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bailout
11-09-2006, 02:10 PM
Hey all, this is my first post here, however I've been playing with stamps since before the BS2 =). Heres the question:

I have a solution of water and electrolyte (NaOH if you care) charged with 12 volts (its an electrolyzer for hydrogen). I want to detect the water level in one of the cells with screws through PVC pipe


Heres what i've thought up.... (attached)

Am I in the right direction? Should there be more resistors in there or something, perhaps a diode on the screw. (i'm from the school of... what the heck do resistors do?) haha. Yea, I'm still learning

My main concern is not to burn up my stamp =)

Loopy Byteloose
11-09-2006, 04:13 PM
There are really two fundamental approaches with subsets.

1. In contact with the solution
a. a float switch
b. a conductive sensor
2. Not in contact with the solution
a. ultrasonic distance
b. IR distance

I am sure we can come up with many more ways to do this, but it really all comes back to what purpose the informaton needs to serve, how dangerous is contact with the solution, and what physical limitations exist.

In regards to your design, I wonder why you bother with +12volts and a +5 volt regulator when you already have +5 regulated available on your BasicStamp.

I also wonder why you would get the physical level of the fluid involved with its electrical activity. That makes things more complex as I guess the 4volt potential might change and provide false information.

In other words, I would go with a float device and mechanical switches if at all possible. Electrical isolation and hazard isolation are both useful. Consider a small capsule that floats a top the liquid. Have it attached to a rod on its top-side. Have the rod pass through the top of the liquid's housing. And have it directly or by lever arm, throw a micro-switch.

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Shawn Lowe
11-10-2006, 02:50 AM
You might want to consider a wires on the outside that are close together. Then you can use the capacitance of the liquid level to change the frequency of a 555 circuit, and check that with the stamp. I saw this on the kronos robots website, and it seemed like a smart idea.

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Shawn Lowe


My last words shall be - "NOT YET!!!"

bailout
11-10-2006, 03:10 AM
Ok, the +12v is from the car battery.· and the ~4 is after the +12v has gone through the electrolyzer.· Yes, that will change slighty here and there, but thats why i have the PNP, i'm hoping that anything from 3-12V will be enough for the gate of the transistor to get at least 5v of that 12 to the regulator (seeing as how i really only need like 1.5 for the BS to see it as HIGH.· As for the mechanical side of it, this unit is sealed and at 200+psi, and its already electrically charged, so i figured I would use that to my advantage.· Basicaly, when the water level is up, the unit turns on, when its down, it turns off.· And like i said, it already has the electric charge because its a hydrogen electrolyzer.· Hopefully i'll be testing this tomorrow, and i just wanted to make sure i'm not going to fry anything.



Thanks all,

Jason

PS... if you're interested, heres some uhh "test" videos =)

http://www.youtube.com/watch?v=8EFFjNS0i2A (http://www.youtube.com/watch?v=8EFFjNS0i2A)· Round 1

http://www.youtube.com/watch?v=FkwLLbshUlg (http://www.youtube.com/watch?v=FkwLLbshUlg)· Round 2
Yes, we're a bunch of rednecks =)

Tommy Bot
11-10-2006, 03:13 AM
Is the cell air tight?
You could use a pressure transducer with setpoint contacts or an A/D converter.

What is the cell material?
If it is some type of plastic, you can use an external capacitance type sensor as a digital input to the Stamp.
Or you can use one of the various types of trip beams, multiple sensors, multiple setpoints.

Are you only concerned with low level, or constant monitoring of level?
You can put your fuel cell on a load cell and use weight and an A/D converter

Is the casing opaque or translucient?
There are many ways to skin the cat...

Float switches are available fairly cheap that are encapsulated, the reed switch is sealed in the float and the wires are encased inside the tube which is has a threaded coupling for pass through of the lid.

More details, more options

Tommy

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Tommy, I know it wasn't designed to·x, but can you make it·do x·anyway?



Post Edited (Tommy Bot) : 11/9/2006 8:18:07 PM GMT

Tommy Bot
11-10-2006, 03:27 AM
Use your 4+ volts from the screw to hold down (for fail safe) (or make, if not an issue ) a solid state relay, use the dry contacts for your Stamp. Feed VSS to the hinge side of the contact, and N/O or N/C to the Stamp input.

200psi in PVC? what schedule, and size?

How is liquid expended used up, how is it replaced? Maanually or automatically?
Is there pressure relief?

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(Frequently heard from other's)

Tommy, I know it wasn't designed to·x, but can you make it·do x·anyway?

·

bailout
11-10-2006, 12:49 PM
Boy, i was looking for a quick and simple answer here, but I thank you all for your insight. =).

1st, yes 200psi in sch 40? 4" pvc (its rated for 200, i've had it to 250 (oops)

The water level is controlled by how much hydrogen is in the tank. When the tank gets full of H it will push the water down and i need it to shut off the electrolyzer (and/or open a relief valve). When the H gets low (water level high) I'll allow the solenoids to open and the H to go to the engine. Simple as that.

""Use your 4+ volts from the screw to hold down (for fail safe) (or make, if not an issue ) a solid state relay, use the dry contacts for your Stamp. Feed VSS to the hinge side of the contact, and N/O or N/C to the Stamp input.""

Thats what the transistor is for... I could be wrong, but wouldnt that have the same effect? The reason for the +12 is in case the voltage going to the gate is low (say 1-3 volts) I still need this thing to work. I figure with the right transistor, even with that 1-3 volts, it will 'open' the gate to let 3-5 volts through to make the BS2 read HIGH. Perhaps even another transistor on the other side of that regulator, switching the VSS like you were saying. Again... i do need this to work on a very low voltage, just incase.

Tommy Bot
11-10-2006, 08:42 PM
No you are correct, A transistor would be better. Someone else can recomend the proper transistor, that's not my strong suit. The voltage is adequate to bias the base of the proper transistor.

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(Frequently heard from other's)

Tommy, I know it wasn't designed to·x, but can you make it·do x·anyway?

·