hrm, have I made an error of judgement in assuming that the SSR I bought is in fact opto-isolated?
On Aug 22, 8:17 pm, Modena <b...@holnet.net> wrote: > Frank, so my basic understanding is that the opto-isolator you speak > of is an SSR, if this is the case why do I need another relay in-line > after the SSR? > > I tried today hooking up output to an automotive relay, which produced > weird results, no doubt because the relay could not switch fast > enough. Then I tried a 12v SSR, less weird, but it still stays "on" - > again, reverting to just the LED and all was well. > > On Aug 22, 2:09 pm, Frank Pittelli <frank.pitte...@gmail.com> wrote: > > > > > Modena wrote: > > > testing the circuit with an LED works fine, but when I hook up my > > > actual 12v valve, it must be causing interference or something because > > > pressing fire and the circuit switches on, and stays on indefinitely, > > > hence the valve stays open. > > > > anyone have any ideas how I might filter this? > > > You need to isolate the load from the logic. There are three basic > > solutions: transistor, logic-level FET or opto-isolator/relay. > > > If the load isn't too big and you like ruining lots of circuitry trying > > to make things reliable, a simple transistor can be used. There are > > deceptive devices, however, and when you think you've got them working > > properly, they bite you. There are dozens of circuits on the web, which > > tells you just how many people have tried to design the "perfect" > > transistor switching circuit. > > > The new kids on the block are logic-level FETs (I think they have a more > > official name) have been designed to be fool-proof, allowing logic > > circuits to directly drive a high current FET. They have all kinds of > > safeguards built into them (designed to eliminate the need for all those > > fancy transistor circuits mentioned above), but I have yet to find one > > with good old-fashioned solder leads ... they all seem to be tiny little > > surface mount packages. If you find one, let me know, because I'll use > > them for everything. > > > The approach that I've used the most (along with Dr. Sommer) involves an > > opto-isolator IC and a relay. The logic triggers the opto-isolator (5v, > > very low current), the opto-isolator triggers the relay (usually 5v or > > 12v, 100ma or so) and the relay triggers the load (any voltage, any > > load). It sounds like a lot, but it's quite simple once you've wired it > > a couple times and it is one of the most reliable switching approaches. > > > Frank P. --~--~---------~--~----~------------~-------~--~----~ You are currently subscribed to the "R/C Tank Combat" group. To post a message, send email to rctankcombat@googlegroups.com To unsubscribe, send email to rctankcombat-unsubscr...@googlegroups.com Visit the group at http://groups.google.com/group/rctankcombat -~----------~----~----~----~------~----~------~--~---
