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From: Rowan Sylvester-Bradley on 18 Jan 2010 07:02
I have to create a test harness to allow automatic testing of a system that
I'm working on. It needs several hundred digital inputs and several hundred
digital outputs. They don't need to be isolated or anything - just logic
input/outputs. I don't mind much what it looks like or what the form factor
is, or how it interfaces to the PC (USB, PCI, ISA etc.) - I just want to
minimise the cost. Can anyone suggest the lowest cost way of adding a lot of
digital I/O to a PC?

Thanks - Rowan

From: Stef on 18 Jan 2010 08:36
In comp.arch.embedded,
Rowan Sylvester-Bradley <rowan(a)sylvester-bradley.org> wrote:
> I have to create a test harness to allow automatic testing of a system that
> I'm working on. It needs several hundred digital inputs and several hundred
> digital outputs. They don't need to be isolated or anything - just logic
> input/outputs. I don't mind much what it looks like or what the form factor
> is, or how it interfaces to the PC (USB, PCI, ISA etc.) - I just want to
> minimise the cost. Can anyone suggest the lowest cost way of adding a lot of
> digital I/O to a PC?

Lowest hardware cost? Probably a bunch of shift registers connected to the
parallel port and bit-bang. It will be slow and you need to do your own
software, but the hardware will be cheap.

--
Stef (remove caps, dashes and .invalid from e-mail address to reply by mail)

"Roman Polanski makes his own blood. He's smart -- that's why his movies work."
-- A brilliant director at "Frank's Place"
From: rickman on 18 Jan 2010 09:35
On Jan 18, 7:02 am, "Rowan Sylvester-Bradley" <ro...(a)sylvester-
bradley.org> wrote:
> I have to create a test harness to allow automatic testing of a system that
> I'm working on. It needs several hundred digital inputs and several hundred
> digital outputs. They don't need to be isolated or anything - just logic
> input/outputs. I don't mind much what it looks like or what the form factor
> is, or how it interfaces to the PC (USB, PCI, ISA etc.) - I just want to
> minimise the cost. Can anyone suggest the lowest cost way of adding a lot of
> digital I/O to a PC?
>
> Thanks - Rowan

Like Stef said, if you want to make your own boards, you can use a
variety of chips. I think I would consider I2C or SPI controlled I/O
chips. There are a number of them available up to at least 16 I/Os
per chip with control over the output state as well as being able to
tristate them. Probably the cheapest way to get I/Os is to use MCUs
with a high pin count and low cost. They could be treated like "smart
shift registers" but with a lower cost per I/O. Selecting a device
that has a lot of I/Os and little memory should minimize the cost per
I/O.

FPGAs could be an option, but I don't think they will be as cheap per
I/O as MCUs. But they might be worth a look. The low end members of
the newest families could be in the running. With an FPGA you get a
lot of flexibility for specialized interfacing.

Rick
From: 1 Lucky Texan on 18 Jan 2010 11:32
On Jan 18, 6:02 am, "Rowan Sylvester-Bradley" <ro...(a)sylvester-
bradley.org> wrote:
> I have to create a test harness to allow automatic testing of a system that
> I'm working on. It needs several hundred digital inputs and several hundred
> digital outputs. They don't need to be isolated or anything - just logic
> input/outputs. I don't mind much what it looks like or what the form factor
> is, or how it interfaces to the PC (USB, PCI, ISA etc.) - I just want to
> minimise the cost. Can anyone suggest the lowest cost way of adding a lot of
> digital I/O to a PC?
>
> Thanks - Rowan

Dunno it it would be in your budget, but you could get one of these;

http://pc104.winsystems.com/products/ISA-PCM.cfm

then stack some of these on it;

http://pc104.winsystems.com/products/PCM-UIO96B.cfm

but probably $$
From: linnix on 18 Jan 2010 12:30
On Jan 18, 4:02 am, "Rowan Sylvester-Bradley" <ro...(a)sylvester-
bradley.org> wrote:
> I have to create a test harness to allow automatic testing of a system that
> I'm working on. It needs several hundred digital inputs and several hundred
> digital outputs. They don't need to be isolated or anything - just logic
> input/outputs. I don't mind much what it looks like or what the form factor
> is, or how it interfaces to the PC (USB, PCI, ISA etc.) - I just want to
> minimise the cost. Can anyone suggest the lowest cost way of adding a lot of
> digital I/O to a PC?
>
> Thanks - Rowan

We are doing something similar, perhaps we can work together.
We are using a 40 pins multiplexer with 26 I/Os driven by 4 lines:
serial output data, serial output clock, serial input data and serial
input clock. We only need one chip in each unit, but you can drive
multiple chips from the same micro. You can tie the data lines
together, so each additional chip only need 2 clock lines.

email: linnix at live dot com
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