a small signal output
    resistance of about 80 ohms. With 0.62 mA through that, the drop
    would only be 50 millivolts, and you should see about 4.95 volts at
    the base of the transistor. (Assuming you connect the base right to
    the pin--no 1500 ohms.) Take away another 0.6 volts for the
    base-emitter drop, and you have 4.3 volts across the relay. That
    should operate it fine.

    Measure again. It should work! The LED worked, right, although
    driving an LED directly from an emitter follower without a series
    resistor is not a good idea. (excess current).

    Another possibility is that the relay turn-on current is resetting
    your Stamp, and the 3.8 volts you are seeing on the Stamp pin is an
    artifact of a Stamp in distress. This is a common problem. Try more
    filtering on the power supply or right by the relay.

    -- best regards
    Tracy Allen
    electronically monitored ecosystems
    http://www.emesystems.com
    mailto:tracy@e...





    >Okay, folks, I need advice from someone smarter than me, which shouldn't be
    >too difficult here. ;-) I'm a bit rusty with transistors, and I'm having
    >problems setting up one to act as a switch.
    >
    > * I have an NPN transistor with a 100ohm resistor from the collector to
    >+12.
    > * The emitter is connected to ground via a relay coil (70ohm
    >dc resistance,
    >75ma operating current).
    > * The coil has the appropriate transient protection diode.
    > * The base is has a 1.5k resistor which connects it to the stamp.
    >
    >When the base is connected, via the resistor, directly to the 5v rail, it
    >turns the relay on and off as it should. I measured the base current at
    >around 620uA, and the base voltage was 5v.
    >
    >I assumed this mean't the circuit would work with the bs/2's output levels,
    >and put the thing together on a board, but DING, it didn't. The bs/2's
    >output level of 3.8V just isn't enough to trigger the transistor.
    >
    >I tried bypassing the 1.5k resistor, hoping an increased base current would
    >turn on the transistor, but nada.
    >
    >I tried replacing the relay with an LED just to see if the transistor would
    >switch properly, and it did. The LED turns on and off with the stamp's
    >output level, but when I replaced it with the relay, nothing.
    >
    >I measured the 3.8v at the base when the stamp was trying to drive it.
    >
    >What the heck am I missing here? I though the thing would switch as soon as
    >the base voltage was about .6-.7 volts above the emitter. Is there some
    >minimum base current to collector current relationship I need to know about?
    >
    >I know I could probably bypass the whole problem by simply driving the relay
    >with 5 volts, but now that the circuit is built (I didn't actually test
    >using the bs/2's output, I only connected the base of the transistor
    >directly to the 5volt rail, and, when that worked, assumed it would work
    >with the bs/2), I'd like to know what I'm missing. It seems like it should
    >work.
    >
    >thanks,
    >
    >
    >d..
    >
    >**************************************************************************
    >* David Okagaki dokagaki@w...
    >*
    >* "The light at the end of the tunnel is that of the on coming train!"
    >*
    >**************************************************************************
    >
    >
    >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.
    >
    >
    >Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
  • ArchiverArchiver Posts: 46,084
    edited 2003-06-19 03:01
    In a message dated 6/18/2003 5:42:55 PM Pacific Daylight Time,
    tracy@e... writes:

    > You have this transistor wired in a good configuration, called
    > "emitter follower". It is a perfectly good circuit to drive a relay
    > coil that would operate okay with 4--5 volts across it. The emitter
    > follower, when appropriate, is the simplest possible current and
    > power amplifier, and it is also very fast acting.

    Perfectly good configuration as long at the load on the emitter (relay coil
    in this case) can be activated by a voltage that is a diode drop less that what
    voltage you put on the base.

    Therefore if you put 3.8 volts on the base, the emitter will be approximately
    3.1 volts.....is 3.1 volts enough to turn on your relay.....?


    [noparse][[/noparse]Non-text portions of this message have been removed]
  • ArchiverArchiver Posts: 46,084
    edited 2003-06-19 13:42
    check out this web site for schematics showing how to configure transistors
    to switch relays, lamps, LED's, solenoids, valves, dc motors, etc. with
    basic stamps.
    Jim
    http://www.geocities.com/jimforkin2003/


    Original Message
    From: Dave [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=iXDtrYjstto82ln5NEGNX3-spXMMZx9U1H1eUPm0jGFbRpG_MWh34MX2vd4KALV9wdH-grBJlZ7CQGjncp1O8Q]dokagaki@w...[/url
    Sent: Wednesday, June 18, 2003 6:38 PM
    To: basicstamps@yahoogroups.com
    Subject: [noparse][[/noparse]basicstamps] transistor switching question


    Okay, folks, I need advice from someone smarter than me, which shouldn't be
    too difficult here. ;-) I'm a bit rusty with transistors, and I'm having
    problems setting up one to act as a switch.

    * I have an NPN transistor with a 100ohm resistor from the collector to
    +12.
    * The emitter is connected to ground via a relay coil (70ohm dc resistance,
    75ma operating current).
    * The coil has the appropriate transient protection diode.
    * The base is has a 1.5k resistor which connects it to the stamp.

    When the base is connected, via the resistor, directly to the 5v rail, it
    turns the relay on and off as it should. I measured the base current at
    around 620uA, and the base voltage was 5v.

    I assumed this mean't the circuit would work with the bs/2's output levels,
    and put the thing together on a board, but DING, it didn't. The bs/2's
    output level of 3.8V just isn't enough to trigger the transistor.

    I tried bypassing the 1.5k resistor, hoping an increased base current would
    turn on the transistor, but nada.

    I tried replacing the relay with an LED just to see if the transistor would
    switch properly, and it did. The LED turns on and off with the stamp's
    output level, but when I replaced it with the relay, nothing.

    I measured the 3.8v at the base when the stamp was trying to drive it.

    What the heck am I missing here? I though the thing would switch as soon as
    the base voltage was about .6-.7 volts above the emitter. Is there some
    minimum base current to collector current relationship I need to know about?

    I know I could probably bypass the whole problem by simply driving the relay
    with 5 volts, but now that the circuit is built (I didn't actually test
    using the bs/2's output, I only connected the base of the transistor
    directly to the 5volt rail, and, when that worked, assumed it would work
    with the bs/2), I'd like to know what I'm missing. It seems like it should
    work.

    thanks,


    d..

    **************************************************************************
    * David Okagaki dokagaki@w...
    *
    * "The light at the end of the tunnel is that of the on coming train!"
    *
    **************************************************************************


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  • ArchiverArchiver Posts: 46,084
    edited 2003-06-19 17:16
    thanks to everyone for the great responses. I just rewired the circuit by
    connecting the emitter directly to ground, and the collector to +12 through
    the relay coil and the 100ohm resistor (I put the resistor in because it's a
    5volt coil). Works great; I guess I didn't really understand the workings
    of the Vbe voltage because I didn't even think about the voltage drop of the
    coil in the original configuration, and the fact that it needed to be
    figured into the required Vbase trigger voltage.

    Thanks again, everyone.


    d...

    >
    Original Message
    > From: smartdim@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=F09HVTXAmBFhCUDG2N3BOyyiWI0b8wUEBtpU8kyl3ApCzcfzIvdv4n0-d-Ct5V8JPKgqy0MErw]smartdim@a...[/url
    > Sent: Wednesday, June 18, 2003 4:30 PM
    > To: basicstamps@yahoogroups.com
    > Subject: Re: [noparse][[/noparse]basicstamps] transistor switching question
    >
    >
    > In a message dated 6/18/2003 3:40:42 PM Pacific Daylight Time,
    > dokagaki@w... writes:
    >
    > > Okay, folks, I need advice from someone smarter than me, which
    > shouldn't be
    > > too difficult here. ;-) I'm a bit rusty with transistors, and
    > I'm having
    > > problems setting up one to act as a switch.
    > >
    > > * I have an NPN transistor with a 100ohm resistor from the
    > collector to
    > > +12.
    > > * The emitter is connected to ground via a relay coil (70ohm dc
    > > resistance,
    > > 75ma operating current).
    > > * The coil has the appropriate transient protection diode.
    > > * The base is has a 1.5k resistor which connects it to the stamp.
    > >
    > > When the base is connected, via the resistor, directly to the
    > 5v rail, it
    > > turns the relay on and off as it should. I measured the base current at
    > > around 620uA, and the base voltage was 5v.
    > >
    > > I assumed this mean't the circuit would work with the bs/2's
    > output levels,
    > > and put the thing together on a board, but DING, it didn't. The bs/2's
    > > output level of 3.8V just isn't enough to trigger the transistor.
    > >
    > > I tried bypassing the 1.5k resistor, hoping an increased base
    > current would
    > > turn on the transistor, but nada.
    > >
    > > I tried replacing the relay with an LED just to see if the
    > transistor would
    > > switch properly, and it did. The LED turns on and off with the stamp's
    > > output level, but when I replaced it with the relay, nothing.
    > >
    > > I measured the 3.8v at the base when the stamp was trying to drive it.
    > >
    > > What the heck am I missing here? I though the thing would
    > switch as soon as
    > > the base voltage was about .6-.7 volts above the emitter. Is there some
    > > minimum base current to collector current relationship I need
    > to know about?
    > >
    > > I know I could probably bypass the whole problem by simply
    > driving the relay
    > > with 5 volts, but now that the circuit is built (I didn't actually test
    > > using the bs/2's output, I only connected the base of the transistor
    > > directly to the 5volt rail, and, when that worked, assumed it would work
    > > with the bs/2), I'd like to know what I'm missing. It seems
    > like it should
    > > work.
    > >
    > > thanks,
    > >
    > >
    > > d..
    > >
    >
    > d,
    >
    > what is the transistor? 2n3904? or....
    > From what I read in your post, the transistor should
    > saturate....assuming the
    > transistor has a Beta of 100 or more...
    >
    > Stamp output 3.8 minus Vbe of 0.7v leaves you with about 3v
    > across 1.5k ohms
    > which will give you 2 ma of "base drive" current. Multiply this 2
    > ma times
    > beta (100) and you should be capable of 200ma of collector
    > current which is more
    > that what is need to drive your relay....
    >
    > But.....I would wire this differently........because the base
    > voltage must be
    > capable of being 0.7 volts more than it takes to turn the relay on....3.8
    > from the stamp may not be high enough...
    >
    > Rewire as follows with a 2n3904 (almost guaranteed to work)
    >
    > Not sure why you have the 100 ohm resistor in the circuit.....
    >
    > Connect the relay coil to +12 volts and the other end of the
    > relay coil to
    > the collector. Connect emitter directly to ground....Make the NPN provide
    > GROUND for your relay, NOT provide power, which is what your
    > current configuration
    > is trying to do......
    >
    > Write back with results
    >
    >
    > [noparse][[/noparse]Non-text portions of this message have been removed]
    >
    >
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  • ArchiverArchiver Posts: 46,084
    edited 2003-06-19 17:26
    In a message dated 6/19/2003 9:16:43 AM Pacific Daylight Time,
    dokagaki@w... writes:

    >
    > Thanks again, everyone.

    You are welcome,,,,,glad to help


    [noparse][[/noparse]Non-text portions of this message have been removed]
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