Cheap protection...

[Mike (Perth, Western Australia)]

At 06:25 PM 26/3/2000 +0800, Bernd Felsche <bernie at perth.dialix.com.au> wrote:

>>Well, another option is to use a protected MAX232 RS-232 input/output
>>chip, this already has lots of ESD protection and overvoltage too,
>
>That's novel. A bit pricey though. Works out about twice the cost
>per input as opto.

Well that depends - are you doing a one-off or designing a commercial
product. In production MAX232's can be got for about A$1.50 depending
on volume ?  Its relative to the cost of EFI controllers...

>I was aiming at $20 in parts for the lot (well, about $25 including
>the case). The uC is about $6, though I might have to spring for $10
>on the prototype as the "best type" is not yet available...

Sorry, I think I missed an earlier email on this, I take it this is not
for an EFI project, what are you building - is this the WI project  ?

>>depending on the source impedance you'd probably also want a series
>>resistor to the MAX232 input.
>
>What's the source impedance of a car battery? :-)

mmmm ! If you are measuring battery voltage then a MAX232 will not work
as its a discrete signal conditioner not for measurement of an analog
voltage. Since you want to measure battery volts, then a simple
divider and large caps would be sufficient...

Rgds

:) Mike

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