I have a quick speculative question, as everyone is so helpful on these boards! Thank you for all the help over the last few months, it's been priceless.
Basically I was wondering if it might be possible to use a relay and an arduino to rig up a system in a workshop so when the trigger on an electric sander is pressed, it automatically starts up a dust extractor, some sort of automatic sensor? I get the feeling it should be possible but I'm not sure how to start thinking about it. Has anyone seen a similar project? Am I re-inventing the wheel here?
You can buy a pre-built power bar that will do this. You plug you extractor in slot A and sander in slot B. When the box sees a load on B, it switches on A.
You could sense the current running through the wire going to the sander and use that to activate the blower. But something like the gadget gardner mentioned would have to be easier if you can find one.
Ok, i found a UK equivalent here: http://www.diytools.co.uk/diy/Main/sp-1-977-50281-record-wve002-auto-switch.asp?iBrandID=123&iCategoryID1=977 for a staggering £140. The Boss at the company I'm interning at bought one and told me to take it apart. He wants me to try and build three or four using standard components. So I open the lid of this thing to find out what could possibly cost so much when the American equivalent is about £15...
Eep! What is all that stuff? I put some serial numbers into google and found out there's a microcontroller, the relay (as expected) at the back, a load of capacitors, but beyond that i'm stumped. Is this a safety thing? How do I even start constructing something like this? Do I tell my boss just to pay up and buy some more of these?
Any hints, insights or comments really really welcome!
Measuring the voltage drop on a resistor is a bit tricky to get right since it involves connecting directly to one of the current carrying mains lines -- even if it is the neutral.
If it were me, I would have a go at running two turns of heavy conductor through a ferrite core, and then a few turns of magnet wire as a current sensor. On the sensor side, a rectifier, 300 ohm resistor, smoothing cap and a 5V zener diode shunt, to yield a TTL compatible signal.
You run your load through the primary winding -- on the neutral side is fine.
Thank you so much everyone! Some good advice there. The U1 is a 7FLITE05ML, the other number on it is 929808.
I may just advise my boss to buy some more expensive ones. I've already bought that intelliplug, but it has a 5 second delay which makes it unusable. The inside looks similar, once i hacked past the security screws.
I'll keep exploring this, while i want to impress my boss I don't want to cause a fire...
Thank you for your perspective on things, it makes me think i'm giving up too easily. There's a vacuum cleaner which does this function as an add on as well, I've been told i can have a look inside there also, so maybe it'll be simpler. I think the other two have a built in delay one way or another which might make them harder for me to replicate.
In other news, my solenoid project is nearly done! It works well, even if the box is a little rickety. Thank you for all the support for my projects.
I think you should connect a microphone to the arduino, and detect the "generally loud" loudness of a machine in operation, and drive a solid-state relay of some kind for the extractor.
(Turning off might be a problem, since the sound of the extractor is probably high enough to keep itself on.)
Haha! an intriguing idea, it might be a bit self perpetuating like you say.
Well, i found a board designed for the job ready made, thing is my boss wants me to connect it up and include some sort of hanger switch things so that when the sander is hung up it turns everything off.
The thing is, when the sander is not switched on, the extractor is not switched on, so nothing is drawing any power, right? The whole device is switched on at the wall but shouldn't be pulling anything in the "off" state, correct? Unless the relay board itself draws power, and I'm not sure if it does or not.
I know arduino does, and there seems to be a little micro controller on the board too, so might this draw power itself? Is a second switch really necessary? (putting a switch inline with mains power seems pretty risky to me anyway, so it would need a second relay I think.)
