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  • Author Author: jw0752
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Power Straw

jw0752

For several years my Mom has been in a Nursing Home with Parkinson's disease. As she has lost function of her muscles I have attempted to use technology to assist her. I have posted a couple of my attempts to assist her in my Blog on E-14.

 

https://www.element14.com/community/people/jw0752/blog/2015/07/07/hacking-a-lift-chair

 

https://www.element14.com/community/people/jw0752/blog/2016/01/15/building-an-led-amplifier-for-mom

 

Recently on her bad days she has been too weak to draw the thickened water she has to drink up a straw. This causes her to become dehydrated and quickly affects her health. She is very stubborn and will not allow herself to be fed by other than by herself. To help her in the days that she is too weak to drink through a straw  I have constructed this little device to assist her. I call it a Power Straw. It is very light on electronics so perhaps it does not have much application to our electronics site but since I had published previous projects I though a few of the guys would be interested.

 

Here is a schematic of the project:

 

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I began the project by collecting a variety of potential components. My Goal was to draw her thickened water from a reservoir and pump it up a line and into her mouth. She is accustomed to using a push button call switch when she needs help from an attendant so I decided to use a very similar switch to actuate the pump.

 

The water line would run axially with the switch and its wiring. The switch could be held in her hand and the water feed line would continue past the switch by about 4 inches.

 

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Picture of Hand Switch

 

I decided to try a small 12 volt water pump, that is usually used in small fountains, to pump the water from the reservoir.

 

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Picture of Pump in the Reservoir

 

My first prototype did not include an in line solenoid. This created a problem if the cord accidentally fell to the floor as gravity would siphon the water from the reservoir and create a big mess on the floor. My final prototype needed a solenoid.

 

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Solenoid Picture

 

Since space and weight were not a particular problem I decided to use two 6 volt 4.5 Ahr Lead Acid Gel Cells for the batteries.

 

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Battery Picture

 

A small Volt Meter circuit was incorporated in the control box so I could check the level of the battery and recharge it when needed.

 

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Control Box Picture

 

The control box is very simple with the Volt Meter and a momentary switch to activate it, a single P Channel MOSFET, Jacks for: Batteries, Charger, Pump, Solenoid, and actuation switch.

 

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Pictures on inside the Control Box

 

The Reservoir is an lightly insulated hospital drinking cup that I brought home after a past overnight adventure.

 

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Picture of the Reservoir.

 

Here is a picture of the finished project before I took it to Mom's room and nylon strapped it to the back of her wheel chair.

 

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Picture of completed assembly

 

I can see room for many improvements. The parts that I ordered and received did not meet my imagined specifications. For example the pump could have a little more power and the solenoid draws too much current. While the batteries will be heavy enough to deal with the present solenoid, ideally, I should be able to find one that uses 200 mA or less instead of the current 400+ mA. I have made the reservoir and hand cord easy to disassemble for cleaning but improvements can be made. The plugs that were used on the pump and the solenoid were not polarized. While this will not affect the solenoid it is important the the pump spin in the correct direction for maximum efficiency. I have marked the non-polarized plugs but someone other than me might miss this detail. For the time being however Mom is happy and after the newness wears off she too will have some good suggestions for her sonny boy on how he can make it better.

  • Hi   & ,

     

    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:

     

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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       I was surprised to find another idea for this modification from     . 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.

     

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    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

  • in reply to jw0752

    A P-channel FET between the positive rail and the gate of Q2 could work.

    The gate of this FET would have a 1M pull-up to the rail and a 1uf cap to ground.

    The gate of Q1 will be high until the capacitor charges up, then the new FET is dormant.

  • in reply to jw0752

    Hi John,

     

    The method Jan suggests is fairly essential to get it to operate at low speeds. There is also a general way of doing it, but it is awkward. The problem with PWM on its own is (as can be seen) the lack of torque at low speeds. If the peristaltic pump is hackable then the motor could be replaced with a stepper motor but then a controller for that is needed/ Another way is to get some feedback off the motor shaft (before it is geared down) so you can feed it into a servo controller type circuit where the pulses off the shaft will be compared with a set value from your potentiometer. This could be achieved maybe by using bits from hobby servo motors, but again will be difficult. If you do see a way of getting pulses from the shaft (e.g. attaching a magnet) then something like MC33030 or MC33033 (it is actually intended for brushless operation but it can be used in a brushed motor mode) would work, but the trouble is they are obsolete. I do have a board I made with a MC33033 on it, and the board could be repurposed for your project. Let me know if you want to pursue that method, and I'll get it sent across. It will require fiddling with R and C values to get the pulses from the shaft sensor to a suitable form for comparing with the potentiometer setting, etc.

    Alternatively a microcontroller could be used, to detect when the shaft is not rotating (from the magnet and a digital output hall sensor) and increase the pulse width to get it moving again. That might be the easiest to be honest. If you want to go that route, I'd suggest a FRDM-KL25Z board and I can help you with the software. This method would just require the shaft magnet/sensor, and a FET for your motor which you already have in the circuit anyway, provided it can be switched from 3.3V which is what the FRDM-KL25Z output will be. The PWM can be implemented in software in the KL25Z board, and it has an analog input for the adjustment potentiometer too. Basically with all these methods, the closed-loop feedback from the sensor will always ensure that the motor is never stalled even at slow speeds.

  • in reply to jw0752

    Say Hi to Mom, and good luck with the experiment.

  • in reply to Jan Cumps

    Hi Jan,

    I really like your idea to start the pump with a 1 or 2 second full power boost. From your good description you have done all the hard work for me already. Tonight I will start the fun part and try to breadboard the circuit that you described.

    John

     

    I will tell Mom today about all the help I am getting designing her drinking machine from engineers all over the world. She will get a kick out of that.