Jinx,

Yes, that is the device (VB0.35XXX) I had noticed from Farnell.

The 230VAC input voltage monitoring part of my application is to be used as
a low voltage alarm to indicate
when the voltages supplying a motor fall below a programmable value. It will
have 270VAC MOV on the primary
to limit transients.
The secondary will be fed via bridge to a smoothing cap and burden resistor.
Next a series R to Op-Amp with a smaller
cap for additional smoothing and Zener for over voltage protection.
The op-amp gain will be adjustable to set a specific Vout at 230VAC.

As long as the DC voltage recovered is reasonably linear from 230VAC down to
about 150VAC we can get the results
we require.

Regards

David

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf
Of Jinx
Sent: Saturday, 30 July 2005 2:23 PM
To: Microcontroller discussion list - Public.
Subject: Re: [OT] Circuit for measuring mains voltage


> I think I will look into small transformers. Farnell list one from
> "Block" that is 22mm x 22mm that looks suitable

Sounds like the one I got from RS. Be aware that it saturates
and you need a series resistor. Mine was nominally two 6V
secondaries but put out 73Vp-p. The lowest picture shows
two primaries in series to give the approximately expected V
out

http://home.clear.net.nz/pages/joecolquitt/block-tx.html

Russell suggested, during [EE] Block miniature transformer
in May '05, that

"Placing a 0.5 watt load on the transformer secondary and a 24k
resistor in series with the primary MAY produce approximately the
desired result"

Block themselves confirmed that the small Tx would generate
less heat with a load

I regret that that particular part of the project got sidelined
during my battle with the F88 and I2C, but it is back on the
agenda and I hope to do some experimenting ASAP


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