Jack,

How large is the transformer ?

I should also have mentioned, I have limited space (around 25mm x 25mm). If
I could locate a very small
transformer it may work.

My main concern for isolation is that if the Phase and Neutral are reversed,
I do not want 230 VAC on the ground
as it is common to an RS485 interface and some other IO circuitry.

There is no problem conditioning and processing the signal once I can ground
reference it.


-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf
Of Jack Smith
Sent: Saturday, 30 July 2005 11:17 AM
To: Microcontroller discussion list - Public.
Subject: Re: [OT] Circuit for measuring mains voltage


I've had good results with a transformer feeding a Maxim MX536A
RMS-to-DC converter, which I then read with the 10-bit ADC in a 16F877A.

The MX536A converts an AC input into a DC output equal to the RMS of the
input, e.g., a 1 V RMS input provides 1V DC output. Hence, in your case,
to have a 2.5V DC output correspond to 270VAC, you will need a suitable
step down transformer, which will provide the isolation you need as well.

Jack



Groups wrote:

>I am looking for an isolated method of measuring mains voltage (230VAC).
>
>First thoughts are a Opto coupler running in its linear region ?
>My concerns are that the transfer ratio degrades over time.
>
>The circuit needs to provide a fairly linear response from 150VAC to
270VAC.
>The output required for the Micro is 0-2.5V.
>
>Any ideas for existing circuits much appreciated
>
>Thanks in advance
>
>Regards
>
>David
>
>
>
>
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