> Every decade or so it seems time to again see if relays have
> finally had their day.

Don't think they have, nor will do for a while yet. Metal-on-metal
switching is just so simple and efficient

> Digikey & maybe Mouser cheaper still but minimum order prices
> apply to avoid crippling freight costs

DK to NZ can be expensive. Mouser via Active Components is
surprisingly cheap. My last order (~$150) was $4.50 freight, as
it's just the local courier from Auckland North Shore. AC pick up
the import freight as they are the Mouser agent and receive small
orders as part of a regular consolidated shipment anyway

> DO NOT trust the ratings of the incredibly cheap opto isolated
> Chinese modules being sold for "maker community" use.

The product isn't particularly price-sensitive. The query is partly
about getting the height profile down if possible so it can be put
into a better-looking panel-mount fascia. The relays I used were
tall-ish, about 22mm, I bought out Dick Smith's stocks at a
clearance price when they phased out most components

Jean-Paul's driver IC suggestion is a good one, but looking over
the circuit it's going to be awkward to implement because of the
inter-connectivity of 3 relays. Apart from all extra circuitry and
board space there are the voltage losses too. If the circuit was
simpler I'd give it a go.

I might still look at discrete FET H-bridges, but low-profile DIP
relays (my preference) should be acceptable

Joe


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