Re: Liquid level indicator

Hi Chris

Thanks very much for taking the time to explain this for me, and offer
improvements.

I've printed off your message and ccts from notepad for a thorough
read.

If you can suggest a good electronics book which explains transisters
very well for beginners/noddy's, that would be great.

You may be right about the foam, but I'm hoping to build the U/back and
hop back in such a way that I get minimal foaming - hopefully I can
achieve this.??

For my cct, I need to drive the relay from two sensors - a high and low
water mark, and I'd like to provide both a reset and an override ("just
turn the pump on") feature. Furthermore, I'd like to be able to use
the same cct and switch between the underback sensors and the hop back
sensors (DPDT switch?). It may be that I'll need two separate sensor
ccts for this, as each may need to be calibrated separately. Dunno.

Any suggestions you have here would be very welcome! I did draw up a
truth table for the kind of logic I think I need, here
http://www.mcgee-family.com/projects/BreweryDesign/brewery_overview.htm
(go to the bottom of the page for the table).

This means that I need an assortment of AND, OR and INVERTER gates. I
know each of these can be built from NAND gates (IIRC OR gate made from
3 NAND's), but this is a bit messy. Any suggested improvements here
would be very welcome too!

I forgot to include schmitt triggers on some of the switched inputs, so
I guess a schmitt NAND like the cct above or a dedicated schmitt
trigger is in order here?

Cheers,
Mark

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