Arduino to control switches

Using Arduino Project Guidance
1

I want to use Arduino to control the production of hydrogen/oxygen via electrolysis, and the condensation of water from a peltier cooler.
Presumably I'd need 4 things:

  1. A switch to initiate the electrolysis which I could control from Arduino
  2. A switch to initiate the peltier which I could control from Arduino
  3. The ability to measure how heavy the peltier gets (to know how much condensation has formed on it)
  4. The ability to measure the water in collection vessel so I know when the electrolysis should stop (when the water gets to a certain level)

Now I have found this for 4, but other 3 I am stuck on, and would like some assistance as to what hardware I should get to accomplish this.

2

Well, all this kind of depends on whether you're doing this on an industrial scale (with industrial explosive atmosphere considerations), or at the kitchen sink with some old coffee jars.

3
  1. A switch to initiate the electrolysis which I could control from Arduino

This depends upon the voltage and current of the electrolysis process. Or are you asking about how to do the actual electrolysis?

  1. A switch to initiate the peltier which I could control from Arduino

Same as above: what did you have in mind? My guess is that it's low-voltage high-current DC in which case a MOSFET would work, or a relay.

  1. The ability to measure how heavy the peltier gets (to know how much condensation has formed on it)

What kind of weight difference are you looking for? A change of a few grams, hundreds of grams? Most accurate, and most expensive, are going to be load cells. You will get by more cheaply with a force-sensitive resistor (FSR), like part SEN-09376 at Sparkfun. Those tend to be a bit wonky to work with as they "settle", age, have to be broken in, etc.

--
The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons

4

Narwhal:

Your project is really not well defined. The title says it is about switches -- but you want to weigh something as well -- the weight of a vessel and the height of a liquid in a vessel. (You cannot measure quantity except gravimetrically -- and you are already doing that -- why the double check on the same data? Are you expect the water in your vessel to vary from the know standard?

Here is your switch though. You don't need an Arduino -- and it is consistent with the project definition that you have provided so far.

Now as for the weighing -- I posted a simple application framework in this section that should get you started in programming.

This looks like a High School project and you want us to do your home work. That's fair enough -- some people love to help with those projects.

Maybe you should tell us what this is about and people are likely to be more sympathetic.

PS: Do you know how to be safe with hydrogen? Is this a supervised project? You do know about explosives -- right?

You do realize that you will supply more energy than you retrieve from the process -- right?

5

OK here is a clearer explanation of what I am trying to achieve.

Firstly I want to dehumidify the air into water (or ice in this case). To do this I am using a peltier element. I will need to be able to switch this element on and off via the Arduino (hence the need for a programmable switch). I will need to measure the weight to know when the peltier has collected enough ice to be turned to water (switching the peltier off will immediately cause the ice to heat up and fall into the water collection tank.

Secondly, I want to convert the water to oxygen and hydrogen via electrolysis, I will need to measure the water level to make sure their is enough water to submerge the electrolytes (hence the measuring of water levels), and I will need to be able to switch the electrolytic process on and off (hence the need for a programmable switch).

My reason for doing this is "just because".

Well, all this kind of depends on whether you're doing this on an industrial scale (with industrial explosive atmosphere considerations), or at the kitchen sink with some old coffee jars.

I am not doing this on an industrial scale.

This depends upon the voltage and current of the electrolysis process. Or are you asking about how to do the actual electrolysis?

I am clearly not asking how to do the actual electrolysis, all I want to do is turn the process on and off via the Arduino. Voltage is 7.2 and current should be 500 mA (though I am open to the current varying to another up to 3A).

Same as above: what did you have in mind? My guess is that it's low-voltage high-current DC in which case a MOSFET would work, or a relay.

Peltier draws 3A from 10V of DC.

What kind of weight difference are you looking for? A change of a few grams, hundreds of grams?

A few grams.

This looks like a High School project and you want us to do your home work. That's fair enough -- some people love to help with those projects.

It is not a High School project.

PS: Do you know how to be safe with hydrogen? Is this a supervised project? You do know about explosives -- right?

I know how to be safe with hydrogen.

You do realize that you will supply more energy than you retrieve from the process -- right?

Yes.

6

For switches you probably use logic level mosfets or solid state relays. There probably a lot of alternative methods for measuring humidity from a horse hair contraction/expansion to various electronics. As to the ice on the peltier you might look at an optical way to detrmine frost buildup. As to some of the other off the wall comments and concerns like "You do realize that you will supply more energy than you retrieve from the process -- right?", well, they mean well. :wink:

7

Switching power from Arduino: some possibilities here: (OK, that search didn't work!!!)

FET Switches: http://arduino-direct.com/sunshop/index.php?l=product_detail&p=60

Relay Boards: =relay&s[title]=Y&s[short_desc]=Y&s[full_desc]=Y&s[sku]=Y&s[match]=all&s[cid]=0]http://arduino-direct.com/sunshop/index.php?l=search_list&s[search]=relay&s[title]=Y&s[short_desc]=Y&s[full_desc]=Y&s[sku]=Y&s[match]=all&s[cid]=0

Hope that works.. Sorry!

DISCLAIMER: I mentioned stuff from my own Shop...

8

Terry what search criteria did you use?

9

Narwhal:
Terry what search criteria did you use?

Sorry! I redid it differently.

10

Is there a manual for that FET switch? Or is it one of those things that are fairly standard to operate? If so is there a tutorial on this?

As to the ice on the peltier you might look at an optical way to detrmine frost buildup

Can the Arduino perform such image analysis? I'm looking to make this totally Arduino based so a camera to a desktop is a bit of a no go. I am open to other ideas however.

11

zoomkat:
For switches you probably use logic level mosfets or solid state relays. There probably a lot of alternative methods for measuring humidity from a horse hair contraction/expansion to various electronics. As to the ice on the peltier you might look at an optical way to detrmine frost buildup. As to some of the other off the wall comments and concerns like "You do realize that you will supply more energy than you retrieve from the process -- right?", well, they mean well. :wink:

Yes we do -- at least I do. Or I try.... not always successfully... :roll_eyes:

There are an awful lot of ill defined projects that appear here. The process to help and provide references is baffling since people don't always make it clear what they are looking for.

If it is a student project we should be a lot more patient and understanding of the need to spell out the basics. ...but not willing to do a homework assignment..

Also -- there are often many solutions to the problems presented -- but not knowing the abilities of the person requesting the help makes it difficult to help sometimes.

People can give more information -- or less as they please -- but then people reading the request have to guess how to help. Then it's like pulling hen's teeth.

BTW: Here is a useful Refernce for people building add-on circuits.
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=Electronic+Circuits+Graf&x=0&y=0

Check out Volume Three for example...

\Not sure if it is the best reference.

The books by Graf are excellent resources for explaining the questions of FET's and MOSfets etc...

In this case whether it is an NPN power transistor or a FET style Semiconductor is a non-issue in my mind -- the only question is -- can it pull the current to run the device you want operated, and can you supply a signal sufficiently strong to "saturate" the semiconductor device.

If you don't really understand the electronics side -- just buy commercial products which promise to do what you want. It's definitely faster and more certain -- even if a touch more expensive.

12

Can the Arduino perform such image analysis? I'm looking to make this totally Arduino based so a camera to a desktop is a bit of a no go. I am open to other ideas however.

Optical and image are not really th same thing. There are little optical devices like below used in bots for distance and line detection that might be of use. If you have a dark place on your cooler (possibly colored by a black sharpie), then this gizmo might detect when the spot starts becomming lighter from frost buildup.

http://www.lynxmotion.com/p-58-single-line-detector.aspx
http://www.lynxmotion.com/p-260-sharp-gp2d12-ir-sensor.aspx

13

That's an interesting thought, I will try painting on of the peltier elements black and giving it a go with the single line detector, however a problem looms, the Peltier element's cold side will be facing the ground (so when it turns off the water will melt into the collection vessel), so to detect ice the single line detector would have to be below it, and would be subjected to a downpour of water. I'm not sure if I can waterproof this because I assume any lense I put around it will alter the IR signal.

14

Narwhal:
Is there a manual for that FET switch? Or is it one of those things that are fairly standard to operate? If so is there a tutorial on this?

http://arduino-info.wikispaces.com/Brick-4ChannelPowerFetSwitch

15

Not sure what your overall objective is, but you may want to design with the intent that the water is removed from the surface as it condenses and not allow it to freeze on the surface.

16

So after some further research, it seems what I am looking for is a solid state relay. However all the ones I found are rated for AC, when I need to relay a DC circuit. Any ideas where to get one that works for a DC circuit?

17

zoomkat:
Not sure what your overall objective is, but you may want to design with the intent that the water is removed from the surface as it condenses and not allow it to freeze on the surface.

I would agree with this, since I built something almost exactly like what you are doing. I had a peltier cooler hung with a heatsink on it so that it would drip over a funnel with a small hole into a reservoir. This was with a 60 watt cooler and due to the constant flow of water, it would not freeze.

It would collect about 1/4 cup in 2 hours in my 90deg 90% humidity garage.

This would simplify your project a bit. The addition of a small fan would also help prevent freezing on a more powerful unit, as would a larger heatsink.

Also, if you don't freeze it and use a fan to circulate the air, you can route the excess cold air from the cold surface to the hot side, making it more efficient.