What chip? Inputs and rs232

[peetcool9]

hello, i am trying to get something to read as many "switches" as posible. i was trying to use the parrallel port on a computer but that can only carry 5 inputs. is there a chip that can read just an on or off state on many pins? what would be another soution? i would just like it to serialy send status of all the pins to the comp to be decoded with software. i can handle the software stuff but the chip i am not sure what o use for this as there are soo many of them.
for now we can forget the fact that the chip has to be programmed. :wink:

thanks for the time. patrick

 

[Nigel Goodwin]

hello, i am trying to get something to read as many "switches" as posible. i was trying to use the parrallel port on a computer but that can only carry 5 inputs. is there a chip that can read just an on or off state on many pins? what would be another soution? i would just like it to serialy send status of all the pins to the comp to be decoded with software. i can handle the software stuff but the chip i am not sure what o use for this as there are soo many of them.
for now we can forget the fact that the chip has to be programmed. :wink:

thanks for the time. patrick

You could always be it in hardware, but it's probably a lot easier to do it in software with a micro-controller. Personally I would use one of the PIC range, but that's because I use PIC's, and micro-controller would do.

How many switches do you need?, using an 18 pin 16F628, and using one of the pins for the RS232 output, you have 15 I/O pins free - so you could have 15 switches (using one per pin) or multiplex them and have 56 switches.

 

[ivancho]

You could use a Octal transiver Tri-state like the 74HC245.

Using the outputs of the parallel port, you can connect a whole bunch of this 74HC245 and control their enable line so that only one of them is enable at a time..... and you can ground the direction pin and read the outputs as you enable the lines.

Just another idea instead of the serial... although I would probably go serial for simplicity, efficiency and size :wink:

Ivancho

 

[panic mode]

When ever you need to controll a LOT of something, (switches, LEDs,...)
it's time to multiplex. For example to use 9 switches, sure you could use
9 inputs but if you multiplex them, you could use 3 outputs and 3 inputs
(3x3=9). You could also use 9 outputs and 1 input (9x1=9).
LPTs are not all the same but even so you should have couple of output
and input lines (8x5?). Do you think this is plenty?

 

[TheAnimus]

If your parport supports the 'newer' modes of data transfer, you should be able to have 13 inputs (without plexing).