Data logging efi

[am018]

Yes the 8 line AD convertors with built in multiplexers look tempting
and some of them are half-flash and have on chip sample and hold which
is really a good idea  in this type of application but --
I've explored both routes and  have both up and running -- the TLC548 is
by far the simpler   only 3 wires  (not counting power and earth) it
also the advantage of being dirt cheap  and giving reasonable speed mine
is reading data accurately  at 20khz+  --- it also seems to be quite
robust and unfussy about power supplies in contrast some of the 8 output
line convertors seem to draw a lot of juice.   :-)
On the otherhand the downside of the 3 wire types like TLC548 is driving
it in software  reading one bit at a time. :-(

Can the 8 data bits on a bi-directional port be used easily as inputs
from an ADC ? I haven't tried myself  having been informed from a couple
of sources that it wasn't as easy as it would appeared -- this info
might be wrong but I have established  the bits  are normally in a  high
state and the easiest way to read data in from them is by pulling them
from high to low.
When I built my  8 output line convertor  I was advised to  interface
using the handshake lines in 4 bit chunks via hex buffers----   it works
well  but isn't very elegant and involves a lot of bit manipulation in
software. :-(



Regards
Andy Macfadyen
(about to go off on holiday !)  (|:~)




Jake Sternberg wrote:

> you can look in the radio shack mail order electronics catalog
> (called "TechAmerica") and pick an A/D chip out.  They have a
> real nice one with an eight-input multiplexer (connect eight
> signals to it and it will allow you to digitally select them)
> and an 8-bit output.  If you have a two-way parallel port on your
> laptop you should be able to wire this thing up to it with no
> other devices.  try to power it with +5v from the computer though,
> like from the keyboard socket, to be safe.
>
> -jake
>