Need Help With PC Hardware Interface Project.

[[email protected]]

I've had an idea for a PC hardware interface rolling around in my head
for a while, but after doing some inital investigation on the web, I
have not found anything that has helped me get started yet.

It basically goes like this...

I have a series of 256 momentary switches. I need to wire these
switches somehow, and interface them with a standard off-the-shelf PC
(Parallel interface???), and produce an 8-bit number from 0 to 255
(depending on which switch is pressed). This number should be something
that I could pick up using VB)

So, my questions are...

1. Is this even possible?
2. Is there a ready made device that an do this?
3. Are there plans for a device that can do something similar to this?

Thanks!
ferrell

 

[Frithiof Andreas Jensen]

I've had an idea for a PC hardware interface rolling around in my head
for a while, but after doing some inital investigation on the web, I
have not found anything that has helped me get started yet.

It basically goes like this...

I have a series of 256 momentary switches. I need to wire these
switches somehow,

Make you mind up!

and interface them with a standard off-the-shelf PC
(Parallel interface???), and produce an 8-bit number from 0 to 255
(depending on which switch is pressed). This number should be something
that I could pick up using VB)

So, my questions are...

1. Is this even possible?
yes.

2. Is there a ready made device that an do this?

Keyboard ("I need to wire these switches somehow," ) or Analogue to Digital
Converter ("I have a series of 256 momentary switches") connect different
resistors in parallel with each switch, measure current.

3. Are there plans for a device that can do something similar to this?

Probably, once you decide what "this" is!

 

[PeteS]

I've had an idea for a PC hardware interface rolling around in my head
for a while, but after doing some inital investigation on the web, I
have not found anything that has helped me get started yet.

It basically goes like this...

I have a series of 256 momentary switches. I need to wire these
switches somehow, and interface them with a standard off-the-shelf PC
(Parallel interface???), and produce an 8-bit number from 0 to 255
(depending on which switch is pressed). This number should be something
that I could pick up using VB)

So, my questions are...

1. Is this even possible?

Sure. There's a number of ways. I would go for a row-column encoder (16
x 16) with a simple controller that can also do priority encoding (see
below)

2. Is there a ready made device that an do this? Probably
3. Are there plans for a device that can do something similar to this?

It's not that difficult to do in the first place.

One of the issues you will face is - what happens if more than one
switch is pressed? What should the system do? There are 4 choices:

a. Report all closed switches
b. Suppress all reports if more than one switch pressed
c. Report the 'highest' pressed switch
d. Report the lowest pressed switch

b,c and d are trivial to implement. a is harder, but eminently do-able.

Interfacing to a standard PC can be done in a number of ways. The
easiest for me would be to use a serial port and some predefined data
protocol. I am sure VB can do that (although I have avoided it like the
plague, a boss of mine insisted it be used, so I wrote C backend DLLs
for it instead).

If you do that, your circuit will need a RS232 level converter (you
could even get the power to drive your circuit from the port if you
don't need very much).

Thanks!
ferrell

You're welcome

Cheers

PeteS

 

[Rich Grise]

I've had an idea for a PC hardware interface rolling around in my head
for a while, but after doing some inital investigation on the web, I
have not found anything that has helped me get started yet.

It basically goes like this...

I have a series of 256 momentary switches. I need to wire these
switches somehow, and interface them with a standard off-the-shelf PC
(Parallel interface???), and produce an 8-bit number from 0 to 255
(depending on which switch is pressed). This number should be something
that I could pick up using VB)

So, my questions are...

1. Is this even possible?
2. Is there a ready made device that an do this?
3. Are there plans for a device that can do something similar to this?

Thanks!
ferrell

I've been avoiding this question, because it really belongs in .basics.
In fact, I've crossposted this reply.

Learn how to use the parallel port, and then just make one 8-bit output
port, one 8-bit input port, and put the switches in a crosspoint matrix.

Wait a minute, that's only 64. OK, 16 bits of output, and 16 bits of input.

That's still not hard.

Nobody's going to do that homework for you, but you can get hundreds
of google hits on stuff like "parallel port interfacing" and such.

There are so many ways to do this, it'd take all day to describe them.
a couple of 74x138 and one ea. 74x154 could do it, with a little software
smarts.

Good Luck!
Rich

 

[Bob Masta]

I've been avoiding this question, because it really belongs in .basics.
In fact, I've crossposted this reply.

Learn how to use the parallel port, and then just make one 8-bit output
port, one 8-bit input port, and put the switches in a crosspoint matrix.

Wait a minute, that's only 64. OK, 16 bits of output, and 16 bits of input.

That's still not hard.

Nobody's going to do that homework for you, but you can get hundreds
of google hits on stuff like "parallel port interfacing" and such.

There are so many ways to do this, it'd take all day to describe them.
a couple of 74x138 and one ea. 74x154 could do it, with a little software
smarts.

Good Luck!
Rich

Also, just remember that with newer versions of Windows
(NT, XP, 2K), you no longer have direct access to the parallel port
unless you run a special ring 0 driver like GiveIO. Not needed
with Win9x or earlier.

Best regards,




Bob Masta
dqatechATdaqartaDOTcom

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