At 11:37 PM 5/25/02 +1200, Russell McMahon wrote: >The current "winner" is a CD4094 serial to parallel shift register plus 3 >CD40106 inverters (half a pkg) plus a few R's and C's to derive clock, data >and latch signals from a single serial line. Positive going pulses are sent >from the controller. Pulses over a certain duration are seen as 1's, less >than this are 0's. (0 = nominal 1 ms high, 1 = nominal 3 ms high. Barn door >accuracy timing easily separates these. In practice 0's may be much shorter >if desired. As the data feed is interrupt driven these timings would be >used. Cessation of data for more than a certain period (say 10 ms) results >in latching of the data sent. ICs would be SOIC pkgs. Smaller not really >needed. The spare inverters will be used in other circuitry. Parts cost is >about $US0.40 (4094 + 40106/2 + glue). Given your cost constraints, this is the way I'd do it. I only see the need for 2 Schmitt trigger inverters: Clk and latch inputs on the 4094 require fast edges. You would be able to eliminate even those if you can find a cheap SR with schmitt trigger inputs. Higher end SRs do have those (I'm thinking of the TPIC6x595 family) but those tend to be much more expensive than the parts you have chosen. You don't need a ST on the data input to the SR - so long as the level is a solid 1 or 0 when the clk pulse comes, the 4094 is happy. Glue is 2 Rs, 2 Cs and 2 diodes - the diodes could be eliminated if you were willing to ensure that the rest time between bits and bytes was long enough to completely charge or discharge the RC delays. I wouldn't bother - adding the diodes costs hardly anything. dwayne dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 18 years of Engineering Innovation (1984 - 2002) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body