@ Modena: Also don't forget the appropriate resistors on the base and collector
On Sat, Aug 22, 2009 at 10:40 AM, Don Shankin <[email protected]> wrote: > @ Frank: > > Are you talking about MOSFETs? They're essentially voltage-controlled > transistors (as opposed to being current controlled). They can be had with > an extremely low "on-resistance" which makes them ideal for very high > current applications, since they dissipate much less heat than an equiv. BJT > (if you can even find an equiv. BJT with the same current handling > capability). Another useful feature is because they're voltage controlled, > you can wire many of them in parallel to essentially make one huge MOSFET > (this is how the open-source motor controller is able to handle several > hundred amps of current draw and still stay cool) They certinally exist in > through-hole packaging. You can check out Digikey, or Futurlec (where I get > all of my components from). Here's a link: > http://futurlec.com/TransMosIRF.shtml They can be a little pricey, but > they have pretty impressive characteristics. LoL @ "new kids on the block" > > @ Modena: > > I'm guessing that your problem has to do with the fact that you're trying > to switch a 12v valve with a 555 timer that's running on 5v. You should > place a small NPN transistor (like a PN2222 or similar) between the 555 and > the valve. Connect your 12v source the collector and your 555 output to the > base. Connect the valve to the emitter. Give that a try > > > On Sat, Aug 22, 2009 at 5:26 AM, Modena <[email protected]> wrote: > >> >> 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 <[email protected]> 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 <[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. >> >> >> > > > -- > ---------- > Donald Shankin > Computer Engineering Undergrad > Blue Marble Security Member > IEEE Vice Chair, MTU Chapter > NSBE Telecommunications Chair, MTU Chapter > CAEL Partner > (507) 301-2499 > [email protected] > [email protected] > ---------- > -- ---------- Donald Shankin Computer Engineering Undergrad Blue Marble Security Member IEEE Vice Chair, MTU Chapter NSBE Telecommunications Chair, MTU Chapter CAEL Partner (507) 301-2499 [email protected] [email protected] ---------- --~--~---------~--~----~------------~-------~--~----~ You are currently subscribed to the "R/C Tank Combat" group. 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