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Groups > comp.sys.raspberry-pi > #12702
| From | rickman <gnuarm@gmail.com> |
|---|---|
| Newsgroups | comp.sys.raspberry-pi |
| Subject | Re: control a relay from the pi via GPIO |
| Date | 2016-07-12 04:23 -0400 |
| Organization | A noiseless patient Spider |
| Message-ID | <nm29ed$8f7$1@dont-email.me> (permalink) |
| References | <nljpg6$me8$1@dont-email.me> <nllbra$3ga$1@dont-email.me> <nltq7o$8kj$1@dont-email.me> <nlttuo$m3v$1@dont-email.me> <nm28f3$62f$1@dont-email.me> |
On 7/12/2016 4:06 AM, Björn Lundin wrote: > On 2016-07-10 18:43, rickman wrote: >> >> Info on this module is scant. Is there a reason why you don't trace out >> the circuit so you know for sure what the circuit is? It shouldn't be >> that hard to do. >> >> If you only have one transistor, the circuit you have is most likely the >> one Gordon is thinking of. But it is always possible not. Trace it out >> and we'll know for sure. > > Yes, there is a reason. I'm a software guy, > and although I do understand Ohms law, > when it comes to transistors, I'm lost. > > So I would not know where to start. > > >> >> It can be used with the rPi if you use something to limit the voltage on >> the I/O pin. A blue, white or UV LED would be perfect for this. As >> long as the circuit on the relay board has a resistor in the path from 5 >> volts to the input pin, the LED can safely clamp the voltage at that pin >> to about 3.3 volts protecting the rPi I/O. Use an IR LED in series >> between the rPi and the relay board and it will drop the excess voltage >> so the visible LED won't cause the relay circuit to activate. >> >> | | Relay _____ >> | | Module / | >> | IR LED | |_ --- >> rPi | | /| | |/ Gnd >> Header -->>----+-----|< |------<<----\/\/\-----| PNP >> Output | | | \| | |\ >> | _|_ | \ >> | \ / | | >> | V Blue, White | | >> | ----- or UV LED | C|| >> | | | C|| Relay >> | C|| Coil >> | | >> --- --- >> Gnd 5 volts >> >> If the circuit on the relay board doesn't have the resistor on the base >> you need to add it to your circuit, but I find that unlikely. >> >> The base-emitter junction of the transistor will drop 0.7 volts when >> forward biased. The IR LED will drop about 1.2 volts and the blue LED >> will drop around 3.4 volts. This adds up to more than 5 volts which >> means only a very small current will flow (your goal) when the rPi >> output is not pulling low. This should not be enough to pull in the >> relay. If the relay still activates without being pulled low by the rPi >> output, use a red LED in place of the IR (or add some series >> resistance), but I'm pretty sure this won't be needed. The relay needs >> significant current to activate and the transistor only has so much gain. >> >> Just an idea to let you use this module with your rPi. This circuit >> works for a lot of 5 volt circuits as long as a small trickle current >> won't trigger it. > > And this drawing is beautiful. However it is over my head. > But I really appreciate the effort Ok, sorry for making this complicated. Transistors aren't hard to understand if you get to the point where you would like to learn. -- Rick C
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control a relay from the pi via GPIO Björn Lundin <b.f.lundin@gmail.com> - 2016-07-06 22:24 +0200
Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-07-06 16:45 -0400
Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-07-06 17:03 -0400
Re: control a relay from the pi via GPIO Dennis <dennis@none.none> - 2016-07-06 18:00 -0500
Re: control a relay from the pi via GPIO Dennis <dennis@none.none> - 2016-07-06 21:10 -0500
Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-07-06 23:55 -0400
Re: control a relay from the pi via GPIO Dennis <dennis@none.none> - 2016-07-07 12:30 -0500
Re: control a relay from the pi via GPIO Björn Lundin <b.f.lundin@gmail.com> - 2016-07-07 19:21 +0200
Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-07-07 14:34 -0400
Re: control a relay from the pi via GPIO Dennis <dennis@none.none> - 2016-07-07 17:10 -0500
Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-07-08 00:29 -0400
Re: control a relay from the pi via GPIO Björn Lundin <b.f.lundin@gmail.com> - 2016-07-12 10:18 +0200
Re: control a relay from the pi via GPIO Rob Morley <nospam@ntlworld.com> - 2016-07-12 12:49 +0100
Re: control a relay from the pi via GPIO Gordon Henderson <gordon+usenet@drogon.net> - 2016-07-07 10:44 +0000
Re: control a relay from the pi via GPIO Björn Lundin <b.f.lundin@gmail.com> - 2016-07-10 17:40 +0200
Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-07-10 12:43 -0400
Re: control a relay from the pi via GPIO Björn Lundin <b.f.lundin@gmail.com> - 2016-07-12 10:06 +0200
Re: control a relay from the pi via GPIO The Natural Philosopher <tnp@invalid.invalid> - 2016-07-12 09:20 +0100
Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-07-12 04:23 -0400
Re: control a relay from the pi via GPIO The Natural Philosopher <tnp@invalid.invalid> - 2016-07-12 09:58 +0100
Re: control a relay from the pi via GPIO Graham. <graham-usenet@mail.com> - 2016-07-11 23:10 +0100
Re: control a relay from the pi via GPIO Graham. <graham-usenet@mail.com> - 2016-07-08 21:45 +0100
Re: control a relay from the pi via GPIO Björn Lundin <b.f.lundin@gmail.com> - 2016-07-10 17:26 +0200
Re: control a relay from the pi via GPIO Graham. <graham-usenet@mail.com> - 2016-07-11 22:13 +0100
Re: control a relay from the pi via GPIO Björn Lundin <b.f.lundin@gmail.com> - 2016-07-12 10:00 +0200
Re: control a relay from the pi via GPIO Big Bad Bob <BigBadBob-at-mrp3-dot-com@testing.local> - 2016-08-18 10:08 -0700
Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-08-18 16:40 -0400
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