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PICList Thread
'Out of I/O Lines'
1998\04\02@083051 by Ed Arnold

I am working on a project which uses all of the i/o pins on a 16F84.
But I want to add some user indicators to show when operations are being
carried out.  I chose some momentary switches with internal lamps.  I
have already done the math with these lamps and I think it's safe to use
a standard 2N2222 setup.  My problem lies with available I/O lines.  I
have none.  I want to use the same I/O line that the switch is connected
to, since it will not be needed during this time frame.  But I am not
sure if this will work.  I have an idea of what the schematic *might*
should look like, but I am not sure.  I really don't wish to smoke
anything.  Can anyone lend me a hand with schematic ideas an even some
code examples.

Ed Arnold

1998\04\02@103036 by Hardy e/ou Rafael Pinto

   Take a look at PIC Application notes, AN557 - Four Channel Digital
Voltmeter with Display and Keyboard. They show how to multiplex inputs and
outputs out of a 16C71, but I guess you can use some ideas from there.

   Rafael Pinto

{Original Message removed}

1998\04\02@123849 by Michael Hagberg

good relay / lamp drivers are available from i
think the part number i use is 5832 uses  clock, data, and latch lines to
pic and this device has 32 outputs, there are also versions the are 8


{Original Message removed}

1998\04\03@035837 by Caisson

{Quote hidden}

Try this :

From Vcc to Gnd : Led, Resistor, T-Junction to Pic, Switch.
Put a resistor from Vcc to the T-Junction as a Pull-Up.

The PIC I/O-line is programmed as a Open-Collector output (Set I/O
to Zero & fiddle around with the Tri-state (tris) register).
To switch the LED ON : Set the I/O-line to output, thus shorting the
To switch the LED OFF : Put the I/O-line to Tri-state.
To read your switch :  Put the I/O-line to Tri-state & read the

Draw-Back : You have to switch your LED off to read your button, and the
will be ON if you press the button.

 Rudy Wieser

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