Using a current to activate a switch - Page 1
Forum section: electronics / beginners

author: beginner
author_rank: Contributor
timestamp: April 16, 2014, 08:11:58 am
content: Hey Guys,You can probably tell by the question I'm total beginner here - I am working on only my second project and am some of the way along getting it all together, have run into a couple of small hurdles for now. Basically what I am attempting to achieve is to integrate a raspberry pi with an old boombox - like a sort of semi DIY sonos.Right now where I'm at: I've got stable power to the RPI from either 240v or battery (at the moment 9v) sources, have a DAC sorted out andwired into the amp which is putting out some decent sound, as well a basic on/off (basic as in it just kills the power to the whole thing). Simple enough, all runs, does the job OK and hasn't caught fire, but needs a few things before I put the cover back on it all.Where I'm stuck: I've got a reasonably clever switch for the pi which is fairly basic in operation : When the + and - are closed the switch gives the signal for the pi to soft shutdown, when done the power to the pi is cut. Obviously power required to be present make this happen, so my kill switch won't work.What I'm thinking: My box has a couple of components (FM receiver / tape). These are activated by flipping through the various positions on the selector switch. This selector is soldered onto the board with a whole bunch of pins and appears as though it works by completing the selected circuit, I've considered rewiring this but not sure of the implications.It does so happen I have removed the FM board to make space for my own gear, this has left me with a couple of now unused wires giving me 8ish volts when this function is selected. This selector does have an 'off' position which cuts power to everything (I have accessed power for the pi at a point unaffected by this switch)I've previously used an optocoupler to activate a switch similar in function to what I have here, in principle this appears to me as pretty much the same case and my first thought was to do the same thing, however the voltages involved are somewhat different.So, my basic question is - is my solution at all sensible and if so, what should I look into to complete a very simple circuit for me based on the presence of 8ish volts. Also interested in what may be most efficient considering the thing can run on batteries.Just to add I'd like to keep things as simple as possible for this project and see how it goes, if I find some success I'll take it all a step further on one of the more serious boxes I have lying around. Apologies for the length! Thanks guys!

author: miguelvp
author_rank: Super Contributor
timestamp: April 16, 2014, 08:16:09 am
content: Just to say, i'm amazed no one took the nick beginner until now

author: beginner
author_rank: Contributor
timestamp: April 16, 2014, 08:27:00 am
content: Quote from: miguelvp on April 16, 2014, 08:16:09 amAs was I, think this is actually the first time I've ever actually got it

author: ve7xen
author_rank: Super Contributor
timestamp: April 17, 2014, 07:41:56 am
content: Thanks for providing details, but your actual question is kind of lost in the post. What are you trying to do, exactly?It sounds to me like:- You have a control signal that goes to 8V and is "open" when off- You want to trigger your power control circuit based on the state of this switchIf that's the case, we'll need to know a bit more about how your power control thing works. Probably you just need a small transistor or FET, but it's all down to what you actually need to switch.

author: beginner
author_rank: Contributor
timestamp: April 18, 2014, 04:43:07 am
content: Yeah I think you're dead on but just to confirm how the power control thing works -It's all independent to the 8v and operates with a basic toggle on/off switch. I wish to replace the toggle switch component with something which will be in the 'on' position when the 8v is present, and off when there's 0v.I do have another board I can use which operates using momentary push button on and off switches, i figured the toggle version would be more suitable though.Thanks!!