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 <[email protected]> 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 [email protected] To unsubscribe, send email to [email protected] Visit the group at http://groups.google.com/group/rctankcombat -~----------~----~----~----~------~----~------~--~---
