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NEWBIE input question. — Parallax Forums

NEWBIE input question.

ArchiverArchiver Posts: 46,084
edited 2001-09-09 05:31 in General Discussion
As I've mentioned before, I'm pretty new to stamps, so no laughing [noparse]:)[/noparse]


I'm trying to use pin1 as in input, with a switch and a 10k
resistor.

The problem I am having is that when the switch is 'open' the state
of the pin changes from 0 to 1 aparently randomly. (even the book
said it would) And if the switch is closed, the state is ALWAYS 1.

So how can I check the state of the pin and trust what it says? It
doesnt seem to matter if I write a 0 to the pin 1st or not, if the
switch is open, the results are anyone's guess [noparse]:)[/noparse]

Thanks in advance,


John

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2001-09-08 19:25
    John,is the resister tied to gnd or 5v?
    the resister should be opposite of switch.
    so when switch is off the pin should read what ever the resister is tied to.
    when you press switch the pin changes state.
    when released the resister pulls pin the other way.
    hope this helps
    victor
    Original Message
    From: <john@l...>
    To: <basicstamps@yahoogroups.com>
    Sent: Saturday, September 08, 2001 2:19 PM
    Subject: [noparse][[/noparse]basicstamps] NEWBIE input question.


    > As I've mentioned before, I'm pretty new to stamps, so no laughing [noparse]:)[/noparse]
    >
    >
    > I'm trying to use pin1 as in input, with a switch and a 10k
    > resistor.
    >
    > The problem I am having is that when the switch is 'open' the state
    > of the pin changes from 0 to 1 aparently randomly. (even the book
    > said it would) And if the switch is closed, the state is ALWAYS 1.
    >
    > So how can I check the state of the pin and trust what it says? It
    > doesnt seem to matter if I write a 0 to the pin 1st or not, if the
    > switch is open, the results are anyone's guess [noparse]:)[/noparse]
    >
    > Thanks in advance,
    >
    >
    > John
    >
    >
    > 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 2001-09-08 19:28
    Thanks AL,

    I'll go give that a try.

    -John


    At 01:31 PM 9/8/01 -0500, Al Williams wrote:
    >This sounds like you don't have the resistor in the right place. Here's how
    >it usually works:
    >
    >Connect one end of the 10k resistor to +5V and the other end to the Stamp
    >pin. This is a PULL UP resistor. Now the Stamp will consistently read a "1".
    >Connect the switch from the pin to ground. When you push the switch you will
    >consistently read a "0". The purpose of the resistor is to prevent you from
    >short circuiting your power supply when you push the button. Without the
    >resistor you'd draw lots of current until something blew up. With the
    >resistor you will draw about 5/10K or about 500uA which is no big deal (the
    >Stamp input is essentially an open circuit).
    >
    >With the Stamp and certain other types of ICs you can reverse this to use a
    >pull down resistor if you like. However, with some logic families like TTL
    >pull up resistors make sense and pull down resistors don't. That's because
    >those logic families don't provide as much current at a 1 output as they do
    >with a 0 output.
    >
    >So not in the general case, but with the Stamp, you could connect the
    >resistor to ground and the switch to +5V and still be OK.
    >
    >Regards,
    >
    >Al Williams
    >AWC
    >* Connect your Stamp to the Internet
    >http://www.al-williams.com/awce/netporter.htm
    >
    >
    > >
    Original Message
    > > From: john@l... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=k0FVrXfo6xmxpJ77SfFDan9wXzY8XJXU1ngo7VlUb_kF6RP6XaZJQYTyhIg8BGc1k0ck75xu]john@l...[/url
    > > Sent: Saturday, September 08, 2001 1:20 PM
    > > To: basicstamps@yahoogroups.com
    > > Subject: [noparse][[/noparse]basicstamps] NEWBIE input question.
    > >
    > >
    > > As I've mentioned before, I'm pretty new to stamps, so no laughing [noparse]:)[/noparse]
    > >
    > >
    > > I'm trying to use pin1 as in input, with a switch and a 10k
    > > resistor.
    > >
    > > The problem I am having is that when the switch is 'open' the state
    > > of the pin changes from 0 to 1 aparently randomly. (even the book
    > > said it would) And if the switch is closed, the state is ALWAYS 1.
    > >
    > > So how can I check the state of the pin and trust what it says? It
    > > doesnt seem to matter if I write a 0 to the pin 1st or not, if the
    > > switch is open, the results are anyone's guess [noparse]:)[/noparse]
    > >
    > > Thanks in advance,
    > >
    > >
    > > John
    > >
    > >
    > > 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/
    > >
    >
    >
    >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 2001-09-08 19:31
    This sounds like you don't have the resistor in the right place. Here's how
    it usually works:

    Connect one end of the 10k resistor to +5V and the other end to the Stamp
    pin. This is a PULL UP resistor. Now the Stamp will consistently read a "1".
    Connect the switch from the pin to ground. When you push the switch you will
    consistently read a "0". The purpose of the resistor is to prevent you from
    short circuiting your power supply when you push the button. Without the
    resistor you'd draw lots of current until something blew up. With the
    resistor you will draw about 5/10K or about 500uA which is no big deal (the
    Stamp input is essentially an open circuit).

    With the Stamp and certain other types of ICs you can reverse this to use a
    pull down resistor if you like. However, with some logic families like TTL
    pull up resistors make sense and pull down resistors don't. That's because
    those logic families don't provide as much current at a 1 output as they do
    with a 0 output.

    So not in the general case, but with the Stamp, you could connect the
    resistor to ground and the switch to +5V and still be OK.

    Regards,

    Al Williams
    AWC
    * Connect your Stamp to the Internet
    http://www.al-williams.com/awce/netporter.htm


    >
    Original Message
    > From: john@l... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=zOvtzFPSnNpL51eFHd0FVSKpxcZ4GBp3UetNRMgD5-O2hXOrvFupxQPzi9QZ-zLw_BVLvbWVv2jH]john@l...[/url
    > Sent: Saturday, September 08, 2001 1:20 PM
    > To: basicstamps@yahoogroups.com
    > Subject: [noparse][[/noparse]basicstamps] NEWBIE input question.
    >
    >
    > As I've mentioned before, I'm pretty new to stamps, so no laughing [noparse]:)[/noparse]
    >
    >
    > I'm trying to use pin1 as in input, with a switch and a 10k
    > resistor.
    >
    > The problem I am having is that when the switch is 'open' the state
    > of the pin changes from 0 to 1 aparently randomly. (even the book
    > said it would) And if the switch is closed, the state is ALWAYS 1.
    >
    > So how can I check the state of the pin and trust what it says? It
    > doesnt seem to matter if I write a 0 to the pin 1st or not, if the
    > switch is open, the results are anyone's guess [noparse]:)[/noparse]
    >
    > Thanks in advance,
    >
    >
    > John
    >
    >
    > 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 2001-09-08 23:39
    Don't you also want a weak pulldown resistor in the event the Stamp pin gets
    switched to an output and is set high? This is what's mentioned in some of
    the articles I have been reading, as well as the switch circuit on the
    Activity Board, if I remember right.
    Original Message

    > This sounds like you don't have the resistor in the right place. Here's
    how
    > it usually works:
    >
    > Connect one end of the 10k resistor to +5V and the other end to the Stamp
    > pin. This is a PULL UP resistor. Now the Stamp will consistently read a
    "1".
    > Connect the switch from the pin to ground. When you push the switch you
    will
    > consistently read a "0". The purpose of the resistor is to prevent you
    from
    > short circuiting your power supply when you push the button. Without the
    > resistor you'd draw lots of current until something blew up. With the
    > resistor you will draw about 5/10K or about 500uA which is no big deal
    (the
    > Stamp input is essentially an open circuit).
    >
    > With the Stamp and certain other types of ICs you can reverse this to use
    a
    > pull down resistor if you like. However, with some logic families like TTL
    > pull up resistors make sense and pull down resistors don't. That's because
    > those logic families don't provide as much current at a 1 output as they
    do
    > with a 0 output.
    >
    > So not in the general case, but with the Stamp, you could connect the
    > resistor to ground and the switch to +5V and still be OK.
  • ArchiverArchiver Posts: 46,084
    edited 2001-09-08 23:44
    If the Stamp pin goes to an output, there is a danger that if you pushed the
    button and held it you could damage the Stamp output (high output, short
    circuit to ground). The cure for this is not a pull up/down, but a small
    series resistor between the pin and the switch. A 1K resistor, for example
    would limit the current to 5mA.

    Al Williams
    AWC
    * Floating point A/D
    http://www.al-williams.com/awce/pak9.htm

    >
    Original Message
    > From: Rodent [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=H5Ao8s5hjjJMnFLpIZGG3_9rgvMxJwbTKkJrWqtu85NoEHSt4nOTA73JSc3MYZiTOsCqyeQnBRBnYA]daweasel@s...[/url
    > Sent: Saturday, September 08, 2001 5:39 PM
    > To: basicstamps@yahoogroups.com
    > Subject: Re: [noparse][[/noparse]basicstamps] NEWBIE input question.
    >
    >
    > Don't you also want a weak pulldown resistor in the event the
    > Stamp pin gets
    > switched to an output and is set high? This is what's mentioned in some of
    > the articles I have been reading, as well as the switch circuit on the
    > Activity Board, if I remember right.
    >
    >
    Original Message
    >
    > > This sounds like you don't have the resistor in the right place. Here's
    > how
    > > it usually works:
    > >
    > > Connect one end of the 10k resistor to +5V and the other end to
    > the Stamp
    > > pin. This is a PULL UP resistor. Now the Stamp will consistently read a
    > "1".
    > > Connect the switch from the pin to ground. When you push the switch you
    > will
    > > consistently read a "0". The purpose of the resistor is to prevent you
    > from
    > > short circuiting your power supply when you push the button. Without the
    > > resistor you'd draw lots of current until something blew up. With the
    > > resistor you will draw about 5/10K or about 500uA which is no big deal
    > (the
    > > Stamp input is essentially an open circuit).
    > >
    > > With the Stamp and certain other types of ICs you can reverse
    > this to use
    > a
    > > pull down resistor if you like. However, with some logic
    > families like TTL
    > > pull up resistors make sense and pull down resistors don't.
    > That's because
    > > those logic families don't provide as much current at a 1 output as they
    > do
    > > with a 0 output.
    > >
    > > So not in the general case, but with the Stamp, you could connect the
    > > resistor to ground and the switch to +5V and still be OK.
    >
    >
    >
    >
    > 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 2001-09-09 05:31
    Thanks everyone... you solved my problem. I DID have it wired wrong. Not
    only am I new to stamps, I'm new to electronics!

    Some day I'll know enough to help some too ! [noparse]:)[/noparse]


    Thanks again,


    John




    At 02:25 PM 9/8/01 -0400, victor Faria wrote:
    >John,is the resister tied to gnd or 5v?
    *snip*snip*
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