Re: Two quick RS-485 questions

I think a current loop might be your cheapest option. You would need a proper 'driver' at the TX side while all receivers are merely cheap optocouplers at a fraction of the price of an RS-422/485 receiver. And as a bonus, you'll get galvanic isolation for free.

With 2400 bps and a current loop you could even use fence wire. So yes, cat5 will be fine :-)

Meindert

Ah, but I'm required by the customer to use RS485, sorry. I should have made that clearer in my original posting.

BTW, the driver/receiver I'm using is the SN75LBC179P, which is $1.26 in 25pc quantities, not too bad. I just finished a nasty prototype PCB layout and created the BOM, and I find that as long as they make at least 10 of these, it's going to be _way_ cheaper than my ballpark guess. Since they already have purchase approval for the ballpark guess, I come out looking like a hero for being under budget ;)

That is indeed cheaper than the Maxim counterpart.

:-)

Meindert

Cheapest is probably a generic 75176, e.g. DS75176BM or SN75176AD, ~ $0.20 each / 100.

Where do you get new ones for that price? Cheapest I have seen is double that.

Thanks, Joe Legris

Digikey has the TI ones for 0.21 in 500, should be possible to do better.

Best regards, Spehro Pefhany

There is some reason why I chose this particular part, but I didn't make a note of it. (I have a half-page of scratch paper with part numbers on it, most of which are crossed out). Well, anyhoo, I'm about $30 per unit under budget for the entire appliance, which is great heaping bowls full of meaty gravy, and there is much rejoicing.

But in qty 100 they're 38 cents each.

-- Joe Legris

Or maybe they are 0.21 each with a $17 line-item nuisance charge.

Best regards, Spehro Pefhany

EBV / Avnet in UK for SN75176AD / 150 pcs. Future in Canada for DS75176BM / 95 pcs.

This was in late 2003, so I suppose prices might have changed a bit.

FAI's web site price is about triple that.

Best regards, Spehro Pefhany

Really? Well, this wasn't off the web site, it was a direct quote. Perhaps there was a glut of them at that time.

Web site prices tend to be on the high side compared to distributor quotes in combination with other stuff (juicy total order size), at least in my experience.

Best regards, Spehro Pefhany

While were talking about prices, what's the best choice (i.e. cheap) for a MAX232 equivalent that the uses 0.1 uF caps?

Thanks, Joe Legris

Joe Legris wrote: : While were talking about prices, what's the best choice (i.e. cheap) for : a MAX232 equivalent that the uses 0.1 uF caps?

ST232 ? (SGS Thomson,

-- ****************************************************** Never ever underestimate the power of human stupidity. -Robert Anson Heinlein

snipped-for-privacy@INVALID.and.so.forth ******************************************************

Best I found was ST232CW or (TI) MAX232D for ~$0.50 for ~50 pcs. (Would be interested in others).

Sipex SP232ECP, last buy was ~$0.53 each.

For some further information about RS485, check out this app note. It describes 10 ways to "bullet proof" RS485 interfaces.

Regards David Milne