I missed most of this thread, and maybe you are already aware of some version of serial driver IC's, but I thought I'd mention the Allegro UCN5895. We have used it with good success. 16-pin DIP, serial in/out cascadable, separate power for logic/load, controls 8 relays. Gary Crowell Micron Technology -----Original Message----- From: Greg Peyton [mailto:Gpeyton@TEMPOCOMM.COM] Sent: Tuesday, June 27, 2000 6:10 PM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [EE]: Relay question...the continuing saga First off. My apologies for not using [EE] in my original post. I should've, even though this entire discussion does eventually lead back to a PIC. Secondly, I'd like to thank everyone, both on and off the discussion, for the responses to my post. The suggestions were extremely helpful. I had no idea the use of relay arrays was so widespread. My delay in responding is due to work on another project. Yep, we actually got real work to do during the week. This stuff counts as fun in my book. Now... I like the idea of using the 30 pin serial driver IC's. This keeps the chip count low and reduces the port pins being used. I might use this idea if some of the other more intriguing ideas don't pan out. Peter, I read your post using 373s and at first thought it was not much different from the original scheme I had in mind. After rereading it though...Whoahh! "MATRIX". Now we're onto something. This is what I'm looking for (at least for using the 373s). I'd like you to take another shot at describing how you get 32 relays off two 373s. I was with you as far as using the 6pins + 2 strobes but got lost on the actual matrix connections. I'm having some trouble visualizing that. -Greg Greg Peyton Metrology Lead Technician Tempo (760)598-8900 x293 gpeyton@tempocomm.com http://www.tempocomm.com >>> Peter L. Peres 06/27/00 02:35PM >>> ---------- Forwarded message ---------- Date: Tue, 27 Jun 2000 00:08:16 +0300 (IDT) From: "Peter L. Peres" To: pic microcontroller discussion list Subject: Re: Relay question... Hi, there is no need to use one driver per relay, with latching relays use a matrix. For 32 relays you could use 2 x 373 as latches, with 6 data bits used in each, and two additional PIC pins used as strobes (total 8 pins used - but see below for a solution using only 3 pins - chip count == 2 n/incl pic). A set of diodes are required at the drivers to remove the kickback problem. These are available integrated (in nines even). To steer the array you first strobe one side of the matrix, then the other, then turn it off. If you need to steer all the relays statically (not latching) then it might be better to use a serial in parallel out shift register, or rather many of these, chained. You'd need four for 32 IOs, using only three PIC pins. You can use only two shift registers for a matrix of latching relays (8x8 = 64). This I have done (with 20 latching reed relays in a 5x4 crossbar matrix). Note that you may not need to use separation diodes in the matrix, because the phantom circuits will only have 1/2 Vcc or less applied and most bistable relays do not change state under these conditions (you need to check specs). Peter