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Newbie BS2 user w/ Newbie Question — Parallax Forums

Newbie BS2 user w/ Newbie Question

ArchiverArchiver Posts: 46,084
edited 2001-12-25 02:35 in General Discussion
I just hooked up my BS2 for the first time, and tested it by
connecting this simple circuit (the cimplest one I could find) from
the manual:

+5v
LED
220 Ohm Res.
I/O Pin 0

The circuit works, and I am really excited about getting into
STAMPs. What I don't get is, why is the 220 Ohm resistor there? I
also connected the circuit without it, and it still works just as
well. The voltage across the LED w/o the resistor is 5v, and with it
is 3.7v. Is the sole purpose of the resistor to lower the voltage a
little, dimming the LED a little? Or does it serve some other
purpose?

Thanks in advance. Any info on good online resources would be
appreciated.

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2001-12-24 16:18
    Here's two articles to read:
    http://www.al-williams.com/wd5gnr/stampfaq.htm#s2.4

    http://www.al-williams.com/wd5gnr/basiccir.htm

    Al Williams
    AWC
    * NEW KIT: Need a 5V Power Supply?
    http://www.al-williams.com/awce/ps1.htm



    >
    Original Message
    > From: apecitydotcom [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=PMWsAotT7aXbEsyM-Ji_wtduWgPHglcgB59buUlYxd21CoBg4y4u7if4OSKp_HdPhsPKvTBitFD65Ve8aQ]fines@m...[/url
    > Sent: Monday, December 24, 2001 10:06 AM
    > To: basicstamps@yahoogroups.com
    > Subject: [noparse][[/noparse]basicstamps] Newbie BS2 user w/ Newbie Question
    >
    >
    > I just hooked up my BS2 for the first time, and tested it by
    > connecting this simple circuit (the cimplest one I could find) from
    > the manual:
    >
    > +5v
    LED
    220 Ohm Res.
    I/O Pin 0
    >
    > The circuit works, and I am really excited about getting into
    > STAMPs. What I don't get is, why is the 220 Ohm resistor there? I
    > also connected the circuit without it, and it still works just as
    > well. The voltage across the LED w/o the resistor is 5v, and with it
    > is 3.7v. Is the sole purpose of the resistor to lower the voltage a
    > little, dimming the LED a little? Or does it serve some other
    > purpose?
    >
    > Thanks in advance. Any info on good online resources would be
    > appreciated.
    >
    >
    > 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 2001-12-24 16:22
    The resistor is there to control the current through the LED circuit. This
    protects the LED and the Stamp. As you get more involved in electronics,
    you'll learn to calculate proper resistor values for your unique circuits.

    LEDs have a specified forward voltage that is usually in the range of 1.2 to
    1.7 volts. The resistor, if you will, soaks up the rest (since the circuit
    voltage is 5 volts). Lets say, for example that your LED had a forward
    voltage of 1.4 volts (very typical). That would leave 3.6 volts across the
    resistor. Using Ohm's Law, we can determine that the current flow through
    the circuit is about 16 milliamps.

    Since you can't light too many LEDs at 16 mA, you might consider changing
    your resistor value to 470 ohms or 1 kOhm. That will let the Stamp light
    more at the same time.

    You might consider Scott Edwards' book "Programming And Customizing The BASIC
    Stamp Microcontroller." It will help you get started in Stamps and give you
    some fundamentals in electronics as well.

    -- Jon Williams
    -- Parallax


    In a message dated 12/24/01 10:06:32 AM Central Standard Time,
    fines@m... writes:


    > I just hooked up my BS2 for the first time, and tested it by
    > connecting this simple circuit (the cimplest one I could find) from
    > the manual:
    >
    > +5v
    LED
    220 Ohm Res.
    I/O Pin 0
    >
    > The circuit works, and I am really excited about getting into
    > STAMPs. What I don't get is, why is the 220 Ohm resistor there? I
    > also connected the circuit without it, and it still works just as
    > well. The voltage across the LED w/o the resistor is 5v, and with it
    > is 3.7v. Is the sole purpose of the resistor to lower the voltage a
    > little, dimming the LED a little? Or does it serve some other
    > purpose?
    >
    > Thanks in advance. Any info on good online resources would be
    >




    [noparse][[/noparse]Non-text portions of this message have been removed]
  • ArchiverArchiver Posts: 46,084
    edited 2001-12-24 16:51
    The resistor is there to drop the voltage to the level required by the LED.
    Typically LED's require 1.7 to 2.1 volts to operate and any higher voltage
    will cause it to burn out. It sounds like you lucked out not smoking the LED
    or Stamp. In the future I would follow the directions so won't damage
    anything.

    As far as the resistor value, knowing how much power the LED consumes and
    what voltage it requires, along with a simple formula allows you to
    determine what resistor to use.
    Original Message

    > I just hooked up my BS2 for the first time, and tested it by
    > connecting this simple circuit (the cimplest one I could find) from
    > the manual:
    >
    > +5v
    LED
    220 Ohm Res.
    I/O Pin 0
    >
    > The circuit works, and I am really excited about getting into
    > STAMPs. What I don't get is, why is the 220 Ohm resistor there? I
    > also connected the circuit without it, and it still works just as
    > well. The voltage across the LED w/o the resistor is 5v, and with it
    > is 3.7v. Is the sole purpose of the resistor to lower the voltage a
    > little, dimming the LED a little? Or does it serve some other
    > purpose?
  • ArchiverArchiver Posts: 46,084
    edited 2001-12-24 18:58
    The 220 ohm resistor is to limit the current thru the LED. Without this
    resistor you exceed the power dissipation of the LED.
    Original Message
    From: "apecitydotcom" <fines@m...>
    To: <basicstamps@yahoogroups.com>
    Sent: Monday, December 24, 2001 8:05 AM
    Subject: [noparse][[/noparse]basicstamps] Newbie BS2 user w/ Newbie Question


    > I just hooked up my BS2 for the first time, and tested it by
    > connecting this simple circuit (the cimplest one I could find) from
    > the manual:
    >
    > +5v
    LED
    220 Ohm Res.
    I/O Pin 0
    >
    > The circuit works, and I am really excited about getting into
    > STAMPs. What I don't get is, why is the 220 Ohm resistor there? I
    > also connected the circuit without it, and it still works just as
    > well. The voltage across the LED w/o the resistor is 5v, and with it
    > is 3.7v. Is the sole purpose of the resistor to lower the voltage a
    > little, dimming the LED a little? Or does it serve some other
    > purpose?
    >
    > Thanks in advance. Any info on good online resources would be
    > appreciated.
    >
    >
    > 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 2001-12-24 20:44
    The 220 ohms resistor is to limit not only the current thru the LED
    (you can pump amps thru the LED for short perios of time) but what is
    more important the current out of the stamp, you could fried it.

    --- In basicstamps@y..., "Stephen H Chapman" <chapman@t...> wrote:
    > The 220 ohm resistor is to limit the current thru the LED. Without
    this
    > resistor you exceed the power dissipation of the LED.
    >
    Original Message
    > From: "apecitydotcom" <fines@m...>
    > To: <basicstamps@y...>
    > Sent: Monday, December 24, 2001 8:05 AM
    > Subject: [noparse][[/noparse]basicstamps] Newbie BS2 user w/ Newbie Question
    >
    >
    > > I just hooked up my BS2 for the first time, and tested it by
    > > connecting this simple circuit (the cimplest one I could find)
    from
    > > the manual:
    > >
    > > +5v
    LED
    220 Ohm Res.
    I/O Pin 0
    > >
    > > The circuit works, and I am really excited about getting into
    > > STAMPs. What I don't get is, why is the 220 Ohm resistor there?
    I
    > > also connected the circuit without it, and it still works just as
    > > well. The voltage across the LED w/o the resistor is 5v, and
    with it
    > > is 3.7v. Is the sole purpose of the resistor to lower the
    voltage a
    > > little, dimming the LED a little? Or does it serve some other
    > > purpose?
    > >
    > > Thanks in advance. Any info on good online resources would be
    > > appreciated.
    > >
    > >
    > > To UNSUBSCRIBE, just send mail to:
    > > basicstamps-unsubscribe@y...
    > > 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 2001-12-24 23:27
    In a series ckt the current in any one branch is the same amount of current
    flow in all other branches.
    Original Message
    From: "acatano2002" <acatano2002@y...>
    To: <basicstamps@yahoogroups.com>
    Sent: Monday, December 24, 2001 12:44 PM
    Subject: [noparse][[/noparse]basicstamps] Re: Newbie BS2 user w/ Newbie Question


    > The 220 ohms resistor is to limit not only the current thru the LED
    > (you can pump amps thru the LED for short perios of time) but what is
    > more important the current out of the stamp, you could fried it.
    >
    >
    > --- In basicstamps@y..., "Stephen H Chapman" <chapman@t...> wrote:
    > > The 220 ohm resistor is to limit the current thru the LED. Without
    > this
    > > resistor you exceed the power dissipation of the LED.
    > >
    Original Message
    > > From: "apecitydotcom" <fines@m...>
    > > To: <basicstamps@y...>
    > > Sent: Monday, December 24, 2001 8:05 AM
    > > Subject: [noparse][[/noparse]basicstamps] Newbie BS2 user w/ Newbie Question
    > >
    > >
    > > > I just hooked up my BS2 for the first time, and tested it by
    > > > connecting this simple circuit (the cimplest one I could find)
    > from
    > > > the manual:
    > > >
    > > > +5v
    LED
    220 Ohm Res.
    I/O Pin 0
    > > >
    > > > The circuit works, and I am really excited about getting into
    > > > STAMPs. What I don't get is, why is the 220 Ohm resistor there?
    > I
    > > > also connected the circuit without it, and it still works just as
    > > > well. The voltage across the LED w/o the resistor is 5v, and
    > with it
    > > > is 3.7v. Is the sole purpose of the resistor to lower the
    > voltage a
    > > > little, dimming the LED a little? Or does it serve some other
    > > > purpose?
    > > >
    > > > Thanks in advance. Any info on good online resources would be
    > > > appreciated.
    > > >
    > > >
    > > > To UNSUBSCRIBE, just send mail to:
    > > > basicstamps-unsubscribe@y...
    > > > 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/
    > > >
    > > >
    > > >
    >
    >
    > 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 2001-12-25 02:35
    I am sorry.
    My point is that the LED can take amps, the stamp does not.

    --- In basicstamps@y..., "Stephen H Chapman" <chapman@t...> wrote:
    > In a series ckt the current in any one branch is the same amount of
    current
    > flow in all other branches.
    >
    Original Message
    > From: "acatano2002" <acatano2002@y...>
    > To: <basicstamps@y...>
    > Sent: Monday, December 24, 2001 12:44 PM
    > Subject: [noparse][[/noparse]basicstamps] Re: Newbie BS2 user w/ Newbie Question
    >
    >
    > > The 220 ohms resistor is to limit not only the current thru the
    LED
    > > (you can pump amps thru the LED for short perios of time) but
    what is
    > > more important the current out of the stamp, you could fried it.
    > >
    > >
    > > --- In basicstamps@y..., "Stephen H Chapman" <chapman@t...> wrote:
    > > > The 220 ohm resistor is to limit the current thru the LED.
    Without
    > > this
    > > > resistor you exceed the power dissipation of the LED.
    > > >
    Original Message
    > > > From: "apecitydotcom" <fines@m...>
    > > > To: <basicstamps@y...>
    > > > Sent: Monday, December 24, 2001 8:05 AM
    > > > Subject: [noparse][[/noparse]basicstamps] Newbie BS2 user w/ Newbie Question
    > > >
    > > >
    > > > > I just hooked up my BS2 for the first time, and tested it by
    > > > > connecting this simple circuit (the cimplest one I could find)
    > > from
    > > > > the manual:
    > > > >
    > > > > +5v
    LED
    220 Ohm Res.
    I/O Pin 0
    > > > >
    > > > > The circuit works, and I am really excited about getting into
    > > > > STAMPs. What I don't get is, why is the 220 Ohm resistor
    there?
    > > I
    > > > > also connected the circuit without it, and it still works
    just as
    > > > > well. The voltage across the LED w/o the resistor is 5v, and
    > > with it
    > > > > is 3.7v. Is the sole purpose of the resistor to lower the
    > > voltage a
    > > > > little, dimming the LED a little? Or does it serve some other
    > > > > purpose?
    > > > >
    > > > > Thanks in advance. Any info on good online resources would be
    > > > > appreciated.
    > > > >
    > > > >
    > > > > To UNSUBSCRIBE, just send mail to:
    > > > > basicstamps-unsubscribe@y...
    > > > > 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/
    > > > >
    > > > >
    > > > >
    > >
    > >
    > > To UNSUBSCRIBE, just send mail to:
    > > basicstamps-unsubscribe@y...
    > > 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/
    > >
    > >
    > >
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