On 4/16/08, Dennis Crawley wrote: > Hi fellows, > > I'm trying to desing a very simple SR circuit to control two 24VDC signals > coming from two CAMs inductive sensors) and one 24VDC output which is > connected to a PLC input. (noisy machine) > > In most of the desings I've ended up with this (block) configuration > opto--\ > logic--opto > opto--/ | > | > source (taken from PLC) For me, looking to your description very fast, the optocoupling section hasn't too much sense. Assuming you are already use two optocouplers why do you need another 555 for an RS latch ? I gues SR for you is meaning SET-RESET latch, right ? You can do it directly with optocouplers supplied from 24V. Look to this ideea (which is not a genial one): http://graffiti.virgin.net/ljmayes.mal/var/optoltch.htm However depends what kind of signals are available at your inductive sensor output. > > For the logic part I used a 555 with reset and trigger tied to positive > through 100K resistor. > Since the 555 used 18V max,... I have calculated a 18v1w zener with a > 100ohm1/2W resistor limitation to power the kit. > > I've also thought about a 12F, but I don't want a DC-DC converter,... unless > it would be the best and safer way to do this task. > > True table > S R Out > REdge x 1 > x Redge 0 > > Is there any chip out there that works over 24VDC directly? > Should I have to desing this with Op amp? > The challenge is to desing the SR on the 24VDC rail, > with the less number of componentes as possible. > > I'll appreciate any hint . > > Cheers regards. > Dennis (lurker) > > > > > > > > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist