OT: What am I meant to be googling for?

[Peter B]

My google mojo is failing me today, so maybe the assembled experts can help...

I'm idly looking for a PCI card or USB device that can take as input the

230v/3A switched live from a thermostat. The intention being to be able to poll the input(s) on the PC and thus monitor when zones are calling for heat.

What combination of search terms might give me something useful? I'm coming up with an awful lot of un-related nonsense at the moment.

The programming side I'm fine with, I just don't know what the "thing" to talk to might be called.

[F Murtz]

You would be better off converting your input to something that existing computer inputs can handle, or is that converting device what you are looking for?

[Tim Watts]

"USB isolated" maybe - and I'm pretty sure Maplin have some not too expensive modules that do this.

[Jón Fairbairn]

Couldn't you do this with a resistor, and opto-isolator and an Arduino? (Someone else can say whether this can be made safe). The Arduino might be overkill, but I've found it cheaper to use one of them than to buy a specific USB controlled switch, for example.

[The Natural Philosopher]

ADC peripheral card

[Peter B]

It could well be what I'm looking for; at the minute I *know* that I've got switched lives at one end and a computer at the other - I just don't know the name of the thing that would sit between the two and allow monitoring.

[Man at B&Q]

A relay.

MBQ

[Peter B]

Oh my, I think you've just found a new way for me to waste far too much time. All I had to do was google "arduino" and my family won't see me for a week! Interesting stuff

Like I say, I know what I want to do, but have no idea what the enabling bit in-between might be.

[newshound]

Neat looking bit of kit, that's completely new to me.

I was going to suggest a Little Doctor, but that looks better / cheaper

[tinnews]

I almost went down the Arduino route recently until I found the 1-Wire bus which makes such things even simpler.

The 1-wire bus is just what it says, a simple serial bus and protocol that can access devices on a simple twisted pair (i.e. 1 wire plus return) bus. You can get ready made USB or serial port interfaces and there's also ready made software to read data from the devices on the bus. (look for digitemp, owfs and others)

[Andy Dingley]

The two don't contradict. It's pretty easy to combine one-wire or I2C with the Arduino. One-wire's advantages were mostly for the sensor devices, rather than the processor. I've pretty much abandoned my old TINIs for Arduinos nowadays.

[Andy Dingley]

No, you really don't want to do that - it's not 1990.

• AD converters belong near the sensor, with a digital link back to the hub. Avoids a lot of noise and signal conditioning problems, and these days it's cheap.

• "Cards" are obsolete. Whatever it is, it'll be USB attached, not internal.

• Most "ADC peripheral cards" surviving these days are high-end, high- quality kit with steep pricetags. You just need the cheap stuff today.

Mind you, if your sgnals are dynamic, cheap USB oscilloscopes (data capture pod, display on the PC) are very cheap nowadays if you buy them direct from China or via eBay.

[tinnews]

Yes, but if you have a PC (in my case an old eeePC) already dedicated to reading the devices an 'extra' computer (the Arduino) which needs at least some configuration and programming is overkill.

I.e. with an Arduino configuration you have:-

PC -> Arduino -> sensors

Whereas with the 1-wire bus you have:-

Pc -> sensors

OK, if you set up so the PC can be turned off and leave the Arduino running then that may be the sort of system you want but in my case the PC is going to be on all the time to provide a web server interface to access the sensors so an extra system in between makes little sense (and for me anyway the eeePC with Linux on is a very familiar environment to configure).