Group Actions
Engagement
  • Author Author: jw0752
  • Date Created: Date Created
  • Views 3201 views
  • Likes 9 likes
  • Comments 39 comments
Related
Recommended

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:

 

image

 

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.

 

image

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.

 

image

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.

 

image

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.

 

image

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.

 

image

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.

 

    imageimage

Pictures on inside the Control Box

 

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

 

image

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.

 

image

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.

  • in reply to jw0752

    John, is it possible to feed the pump the full 12V until it's 'primed'?

    a possible setup may be to draw the MOSFET into conduction for a given short amount of time, using an RC circuit. And then handing over control to the 555's output?

     

    that would give the pump an aggressive kick of power for a brief moment, and have it moving.

     

    An RC circuit, with a Schmitt trigger, could pull the FET into saturation just for a short pulse ( a kick in the butt), and then the more moderate signal of the 555 can deliver a smooth moderate pump activity.

     

    you could put an OR gate in place (two diodes image ) to combine the two signals at the gate....

  • in reply to jc2048

    Hi Jon,

     

    Thank you for the excellent catch of this error. You and   are 100% correct. Unfortunately for producing an actual improvement in performance it is an error in my drawing of the schematic and not the actual build.  In simple circuits like this one I will usually build and then go back and produce a schematic. Unfortunately this usually happens at 2:00 AM and I am not always in my best form. I have verified that the actual circuit was built as you recommended and I have redone the schematic to accurately depict reality. The problem I am currently facing is that the thickened water sets up if it is allowed to sit too long and the little peristaltic pump has to start against a considerable load. I have experiments going on at this time where I have removed as many restrictions in the feed tube as possible and have increased the inside diameter of the feed tube overall. Originally I chose a smaller diameter feed tube so that the cord would be more flexible but that problem will probably have to be addressed by using a more silicone based hose. A hose that was soft enough to expand slightly under the pressure exerted by the pump may also allow the pump to start and come up to speed more easily. That approach will have to be tried in another set of experiments. Here is the improved schematic. Thanks again for taking the time to help me analyze this project.

     

    image

    John

  • in reply to jc2048

    I hadn't captured that the type of FET changed between the two designs.

    You may be onto something, Jon. As the voltage over the motor increases, the gate-source voltage decreases and the FET will not be driven to fully On.

    image

  • in reply to jw0752

    Maybe I'm not understanding your circuit, but it looks like you have an n-channel MOSFET controlling the pump. If the 555 output gets up to eleven and a half volts, you're only going to see eight and a half at the source, or something like that depending on what the Vgs is at the 0.3A. [You're using the FET as a source follower rather than a switch.] You might do better to put the FET on the low side of the load and use it as a switch.

     

    One other thought regarding the motor - you could, perhaps, try experimenting with overriding the PWM for the first few hundred milliseconds to get it off to a good start.

  • in reply to ntewinkel

    Hi Nico,

    Thank you for the encouragement. The Robot was a mechanical kit that my daughter and I put together 25 years ago. He was initially just mechanical and would drive a meandering zigzag path. Later I added LEDs for eyes and ran the ground through some of his joints so that the LEDs flicker.

     

    I am still fighting with the side effects and operation details of the Power Straw. Mom likes the attention and feels useful helping me debug it. Lately the nursing home has been mixing the thickened water a little more concentrated. This makes it more difficult for the peristaltic pump to start. I don't know how you guys design and make operational some of the more complicated devices. This one is really quite simple but has been giving me many challenges.

     

    John