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16  Using Arduino / General Electronics / Re: Electric water/pipe valve? on: March 16, 2011, 10:56:02 pm
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Alternatively have you considered simply turning off the pump

Turning off the pump unfortunately will allow water to trickle back through the pump.

Use a check-valve (you make one for a few cents). 
Or use a different kind of pump that prevents back- (or forward) flow.
The combination of a low-performance pump and an electrically-operated valve is going to be difficult to resolve.

Aye I agree. I'm gonna abandon the water pump idea and try the motors with the threaded rods instead. Thanks for replying smiley
17  Using Arduino / General Electronics / Re: Electric water/pipe valve? on: March 16, 2011, 04:08:58 pm
Attached is a quick drawing of the general idea.

As the rod turns the nut moves up (or down) and moves the panel with it.

Note that there are three pivot points (the red dots), obviously the panel, but also the motor and the nut have to pivot as well. This means that both the motor and the nut have to be in a mount of some kind that allow them to pivot. Pretty easy to do.

This is essentially a "linear actuator" done on the cheap.

This can be mounted several ways and may have to be different depending on the clearances, but this was quick to draw.

Another thing to think about is the need to rack in two axis. One of them (the altitude?) only changes over weeks and months an dit's not normally worth the effort to dedicate control gear to that. Either leave the whole apparatus at the optimal angle for you latitude or have a manual system that you adjust every few weeks.

Another thing to think about, you will need an RTC or some method of knowing the time/date etc.
______
Rob


Why would need an RTC? Isn't the point of having a solar tracker so you set it and forget it?

I've been thinking that it probably isn't worth the extra effort to make it pivot on the second axis. But I thought for a challenge it might be fun, because eventually I want to create a solar parabolic stirling generator and that requires the 2 axis tracking style system.

Thank you very much for the diagram! It certainly helped me make sense of it all. I suppose I could get an electric motor that has a threaded drive shaft off of it and I could use some hardware to bolt them together. But how do you attack a metal nut to a piece of wood? I could see me screwing a piece of metal to it and maybe welding it? But then again it has to pivot right ... Hrm...
18  Using Arduino / General Electronics / Re: Electric water/pipe valve? on: March 16, 2011, 06:38:56 am
Threaded rod (aka allthread) is just a very long bolt, if you put a nut on it and turn the rod the nut moves linearly along the rod.

So by mounting the nut to the thing that needs moving and turning the rod the "thing" moves.

So it's just a matter of mounting things in the right place.

It may help if you tell us what needs to be moved.

______
Rob


The object needing to be moved is a passive solar heater. Basically a big wooden rectangular flat box, with a bunch of aluminum painted black inside that absorbs heat from the sun.

So how would I attach the metal threaded bolt to a motor? If I wanted the solar heater to move on two different axis's would I need two motors? How about attaching the nut to the panel? Any tips with that? Thanks for the advice man! I really appreciate it. My official project thread is over here http://arduino.cc/forum/index.php/topic,54992.0.html
19  Using Arduino / General Electronics / Re: Electric water/pipe valve? on: March 15, 2011, 09:31:35 pm
I can see at least one problem with this approach, what they call "sticktion".

In other words it takes more energy to start something because it's "settled" in one place and the grease, dirt, general friction etc takes effort to overcome. Once it is overcome things run more freely.

So the problem is you pump water until it starts moving, then it moves too fast and you have to pump back again. If you pump too much back it may stop and you're back to square one. Don't pump fast enough and the thing runs away, pump too fast and it goes the other way.

This assumes that you have feedback and actually know what directing things are pointing. Even if it works perfectly you still need feedback.

If the above happens I doubt your pump will be able to move water fast enough to stop it, so the panel (or whatever it is) will slam to the end position.

If this is a panel or something with a large surface area then it will be subject to wind loading and once again without feedback you won't know it's moved. By definition the system is well balanced so therefore easily upset by wind, a bird or just about anything.

All in all I think you're cruisin' for a bruisin' with this approach, an object sitting on a CV is inherently unstable, once it gets just a tad out of balance it will take off and your system doesn't sound like it will have the response time to correct problems.

EDIT: If you just want to follow the sun you can usually do that with a motor, some threaded rod and a nut (for one axis admittedly, double for two). Very cheap.
______
Rob



I think you are correct. Can you explain this rod/nut motor thing? I have troubles visualizing stuff with out an image. I have a fairly strong programming background, but I'm kind of weak when it comes to physical engineering. I hope to improve smiley-grin
20  Using Arduino / General Electronics / Re: Transistors? on: March 15, 2011, 05:17:22 pm
Well a relay is an all on or all off device. Where as a transistor can continuously  control a flow of current from a much smaller one.
Think of it as a valve, a small turn controls a lot of flow.

Ok, I'm getting there slowly. So the Transistor doesn't really amplify a current. It just has the ability to allow the current to reach it's maximum potential? It's not generating power from somewhere is it?
21  Using Arduino / General Electronics / Re: Transistors? on: March 15, 2011, 03:56:00 pm
Quote
a transistor changes the voltage/amperage of a current?

No a transistor is like a valve, a small current flow in the base makes a larger current flow in the collector / emitter.
The ratio of these two currents is the gain. o for example if you have 2mA flowing in the base with a transistor that has a gain of 80 there will be 2 * 80 = 160mA flowing in the collector providing the resistances around the rest of the circuit allow that much to flow.

That makes sense! So it's kind of like a relay with no moving parts?
22  Using Arduino / General Electronics / Re: Making commercial cell phone on: March 15, 2011, 03:52:24 pm
Hi!
Thank you for quick reply. I absolutely agree with you. so many cell phone companies, lot of complex designs to make it competent in current day mobile market.

But, what If I want to make a fixed-cellphone? something like this,
1. which is always connected to electricity(maybe with a 2hours battery charging) using normal cellphone charger kind of.
2. size does not matter(compared to current compact models)
3. No other features except redirecting mic input to modem and voice from modem to speaker, no lcd = no separate application processor, memory etc needed?

In nutshell, putting arduino+gsmshield+speaker+battery(backup) in a custom designed case (like arduino case) and connect it to power using mobile charger.
And, what the user have with him is "JUST a gsm network" and what he wants to do is "just hear and talk when others call him" using that box.

And regarding regulatory approvals; doesnt these readymade modems from Telit,Seimens etc have those approvals covered already?  at least those data sheets talk a lot of many approval covered?

I ABSOLUTELY value and trust every point you mentioned. All I am trying is to get things clarified more.


Thank you once again
Naveen



That would be a very strange cell phone indeed. I'm not an Arduino master by any means, but I think even the fastest Arduino might have troubles processing voice in real time. I think the fastest ones don't even break 20mhz on the clock. I could be mistaken though.
23  Using Arduino / General Electronics / Re: Electric water/pipe valve? on: March 15, 2011, 03:49:10 pm
If you want a low pressure "solenoid valve" then go for a motorised central heating zone valve.  These operate from mains AC but more importantly are readily available and reasonably cheap.  In fact you should be able to find one at your local scrap dealer for pennies.

Alternatively have you considered simply turning off the pump

Thanks, I'll google those and see what I come up with. I have a friend who works with Heat Pumps, perhaps I should ask him.

Turning off the pump unfortunately will allow water to trickle back through the pump.
24  Using Arduino / General Electronics / Re: Electric water/pipe valve? on: March 15, 2011, 03:47:36 pm
I've seen a lot of thread on this and other forums where people wanted a cheap low-pressure valve.

I have yet to see anyone actually find one. If they did they didn't report the fact.

There have been all sorts of methods proposed to bodge something up, but nothing I've seen that's reasonable. One of the problems is that ball valves require a huge amount of torque to turn them

OTOH if you are pumping and there is no pressure when you stop then you can just turn off the pump and have a non-return (or check) valve.

What's the exact application?

______
Rob
  

Basically I'm building a water ballast tank. Which is used to control positioning. Ahem, I refer to it as poor mans hydraulics. I want a fairly heavy object to face the sun during the day time. So my plan was to use 2 axis positioning by having counter weights perpendicular to each other (the object is a large rectangle pivoting on a CV Knuckle looking object in the center of the back of the rectangle). On the opposite sides of the weights, I would have containers that could hold water. I would use multiple photo resistors to track where the sun is, and according to a difference in readings from the sensors I would turn a pump, and open 1 of 2 valves to fill either of the tanks (or drain them back through the pump) to match the counter-weight.

I realize it's all possible with servo's and motors but I'm pretty limited for this project financially and I figured big servos and motors to move such a big object would be expensive and I also don't require the speed of a servo/motor. The sun doesn't change position very fast. The system also needs to be able to with medium wind speeds. I figured the ballast-counter-weight system might allow it to wiggle here and there.
25  Using Arduino / Project Guidance / Re: My First Arduino Project: Autonomous Solar Heat Controller on: March 15, 2011, 03:41:12 pm
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Is it similar to controlling a Shift Register Chip?

Much easier than that. You just set pins to be on / off using:

Code:
digitalWrite(pin, HIGH);
digitalWrite(pin, LOW);

Each relay will have its own pin. Unused Arduino pins can be used by your other parts.

Snoof! I'm still unsure of how that Shift Register works. Thanks for replying man.
26  Using Arduino / Project Guidance / Re: My First Arduino Project: Autonomous Solar Heat Controller on: March 15, 2011, 06:48:31 am
Hi,

It would, but you could not drive it directly from an Arduino pin, it would draw too much current. You would have to use a transistor.

You could use a relay shield like this: http://www.robotshop.com/seeedstudio-arduino-relay-shield.html

The relays will cope with 5A at 240V so probably more at 120V. Even if 5A at 120V, that would let you switch 600W.


I'm just starting to realize just how versatile this little microcomputer really is. How would I write code to control a shield like that? Is it similar to controlling a Shift Register Chip? Using 3 pins to control many?
27  Using Arduino / General Electronics / Re: Electric water/pipe valve? on: March 15, 2011, 06:46:55 am
Quite often pond pumps are centrifugal pumps which don't always need to be closed when turned off.
Turned on they pump water up, once you cut the power gravity will let the water above the pump flow back through the pump into the reservoir.

Yes, I can attest to this. I do not want the water to flow back through.

If I must use a relay that is ok. I just thought I'd check and see.
28  Using Arduino / General Electronics / Re: Transistors? on: March 15, 2011, 06:21:41 am

Yea I got about half way through it before it went over my head.
29  Using Arduino / General Electronics / Re: Electric water/pipe valve? on: March 15, 2011, 06:16:52 am
More information required :

a) temperature of water
b) pressure across valve when closed
c) flow rate through valve when open
d) power supply used to operate valve (low voltage 6/12/24DC or mains 110/230AC)



Above freezing, less than 30C.
Very little pressure. Maybe 2 psi tops.
A little pond pump. Maybe 50gallons per hour.
If possible, 5vDC or whatever I can get the arduino to max out at with out using a relay.
30  Using Arduino / Project Guidance / Re: My First Arduino Project: Autonomous Solar Heat Controller on: March 15, 2011, 05:57:17 am
http://canada.newark.com/tyco-electronics-potter-brumfield/t9as1d12-5/power-relay-spst-no-5vdc-30a-pc/dp/26M8314 Would the Arduino be able to use this to switch 120v power?
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