On Wed, 24 Oct 2001, Robert J Gautier wrote:
Depending on the machines, you could build a thin client network but you would need a reasonably beefy server, say £800 on the hardware. Also it is really necessary to have at least 1 meg of video RAM in the client machines and 2 meg is better, in order to run the X graphical interface. 10 meg ethernet to a 100 meg switch and then to the server should be more than enough. If you're really building a data logger then I can't see the need to run an X server. Maybe X *clients*? But probably something simpler, even a little HTTP server, would do the job. If you really want a desktop then you're building desktop machines that can do data logging, which IMHO is a different thing; the unpredictable activity produced by the desktop clients would tend to make the timing problem harder. For me the trickiest parts of doing a data logger would be interfacing to the sensors and perhaps getting a stable enough timebase. I've driven parallel I/O such as printer ports from userspace quite successfully (polling rates around the 1000Hz mark) from Tcl, and I'm sure Perl etc. would do the job too, and provide an HTTP interface, on a very small box.
We will be doing the development work for the data logging and control part of this project. The plan is to create tiny servers to run on the machines physically connected to the data logging equipment, communicating with a selection of front-end programs via TCP/IP. We are aiming to create a standard interface to a variety of data logging equipment so that the front-ends can use any type of temperature sensor without having to be aware of all the different makes, models and protocols that the various bits of educational data-logging kit use. For the control side, we plan to extend Squeak since it already provides a near-perfect environment for manipulating objects graphically, building programs using drag-and-drop, etc. Only problem is processor load: it requires something of the order of a 700MHz CPU to run a single front-end. Fortunately, this applies only to the computer running the front-end - in the case of a thin-client system this would be the central server and the client workstations would be more than capable of running the tiny servers that actually talked to the hardware. Michael