Driving a latching valve

[alec_t]

About the supply with these above components would it be ok to consider:
1) a 5V supply for the sensors and then with voltage regulator going down to 3V for powering the PIC?
2) using a separate battery just and only for the valve?

That should be ok. All subject to the above-mentioned safety requirements, of course. But I still don't see why you can't use a simple non-electric valve, which would automatically open when the bottle pressure dropped. Or are you trying to control the valve and so control/measure the amount of liquid the infant drinks?

 

[alimary15]

That should be ok. All subject to the above-mentioned safety requirements, of course. But I still don't see why you can't use a simple non-electric valve, which would automatically open when the bottle pressure dropped. Or are you trying to control the valve and so control/measure the amount of liquid the infant drinks?

hello,thanks for your reply!
I dont know much about valves since the first time I am up to use them....talking about a mechanical valve ,what I am trying to accomplish is the following:
I need the valve to remain closed while the baby is sucking the milk from the baby bottle.so that when he drinks milk a vacuum in created in the bottle. I am measuring this negative pressure with a pressure sensor.I need during this time the valve to remain closed and just when the vacuum is greater then 2-3 PSI I need the valve to open to let air enter.
The thing is I need some vacuum to be created in the bottle and I just must a let air flows inside (so to return to atm pressure) when the vacuum is too big for the baby to deal with.


SAid this my question is :is there any mechanical valve that can open just for Pressures more than the 2 psi??
I honestly didn't find any but propably I didn't look for it correctly.

All I saw were propotional valves but they can't work for me cause they allow air enters proportionally to differential of pressure but in my case I need the vacuum to be created in the bottle but this vacuum must range till 2-3 psi.
In summary I do not want the air to eneter for vacuum less than 2-3 psi.

So is there a mech valve can do this? Can you help me identify it?because I didn't find anything

Thanks

 

[alec_t]

You could easily make one. All you need is an apertured enclosure with a diaphragm over the aperture and a light spring (force adjusted to suit 2psi pressure on the diaphragm) pushing the diaphragm to seal off the aperture.

Here's the sort of thing
View attachment 66956

That won't let the air return to atmospheric pressure, though. It will stay at 2-3psi below, until the baby releases the bottle teat.

 

[cowboybob]

About my circuit i would like to create the following:
1 PIC18F46J50 (it operates at 3.3V but has some pins 5.5V tolerant)

The PIC will operate with as little as 2.0 VDC.

2 pressure sensors MPXV7025 of the Freescale Semiconductor: these are analogic sensor powered at 5V

Fine (get the differential model). Although you might want to consider a mechanical buffer (diaphragm) of some sort to keep moisture away from the pressure sensor face.

1 ADC converter MAX1238 that takes signals from sensors and send the datas of pressure into the bottle to the PIC through I2C

Not necessary. The PIC18F46J50 has built-in (multiplexed) A/D converters. You will, however, have to use a resistive voltage divider network to scale the output of the MPXV7025 to, for instance, a 0 - 3.0VDC range. Not a big deal.

and then the valve...

Fine. That's covered.

The PIC is suppose to communicate with RS232 and send data to PC.

The PIC18F46J50 also has a USD 2.0 interface, which I would prefer using. The RS-232 and RS-485 serial comms are more difficult to work with.

I'm assuming you have access to a PIC programmer.

Just some thoughts.

 

[alimary15]

The PIC will operate with as little as 2.0 VDC.



Fine (get the differential model). Although you might want to consider a mechanical buffer (diaphragm) of some sort to keep moisture away from the pressure sensor face.



Not necessary. The PIC18F46J50 has built-in (multiplexed) A/D converters. You will, however, have to use a resistive voltage divider network to scale the output of the MPXV7025 to, for instance, a 0 - 3.0VDC range. Not a big deal.



Fine. That's covered.



The PIC18F46J50 also has a USD 2.0 interface, which I would prefer using. The RS-232 and RS-485 serial comms are more difficult to work with.

I'm assuming you have access to a PIC programmer.

Just some thoughts.

Yes I have access to the Pic programmer and I have already developped the electronics for taking the signals...about the valve... I was looking into something of this kind
**broken link removed**

do you think will it be good??? they have the cracking pressure i need of 1 PSI and they simply mechanical valves. Can you give to them a look?

thanks

 

[alec_t]

That valve looks good for your purpose, and being all plastic/stainless should be easy to sterilise too if need be.

 

[cowboybob]

...about the valve... I was looking into something of this kind
**broken link removed**

...do you think will it be good??? they have the cracking pressure i need of 1 PSI and they simply mechanical valves. Can you give to them a look?

Check valves of this sort can be customized to all manner of "cracking" pressures so, yes, it would work, but with this understanding:

There would always be some very low level of vacuum in the bottle (somewhat lower than whatever the cracking pressure is set to) and that may or may not be problematic for you.

It sure would simplify things, though.

 

[dr pepper]

Have you considered an approach similar to a peristaltic pump?
Use a length of neoprene tube (you could make the entire tube run one piece of neoprene), and then use an rc servo or a solenoid with a suitable attatchment to pinch the pipe off and stop flow.
This kind of valve would have an extremely low cracking pressure (just the restriction of a length of tube), is flow wise very simple and all the fluid/air handling part can be replaced in seconds for very little.

 

[alimary15]

No i have actually never considered this ...but thanks for the idea!!! Actually I would like to keep the design as simpler as possible and maybe creating some sort of device that can be easily portable with few energy consumption. So yes this can be an idea but I think the best would be just using a mech valve with no additional need to control

 

[alimary15]

Check valves of this sort can be customized to all manner of "cracking" pressures so, yes, it would work, but with this understanding:

There would always be some very low level of vacuum in the bottle (somewhat lower than whatever the cracking pressure is set to) and that may or may not be problematic for you.

It sure would simplify things, though.

Yes , I have actually managed to find these valves with a cracking pressure of 1 psi and then I even managed to get some samples from www.smartproducts.com of their miniature check valve part #101 that has a cracking pressure of 1.43 psi. This range of cracking pressure is perfect for my application and yes, I would always accept vacuum to be created into the bottle, I just don't want it to be bigger than 1-1.43 psi ,because these values of vacuum are of the same kind the baby is able to create in his mouth when suckign to get the milk from the bottle so if the vacuum it is too big it will really be an obstacle for the baby to get the milk!!!
I really thank you for your tech and useful advices!!!!