Power Straw

RE: Power Straw

jw0752 — Sat, 12 Nov 2016 06:28:00 GMT

I found room on the existing board to add the [mention:193ac2434c814a24b46635a2210baec1:e9ed411860ed4f2ba0265705b8793d05] 3 part modification using a P Ch MOSFET, a 1 uF cap and a 220K resistor. Here are pictures of the modified circuit:

[View:/resized-image/__size/620x465/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-0e3b611e-6da6-4be4-8630-a1d5e0633cef/3823.contentimage_5F00_182762.jpg:620:465]

The IRF9520 in the upper right corner is the P Ch MOSFET and the capacitor is also pictured here. The resistor is mounted to the reverse side of the board.

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Sorry I remounted the board before I thought to take the picture. The resistor in question is in the lower right hand corner of the board. After modification the unit was tested and it dependably gave an approximate 1 second full voltage boost to the peristaltic pump before settling to the PWM setting. Now I can reinstall it into the test machine in Mom's room and see what the next bump in the road turns out to be. Once again thanks to Doug and Jan for their valuable recommendations that have made this improvement possible.

John

RE: Power Straw

jw0752 — Fri, 11 Nov 2016 07:16:05 GMT

Hi [mention:193ac2434c814a24b46635a2210baec1:e9ed411860ed4f2ba0265705b8793d05] & [mention:acaf6a9338de4eef8f6717d5561ed01d:e9ed411860ed4f2ba0265705b8793d05] ,

I have had a very fun night putting your two ideas on the bread board and experimenting with them. Here is the circuit and Schematic for the version inspired by Jan:

[View:/resized-image/__size/620x468/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-0e3b611e-6da6-4be4-8630-a1d5e0633cef/7144.contentimage_5F00_182756.bmp:620:468]

[View:/resized-image/__size/620x465/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-0e3b611e-6da6-4be4-8630-a1d5e0633cef/6562.contentimage_5F00_182757.jpg:620:465]

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This circuit worked very well. The resistors and capacitor used in the U3 comparator circuit produce approximately one second of full voltage to the peristaltic pump before dropping back to the level determined by the 555 PWM circuit. The prototype board on the left is my PWM Test Jig which I use to save having to bread board a PWM circuit every time I need one.

When I returned to the forum to post my experiences and success with the circuit inspired by [mention:acaf6a9338de4eef8f6717d5561ed01d:e9ed411860ed4f2ba0265705b8793d05] I was surprised to find another idea for this modification from [mention:193ac2434c814a24b46635a2210baec1:e9ed411860ed4f2ba0265705b8793d05] . This new Idea inspired me to return and also breadboard and test Doug's suggestion. Here is the revised schematic for Doug's solution as well as the pictures of the test set up.

[View:/resized-image/__size/620x468/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-0e3b611e-6da6-4be4-8630-a1d5e0633cef/6560.contentimage_5F00_182759.bmp:620:468]

[View:/resized-image/__size/620x465/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-0e3b611e-6da6-4be4-8630-a1d5e0633cef/3438.contentimage_5F00_182760.jpg:620:465]

[View:/resized-image/__size/620x465/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-0e3b611e-6da6-4be4-8630-a1d5e0633cef/2043.contentimage_5F00_182761.jpg:620:465]

I found this modification to work just as well and it produced approximately one second of full voltage on the peristaltic pump when I used 220K for the resistor in the RC circuit. I learned a lot from each of these approaches to solving the need to add a boost to the pump on start up when the PWM driver is below 100%.

Thanks John

RE: Power Straw

jw0752 — Sun, 06 Nov 2016 04:43:47 GMT

ERRATA :

I have discovered that I made a mistake and published incorrect information reference the mA draw of the peristaltic pump. If one looks closely at the picture of the Fluke Meter in my last post you will see that I had the meter set on mA AC. I do not usually use the Fluke to test mA and forgot that besides setting the function switch it is also necessary to push the orange mode button to switch from the default AC to DC mA. Experience and common sense should have triggered a "somethings wrong" warning in my head but it didn't until tonight. It is funny how often in my life I have made an obvious mistake and not realized it until a later time. Suddenly the realization just pops into my head that something isn't right. In this case a test using a meter set to mA gave a more common sense 300 mA draw.

John

RE: Power Straw

jw0752 — Sat, 05 Nov 2016 05:23:19 GMT

Here is the next iteration of the prototype using a peristaltic pump.

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The first thing to note is that the reservoir holder has been changed so that it will accommodate the standard drinking cup that is used in Mom's nursing home. Rather than messing with pouring the thickened water that she has to drink into a separate reservoir all the staff has to do is replace one cup with another and insert the red hose into the straw hole. I mentioned thickened water. I never realized this but if one is not able to swallow properly water of regular consistency can pose a greater danger of choking. For this reason they give Mom a special thickened water that is easier to swallow.

Here is a detail picture of the cup holder:

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The red hose from the cup goes to the inlet of the peristaltic pump. The pump itself is controlled by a variable pulse width modulation generator in the control box. I was very pleased with the small peristaltic pump as it is capable of moving 75 milliliter of the thickened water per minute when the pump is running at 12 volts. Since the control box (See Red Capped Knob on top of the control) allows me to control the PWM 0% to 100% I can reduce the output of the pump as needed so as not to over run Mom's ability to swallow. Here is a detail of the peristaltic pump and the manifold that I built to interface with the feed from the cup and the line to drinking tube.

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One of the very pleasant surprises was that the peristaltic pump only drew 32 mA at the full 100 % PMW level. This is more than a magnitude reduction from the 500 mA + current needed for the first prototype. Current calculations suggest that the battery should be able to run the unit for a couple weeks at a time without recharging. Since the Peristaltic pump pinches the line continuously there is also no need for a solenoid to prevent siphoning. Check out the ammeter reading for the pump.

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For the fun of it I made a video of the pump in action. Check it out.

[View:https://players.brightcove.net/1362235890001/NkxiVJdjx_default/index.html?videoId=5197675347001:740:466]

The unit is now back attached to Mom's wheel chair and she has been using it for a day. We will be watching for other problems and opportunities to improve it in the coming days.

John

RE: Power Straw

jc2048 — Thu, 03 Nov 2016 12:47:08 GMT

A good project - I admire you for using your practical skills like this to help someone you're close to.

That 555 has done you proud. A date code of 87 means it's almost thirty years old.

RE: Power Straw

jw0752 — Thu, 03 Nov 2016 06:22:38 GMT

I have begun the process to make improvements to the Power Straw. While I wait for the Peristaltic Pump, recommended by [mention:193ac2434c814a24b46635a2210baec1:e9ed411860ed4f2ba0265705b8793d05] , which should arrive in two days, I have busied myself redesigning the control box. I want to control the dosing rate of the peristaltic pump so that the proper amount of water can be dispensed. [mention:acaf6a9338de4eef8f6717d5561ed01d:e9ed411860ed4f2ba0265705b8793d05] had a good idea that I should use the LTC6992 voltage controlled PWM chip that I reviewed a couple weeks ago. I bread boarded this circuit last night and had it working very satisfactorily. Unfortunately the max voltage for the LTC6992 is 5.5 volts. Since I am running the Powered Straw from a 12 volt battery it was necessary to incorporate a 7805 regulator and related components. Here is what the LTC6992 circuit looked like.

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To simplify I decided to go back to my old standard NE555 circuit driving an NTD4906 N Channel MOSFET. The 555 will run directly off the 12 volt battery which eliminates the need for a regulator and for this application I do not need the precision of the LTC6992. Here is a modified schematic for the Power Straw in this iteration and a picture of the completed and installed circuit upgrade to the control box.

[View:/resized-image/__size/620x468/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-0e3b611e-6da6-4be4-8630-a1d5e0633cef/6683.contentimage_5F00_182745.bmp:620:468]

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It is easy to see the simplicity and component reduction using the NE555 as opposed to the LTC6992. Here is a wider shot of the inside of the control box so that it can be compared with the pictures in the body of the blog.

[View:/resized-image/__size/620x827/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-0e3b611e-6da6-4be4-8630-a1d5e0633cef/6014.contentimage_5F00_182747.jpg:620:827]

I will post again when the Peristaltic Pump is installed and I am ready to give the unit another test run with Mom.

RE: Power Straw

clem57 — Tue, 01 Nov 2016 12:08:40 GMT

This is very appropriate here and thanks for sharing John

RE: Power Straw

dougw — Tue, 01 Nov 2016 00:56:56 GMT

They say need is the mother of invention, mothers are also the mothers of invention.

Very nicely done John.

If you are looking for improvement ideas, you might consider using a peristaltic pump - the liquid never touches any pump parts so they are very hygienic and they are positive displacement, so you wouldn't need a solenoid or valve. (no siphoning) They should have no problem with power either - flow rate is proportional to pump speed regardless of height (pressure) - no power wasted heating up the fluid.

RE: Power Straw

shabaz — Mon, 31 Oct 2016 23:02:23 GMT

Hi John,

Great project!! It's a really clever idea.

I suppose another option to prevent spillage could be to use a hobby servo to pinch the tube (e.g. with some cam shape) and hope the cam stays there when

the hobby servo is powered off. But maybe that's not feasible or doesn't fully stop the flow.

Anyway, very cool design!!

RE: Power Straw

mcb1 — Mon, 31 Oct 2016 21:30:52 GMT

Nice work.

You can consider this one the working prototype and since it functions, it serves the purpose.

BiStable (or latching) solenoids are available, but they are pricey and designed for larger size piping and flows.

I was wondering if those battery powered water timers might be an option instead of the solenoid.

There are various types but the key part is they don't require power to stay on. (or off)

I'm sure your mother appreciates how much easier you're making her life.

Mark