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Re: Active alternating air cushions???

PostPosted: 05 Sep 2018, 09:58
by Burgerman
I or we are confusing units. mpa baffles me! Your sensor may be good. Although why you need to run an arduino for a pump timer confuses me. And adds complication.

The pump run at pressures like the spec of my professional bought pump. It reads:
Pressure: 70~90 mmHg. And can be set lower. 60 seems about right in use for me.

And being british we use P.S.I. for pressures usually. So thats approx 1.75psi max.

Re: Active alternating air cushions???

PostPosted: 06 Sep 2018, 08:58
by snaker
For those prefer programmable boards, I found a very good pressure sensor. ... 0b5311e301

But the price is fairly high, about $10 for each. Shirley, is there any cheaper alternative? I just need sensors that are relatively accurate and ... cheap :mrgreen:


Re: Active alternating air cushions???

PostPosted: 08 Sep 2018, 08:39
by snaker
BM, can you post the link where you bought your solenoid valves?

Re: Active alternating air cushions???

PostPosted: 08 Sep 2018, 08:58
by Burgerman

Re: Active alternating air cushions???

PostPosted: 08 Sep 2018, 09:50
by snaker
Do its specs mean that 100cc 300mmHg tank can be empty through the opened valve in less than 3s? If so, is this speed too fast? In case an air cushion, if the valve is opened, the cushion will be empty in a very short time (e.g 15s). And a pressure cycle high-low-high will complete too fast. That is not a good alternating, isnt it?

Air speed: <3s (100cc tank from 300mmHg to 15mmHg)


Re: Active alternating air cushions???

PostPosted: 08 Sep 2018, 10:29
by Burgerman
It only releases the air, after the opposite cells are at full pressure. Triggered by the opposing cells pressure switch. In my case I will have the switches do 2 things.
Turn off pump1, and release air from pump 2. And...
Turn off pump2 and release pressure from pump1.

So they are cross linked. Meaning at any given time one group of cells is always at full pressure. Theres never a time where one is deflating while the other is inflating.

So it doesent matter how fast it empties. But you can easily slow it by fitting a short tube to the other end of the solenoid. With a restrictor, like a small control oriface. Say a small brass control jet if you need to slow it down. Or in your case with arduino you can send it a 50% pulse, or 25% pulse, at 5 hz. To make it half or a quarter the flow.

Re: Active alternating air cushions???

PostPosted: 08 Sep 2018, 10:56
by Burgerman
Meaning no arduino required. Just 2 simple timers. Linked to remain in sequence like this. ... 2749.l2648

In fact you really only need 1 timer, with single normlly open, and normally closed output. But the above allows say 10 seconds overlap time. And or easy switching to have all inflated while you transfer.

It can use an analog pressure switch (has adjustable trigger voltage) or not your choice.

Read the chinglish:

EAZY-VLC 2.0 controller can be achieved by adjusting the timing of the joint action approach dual relay, two time relay can be independently timed pull respectively, can also be individually timed turns to pull, and can control the time of the relay by detecting dual voltage.
By using this product, you can control two loads simultaneously or alternately on and off, such as: single-phase motor control timer reversing all the way, or the way the timing Reversible DC motor, or two-way solenoid valve timing control work in rotation(controlled pneumatic), or two-way indicator turns off and so on. Multiple boards can be cascaded to achiece multi-channel timer turns off cycle.


Four digital tube display, three keys for easy operation, restore factory settings function.
High performance control chip for high stability and low power consumption.
The tube display can be automatically shut down, has power supply reverse connecting protection.
Dual time relay, adjustable timing range: 0.1-9999 minutes, can be single time or cycle and release; adjustable cycle number 0-999(zero for the infinite loop).
Each relay contacts for common point and normally open, normally closed point, a total of two sets of transformation.
Dual time relay can joint action in turn; multiple boards can be cascaded to achieve multi-channel timer turns off cycle.
Dual time relay can run independently at the same time, can use high level or switch trigger start mode(P-4).
Dual voltage detection control dual time relay, detecting voltage range: DC 0-99.9V.
All setting parameters can be stored after power off, and operates the last mode and parameters when power on.

Modes Selection:
P-1: A channel time (time) relay
P-2: B channel time (time) relay
P-3: A, B two way joint time relay (A first and then B, can recycle)
P-4: A, B two way independent time relay (A, B independent cycle time at the same time)
P-5: A, B dual voltage control time relay
P-6: Digital tube automatically turn off time and reset

Relay Voltage: DC 12V
Working Power: DC 10-16V
Voltage Detection Range: DC 0-99.9V
Error: (+/-)0.1V
Timing Range: 0.1-9999 minutes Adjustable
Cycle: 0-999 times Adjustable
Two way, each of a set of transformations(normally open/normally closed)
Contract Load: 10A/277V AC, 10A/30V DC
Contract Resistance: ≤100mΩ(1A-6V DC)
Mechanical Durability: >10 million times
Electrical Durability: >100,000 times (10A-250V AC)
Working Current: 18mA 12V, Min. Standby Current: 7mA/12V
Working Temperature: -40-85°C
Dimension: 107 * 48 * 17mm / 4.21 * 1.89 * 0.67in
Weight: 55g / 1.95oz

Re: Active alternating air cushions???

PostPosted: 11 Sep 2018, 04:09
by ex-Gooserider
Not sure if they would be the right pressure range or not, (I suspect they might be to low pressure) but it might be worth looking at the pressure switches they use in clothes washing machines to tell when the tub is full... They stick them up near the top of the tub with a hose to the bottom, so that they open and close as the pressure changes...

Some models are adjustable...

I used it as a check device on a pool pump controller - if the pump was actually producing pressure it was OK, but if the pump wasn't running, or if it wasn't making pressure because the skimmer was clogged or the water level was low, it triggered a shutdown....


Re: Active alternating air cushions???

PostPosted: 07 Oct 2018, 05:49
by ex-Gooserider
Bringing this back up to add a possible info source... A week or so ago the Open Source Hardware Association had their annual conference here in Boston, and among the other presentations was a guy showing off his work on "soft robotics" which is the concept of using low pressure air to power various sorts of robotic gear, some practical some more artistic... He had created a microcontroller based addon board system called " Programmable Air".... It works in the sort of pressure range needed for a cushion. I had a quick discussion with the guy and he said it wasn't something he had tried, but that he thought it would be a possible application.

Main site:

Hack a Day online articles about it ... mable-air/

Github source page

I thought it was interesting both in and of itself, but also because he has some good discussion of the general problem and some of the stuff (including parts references) that he both experimented with and ended up using...


Re: Active alternating air cushions???

PostPosted: 07 Oct 2018, 14:30
by Burgerman
Ebay ... SwhT1bHjYl

Cushion has 4 zones. And a cover. Is £108 UK pounds.
-Inflate green, and blue outer edges/front to 2psi, firm, and permanently.
-ALTERNATE the central rear yellow and pink areas with your pump every 5 mins.

Re: Active alternating air cushions???

PostPosted: 15 May 2019, 20:11
by tutatu
Does this type of cushion's material allow inflating while sitting on it?

I'm asking because for example, Roho's recommendation is to overinflate and when you sit on it, then release air from cushion to accommodate your needs.

I was lying on an alternating air mattress in hospital for two months and was a lifesaver because not all nurses know how properly turn quadriplegic. To avoid potential skin shear and pulling and various nurses turning skills, with alternating mattress I could be lying longer periods of time on either side with zero redness on the skin.

What I didn't like about alternating mattress is when you finally find a comfortable angle to fall in sleep, chambers take inflate/deflate cycle and my body totally change lying position + sheats are slippery on that kind of plastic rubber material.

And yes, the buzzing of compressor/pump drives me insane, especially in the night when everything is quiet.

Driven by logic, if the mattress is good then why can't be a cushion.

After flap surgery on left coccycyxcyx in 2016, I still have a great danger to destroy skin if I would sit 10 days for 12 hours. Now I'm sitting 6 hours max.

I have high Roho but tied down 4 cells to avoid direct pressure. The hole is filled with 5-6 cm of memory foam to prevent negative pressure to that area. For now, it works.

I'm very interested in your project. :ugeek:

Re: Active alternating air cushions???

PostPosted: 15 May 2019, 20:21
by tutatu
Now I see. Neoprene like Roho.

Just nowhere to find is it alternate possible?

Re: Active alternating air cushions???

PostPosted: 15 May 2019, 22:27
by flagman1776
I can find the bumpy inflating cushion but can't find the automatic air pump / controls. I could see hanging the pump & controls off the side of the chair, below seat level.

Re: Active alternating air cushions???

PostPosted: 10 Jul 2019, 07:27
by iainsherriff
Now you have perfected the cyclic cushion principal, how much would it take for someone to turn it into a realtime reactive system reading individual cell/tube pressures and so cycling on that basis rather than a timing basis, or is that over egging the whole thing ?

Re: Active alternating air cushions???

PostPosted: 10 Jul 2019, 10:59
by Burgerman
Very much. Its not about pressure at all. As long as its high enough to support your weight. Its about MOVEMENT. Its about supporting your weight on different points. Allowing the other areas, to have no weight half of the time. So that blood can circulate to those parts every few minutes providing oxygen and keeping the skin healthy.

You need enough pressure. But thats very low.
You need the supporting cells to be split into 2 groups. And these alternate allowing blood to get to the deflated half. Every few mins.
Pressure not at all critical.

What is critical is the time period. The more frequently they swap over, the better for your backside. Anything from 1 to 15 mins seems to work fine. Faster means more battery drain. Slower means more time on the high pressure bits, so more likely to cause sores. Its a balance. But my pump, has 24 hour capability so at 10 min interval, it can go for longer than I can stay awake.

Re: Active alternating air cushions???

PostPosted: 10 Jul 2019, 11:02
by Burgerman
This is a portable digital, quiet, pump. Its not cheap. It is reliable, lithium powered, and quite small. It allows varied timer, and adjustable pressure, and runs for a day. ... shion.html

Alternatively, buy this complete, throw away the hopeless foam part and make your own as I did in the right size from hard conglomerate foam made from glued particle or fragmented foam sheet. ... shion.html

Re: Active alternating air cushions???

PostPosted: 13 Jul 2019, 22:33
by sacharlie
Burgerman wrote:
No, it's all one size grids & you are right about air circulation. Unless you place it on a vented base, there can't possibly be air circulation. Maybe if someone built a base with air channels & a blower??? WHEE!!

The alternating air cells on the cushion I ordered have tiny holes that blow air when inflated. Thats how they deflate.
This applies to 3 mattresses and to the 240v powered cushion, and to the newer mobile cushion I ordered.

Key features

Nylon TPU coated cells
Independently removable cells
Micro-perforated cells
Multi-stretch PU cover
Water resistant, vapour permeable cover
Antimicrobial, machine washable cover
Robust pump connection
Transport mode

1 vid covers beds and cusions. ... 502-ALT215

BM this is the low air loss I ask about in another thread. As this cushion and others state low air loss micro holes. It seems the pump ends up running 100% of the time whether in static mode oe alternating mode ,no?

Re: Active alternating air cushions???

PostPosted: 13 Jul 2019, 23:50
by Burgerman
No. It stays inflated overnight while OFF. No microholes in the portable cusion. There are holes in the mains powered matresses.

Re: Active alternating air cushions???

PostPosted: 05 Aug 2019, 14:15
by AlexAGF
I also can’t cure bedsores for 6 years. The situation is only getting worse with every wheelchair ride.
ROHO and Supacor are shit.
BM, did you kind of buy Alerta Mobile Air Flow Seat Cushion - High Risk? What did you think of it?
Can you advise any alternative?

Re: Active alternating air cushions???

PostPosted: 05 Aug 2019, 15:19
by Burgerman
Yes. It works. Nothing else did. Way overpriced. I made my own cushion base as the one they supply is a joke. Read all thread.

Re: Active alternating air cushions???

PostPosted: 05 Aug 2019, 15:59
by AlexAGF
I am interested in cushions for patients with a very high risk of pressure sores.
Should I pay attention to the following?
1. ... shion.html
2. ... nsity.html
3. ... shion.html

It is interesting why cushions with a compressor are simply declared "high risk", unlike those listed above.
I'm afraid that I will not be able to make a solid foam cushion mold.
The following cushions are only suitable after remodeling?
1. ... shion.html
2. ... shion.html
3. ... ystem.html

Why is there such a big difference in price here and here?

Re: Active alternating air cushions???

PostPosted: 05 Aug 2019, 19:07
by Burgerman
First 3 are all a waste of time. Been there, got the T shirt, they dont work. Movement is the thing that does. At least for me.

Those last 3 cushions are all the SAME cushions. With small variations. Some are lithium 24 hours, some are 12 hours, some are nicad cells. It MAY be that some use different pump internals, not sure. They all look the same.

Price differences? Different amounts of profit...

And the cushion bases are to me, all unusable floppy junk that offers no support and are too small. But they do appear to cure the problem.

Re: Active alternating air cushions???

PostPosted: 09 Aug 2019, 14:24
by AlexAGF
What specific types of foam did you order?
I cannot understand from the description what I need ...

Re: Active alternating air cushions???

PostPosted: 09 Aug 2019, 14:48
by Burgerman
Very Firm - (6lb Recon)
A very high density foam. Used where maximum support is required. Often used as a base to which a softer foam is bonded to. Suitable for high usage applications, bar seating etc.

Re: Active alternating air cushions???

PostPosted: 09 Aug 2019, 15:10
by AlexAGF
Very Firm - (6lb Recon) - This is the basis.
And 2 and 3 layer what?

Re: Active alternating air cushions???

PostPosted: 09 Aug 2019, 15:26
by Burgerman
Nothing really.

Thats what you make the full cushion with. I added an extra 8mm on top, of the blue medium foam.

So 1 inch of the firm stuff full sheet on the bottom.
1 layer of fabric on top of that (almost any like say cotton or something non stretchy to stop the cushion "growing" in width and length when sitting on it for a few weeks. And the top 2 inches in that same firm foam. (With a thin 6 to 8mm of soft /medium stuff on top. Not essential). You need the correct glue - the foam supplier will sell this to you. Or get them to assemble it for you. Do a drawing for them.


To suit YOU. But use the correct foam glue.

Re: Active alternating air cushions???

PostPosted: 09 Aug 2019, 15:31
by Burgerman

Get cut like this

Fix togetherLike this.. Blue is 6 to 8mm medium. The widest bit (front left nearet camera, is the front, under legs)

3 bits of foam.

Base 1 inch, hard foam.
Middle 2 inch hard foam, with cut out.
top, blue medium foam thinnest layer you can easily buy.

Re: Active alternating air cushions???

PostPosted: 09 Aug 2019, 15:53
by AlexAGF
BM, Thank you!

Re: Active alternating air cushions???

PostPosted: 22 Aug 2019, 15:13
by flagman1776
The small but painful area on my bottom was nearly gone after alternating between the blue honeycomb cushion and the Apex alternating air cushion. With the desk chair I'm using at the computer, it takes more effort to keep my position with the Apex than the honeycomb. But the sore spot came back.
I switched to the Apex all of yesterday... pretty much pain free all day. I'll have to put up with the fatigue... I am back on the air cushion.

Re: Active alternating air cushions???

PostPosted: 22 Aug 2019, 15:38
by Burgerman
They do seem to be very good. No matter cheaply made and overpriced.

Personally I am trying to buy a ... heelchairs
That seems like it will prevent ALL pressure on the Ischael tuberosities and cocyx (cant spell that) completely. And put your weight only on the bits that are not sensitive to pressure.

But cannot find any way to get hold of one in the UK. Any ideas? eMAILED THe company. No reply.