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Sensing two switch contacts with one digital I/O on 932
This thread was started in the I/O Forum by user phwhite on 24-6-2004 21:06
To add a posting to this thread, click on the message you wish to reply to. Your reply will be inserted at that point in the thread.
Topic Posted User
*Sensing two switch contacts with one digital I/O on 932
I have a job where I/O is pretty tight - I have two clean contact switches to detect and only one I/O left on the chip. Anyone have any ideas about how to do this, or even if it''s possible?
Reply to this post
24-6-2004 21:06
Views: 1870
phwhite
RE: Sensing two switch contacts with one digital I/O on 932
Hi
I''ve not tried this, but it may work!
The basic idea is to put a different value resistor in series with each switch from 3V, with the resistors feeding a single capacitor. The I/O pin connects to the RC junction through another resistor RL. Other end of the cap connects to 0V.

To determine if a switch is closed, set the I/O pin to 0V to first discharge the cap. Then set the pin as an input. If either switch is closed, the cap will charge through the associated resistor. The micro should time how long it
... more (see whole posting)
Reply to this post
14-7-2004  4:15
Views: 1902
steveglover
*RE: Sensing two switch contacts with one digital I/O on 932
I had thought of something like that but wanted a scheme that could determine the state of the pin with just one visit, rather than checking it again after a delay.

On the other hand, if the RC time constant was small enough you wouldn''t need to wait that long anyway.

Thanks for the comments.
Reply to this post
25-7-2004  2:20
Views: 1865
phwhite
RE: Sensing two switch contacts with one digital I/O on 932
HI!
Here is a idea non tested, to connect 2 switches on a single LPC932 port without timer.
HARDWARE SHEMATIC:
Connect the switch SW1 between the port and 0V .
Connect the other switch SW2 in series with R1=1Kohm between the port and +3V.
Connect a resistor R2 (2.2Mohm) between the port and 0V.
SOFTWARE:
1)The software put the port in input-only mode.
If the state of the port is 1 (level=+3V) then the switch SW2 is ON.
2)Folowing, The software put the port in quasi-bidirectional mode.
If the state of the port is 0 (level=0V) then the switch
... more (see whole posting)
Reply to this post
17-9-2004 14:35
Views: 1862
pcayarcy
RE: Sensing two switch contacts with one digital I/O on 932
switch to a 935. You can than use the ADC to read as much as 12 switches on 1 I/O pin by using a voltagedivider network. I have done this often and is does work realy fine. 932 and 935 are pincompatible and the difference in price is nearly nothing.
succes

BEst regards

Robert
Reply to this post
15-8-2006 12:50
Views: 1267
RobertUD
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