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Driving a latching valve

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That' s ton of horsepower (PIC + H bridge) to control one very small latching valve (5.5mW-sec to latch).

May I ask what the application is? This might help in deriving a solution.
 
Yes. I am developping a device to monitor infant sucking. I need to integrate in the baby bottle a valve (small as possibile) in order to let air flows from the outside to the inside of the bottle when a 25 or more kPA depression is created in the chamber.
I have a pressure sensore MPXV705 that monitors the pressure inside the bottle. The analog signal provided by the sensor in converted with ADC MAX1238 and sent to PIC with I2C interface, so then then PIC sends the datas to PC with RS232.
What i would like to do is to control the valve with the PIC so that, once the pressure i read from the sensor reaches the negative limit pressure, i want to open the valve so to make air flows inside and rehestabilish atmosferic pressure.
I need to do this not just one time, but everytime the pressure reaches that value, so i need like the valve to open/close lots of times.
 
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Excuse me , I have also found this other valve **broken link removed** this is a Classical Solenorid Valve that will close once a rated voltage is applied to it. Will i need to use a driving circuit also fo r this kind of valve? or can i use something like this?
**broken link removed**
My questions so are :
1) will this last circuit work for making the PIC drive the valve i just sent you the link?
2) can i simply turn on/ off the valve with this circuit with a simple output_high(),output_low() command from the PIC?

I know mines are lots of questions but im really new in all this!!

Thank you so much
 
Your attachment isn't working.

But, that aside, the PIC (by itself) can not supply the power needed to hold the solenoid you've listed.

<EDIT>: Seems like, though, you could accomplish this with a simpler pressure sensor controlling a valve system.
 
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I have seen this tutorial on how drive solenoids so in the attachment there was something like this showed in the tutorial. The differcen its the valve has a different operative voltage.

https://www.embeddedrelated.com/showarticle/77.php

The PND Valve solenoid i sent you the link can be made to work with 3 V operating voltage. That could be done by the PIC isnt it?or am i missing something?
 
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The PND Valve solenoid i sent you the link can be made to work with 3 V operating voltage. That could be done by the PIC isnt it?
That link doesn't disclose the current the solenoid needs. The PIC can provide only a small current, so you will probably need a transistor or driver IC to interface the PIC to the valve.
 
thank you can you suggest me any IC or transistor configuration to use? how should I use it in my schematic?
 
...I need to integrate in the baby bottle a valve (small as possibile) in order to let air flows from the outside to the inside of the bottle when a 25 or more kPA depression is created in the chamber...
Wouldn´t a simple one-way valve be a more elegant solution?
 
I agree with Kubeek. A simple mechanical valve (e.g. thin elastomer tube covering an aperture in a closed-end metal tube, like an old-style bike tyre valve) would surely do; unless you have a particular reason for wanting an electro-valve?

Edit: If you must use an electro-valve then an interface as below would probably suit. Component values would depend on the current requirement of the valve.
View attachment 66943
 
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Hello!!! Thank you for your reply! Yes i must use an electro-valve because i need to control it with a PIC ..... I was actually wanting to use a circuit like that one you showed me. But will it be allright with the solenoid valve i showed before?
**broken link removed**

The valve will be closed if a 3 V is applied so i would like to know with the circuit you told me can i drive the valve on and off simply commanding the PIC pin with output_high and output_low commands?

Thank you so much!!!
 
The valve will be closed if a 3 V is applied so i would like to know with the circuit you told me can i drive the valve on and off simply commanding the PIC pin with output_high and output_low commands?
(My emphasis)

At 3VDC, the solenoid will draw 167mA (0.5W/5VDC=0.167A).

The circuit provided by alec_t, can be triggered by the PIC and, with an adequate 3VDC supply, will easily carry that load.

By "Adequate 3VDC supply" I mean a 3VDC supply that can provide the current you require (167mA) AND maintain its 3VDC output (no voltage sag).
 
Ok so you are saying the circuit will work well unless i got a really good battery for power supply??? Did I understand correctly?

Thanks to everyone for the wise comments and help I am very dummy in this field and learning step by step!
 
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Ok so you are saying the circuit will work well unless i got a really good battery for power supply??? Did I understand correctly?

Thanks to everyone for the wise comments and help I am very dummy in this field and learning step by step!

Your use of the word "unless" has me confused.

Nonetheless, what I am saying is that, yes, the circuit will work so long as you have a good battery (power supply) which can maintain a 3VDC output from the circuit alec_t provided, i.e., not let the output drop below 3VDC when triggered by the PIC to do so.
 
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Sorry for my English...I am not a native speaker and my mind really jamming on this project that no space for focusing on the grammar! LOL!

Ok So I need to find a proper battery or power supply.... Any suggestion on batteries I should look for ?
 
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Here it is my stupid question:


can't I use two different supplies for the PIC and the solenoid?

Like just for powering the solenoid couldn't i use a battery like this one: https://www.sparkfun.com/products/341

and then power the PIC separately lets say with another battery or with some wires?

or this thing its impossible to do?

Sorry for stupid questions and thanks for help
 
At 3VDC, the solenoid will draw 167mA (0.5W/5VDC=0.167A)
At that current the circuit I posted may not be adequate, as it would require considerable base current.
Here is a modification which should cope better and be less demanding on the PIC's output current capability.
View attachment 66946
can't I use two different supplies for the PIC and the solenoid?
That is not a stupid question; it is very sensible. It would indeed be better to have separate supplies, because heavy inductive loads could disturb the PIC's supply voltage and cause glitches. Also, you could run the PIC at 3V and would be able to use, say, a 6V supply for a different valve if you couldn't source a 3V one.
However, if you do use a single supply then make sure to have plenty of supply decoupling capacitance (e.g. 100μF or more connected across the supply, and 100nF connected across the PIC supply pins very close to the PIC).
 
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Ok thank you so much!!!! Really thank you for your help!!! I will consider everything you told me today and tomorrow start back thinking and collecting the main ideas for this project! If I will have other doubts/questions I will post here back again!!

Thank you so much,
Maria
 
Maria,

Ok. I've re-read your 3rd post. I think I have a better picture of what you are trying to do.

Since this involves infants, I would first check for your local and/or federal laws concerning electronics and infant safety.

That said, the power supply you choose would have to meet the requirements laid out by the appropriate authority from a safety stand point.

Having done that, and NOT knowing your total power (Amps times Volts) requirements, I'd suggest using a combination of "D" cells, 2 in series (to provide 3 VDC) for starters, and then monitor how long they last before the solenoid no longer operates satisfactorily.

There's a lot more to this question you ask then you may realize. But, given that there's the assumption that the solenoid (valve) will only operate momentarily (to relieve the baby bottle pressure differential) and only every so often, I would think this battery arrangement should last a good while.

Can't know for sure, however, with no more information than is at hand for now.

With a tip of the hat to alec_t, here's a simulated circuit you might use that has the solenoid, etc., parameters you've given PLUS an isolated ground recommendation that, I hope, would meet any electrical safety issues.

<EDIT>: (I'll be honest: don't exactly know how to accomplish this isolation. Going to look into it.)

View attachment 66947 View attachment 66948
 
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Maria,

Ok. I've re-read your 3rd post. I think I have a better picture of what you are trying to do.

Since this involves infants, I would first check for your local and/or federal laws concerning electronics and infant safety.

That said, the power supply you choose would have to meet the requirements laid out by the appropriate authority from a safety stand point.

Having done that, and NOT knowing your total power (Amps times Volts) requirements, I'd suggest using a combination of "D" cells, 2 in series (to provide 3 VDC) for starters, and then monitor how long they last before the solenoid no longer operates satisfactorily.

There's a lot more to this question you ask then you may realize. But, given that there's the assumption that the solenoid (valve) will only operate momentarily (to relieve the baby bottle pressure differential) and only every so often, I would think this battery arrangement should last a good while.

Can't know for sure, however, with no more information than is at hand for now.

With a tip of the hat to alec_t, here's a simulated circuit you might use that has the solenoid, etc., parameters you've given PLUS an isolated ground recommendation that, I hope, would meet any electrical safety issues.

<EDIT>: (I'll be honest: don't exactly know how to accomplish this isolation. Going to look into it.)

View attachment 66947 View attachment 66948

Thanks for your reply! I think i will surely need some good supply because the problem now is that the valve i showed you till now its a Normally Open valve that will close once powered. and In my application I need the valve to be in NC condition and then open at command to let air enter inside the bottle. So you think all of this will work the same?
However tomorrow i will have to contact the seller to ask about even other products so it is very possible for me to find a similar valve NC, that will surely be controlled with less power troubles.

For what concern the safety regulations and all : I am now starting some basilar design of the device that is still in the way of testing so for the legal and country-rules point of view there is still time and It won't be my duty do check on this but others will do it when the time will come..however thank you for the hint!

About my circuit i would like to create the following:
1 PIC18F46J50 (it operates at 3.3V but has some pins 5.5V tolerant)
2 pressure sensors MPXV7025 of the Freescale Semiconductor: these are analogic sensor powered at 5V
1 ADC converter MAX1238 that takes signals from sensors and send the datas of pressure into the bottle to the PIC through I2C

and then the valve , possibily of the kind we were discussing for. The PIC is suppose to communicate with RS232 and send data to PC.

As u see the full scheme is really simple i am just very concerned on how to deal with the valve. One pressure sensor measure continously the pressure into the baby bottle and i would like to use its measure as a trigger value to control the opening of the valve so that when a depression is created into the bottle,the valve will let air flows inside.

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?

Thank you so much for your help and interesting advice.

Tomorrow i will post back with news
 
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