Michael Chare wrote:
Is there a little box that I could buy which would have an Ethernet port (and
IP) that I could attach to my home network and would allow me to use my computer
to monitor the status of the mains voltages circuits (of my central heating
system)?


From http://www.cpc.co.uk
Description Order Code price (ex. VAT) each
NETIOM Card CS11740 £60.54
LED Module CS07632 £9.67
Relay Module CS07633 £17.81
Null Modem Cable CS00179 £1.71

NETIOM Input/Output Module
NETIOM is a stand-alone, network aware input/output card which can be
controlled over most networks including an 'always on' Internet
connection. It can act as an HTTP server with up to 32K of webspace,
generate e-mails in resonse to specific events and act as a client to a
remote server. An ideal product to integrate into home automation,
local/remote process control, environmental control, security monitoring
and machine monitoring and control.

16 Digital (TTL/CMOS/Dry contacts) and 4 analogue (10bit resolution,
max. 5 volts) inputs

16 Digital outputs (open collector 50V dc50mA)@BR
The outputs can be connected via headers to either the LED module
(provides indication of outout on 8 LEDs) or the Relay module (provides
8x SPCO relays)

RJ45 connection to network (10MIPS)

9 Way male D Serial port (2400 to 38400 baud - handshaking not
supported) (Null modem cable required for programming)

Watchdog mode allows NETIOM to monitor network connections and operate
outputs when failure is detected

Automatic detection of IP address (DHCP)

Web space can be password protected

All inputs/outputs via screw connectors
Contents: Card, driver and user guide software

HTH!

--
Adrian C