[Lab] Question(s) for the Collective: Pressure sensors

Wed Apr 11 10:08:18 EDT 2012

On Wed, Apr 11, 2012 at 08:57:14AM -0400, Henri Kuschkowitz wrote:
> Hey Raj,
> 
> That is an idea I had read a while back. I do find this solution
> simpler though I would have to cut the plywood into smaller pieces to
> account for the space since I need to capture multiple people walking
> around  (on the plywood) at the same time. 

Instead of springs, you could use a layer of foam with a grid of
microswitches, wired however you like, to as many inputs as you like.

> I think I will test this idea out especially since microswitches are
> dirt cheap. Will keep you posted.

And they're in all sorts of discarded appliances...

> Thanks a lot guys!
> Henri
> 
> On 2012-04-10, at 2:41 PM, Raj wrote:
> 
> > both fluidform and pressure sensors seem like they'd be overkill for a simple on/off requirement.  How about 2 sheets of plywood hinged at one end with a microswitch at the other end?  You may need to add a spring to keep the top sheet lifted when there's no weight on it and you can size the spring to have sufficient stiffness so that there's a minimum weight that will trigger the switch.  Total travel only needs to be a few mm so should not be noticable to someone stepping on the pad.  
> > 
> > You will need to put a hard-stop on the movement, I doubt microswitches alone can take the weight of a person.  And if there's issues with distortion, eg one corner coming down before the other due to uneven weight distribution, perhaps a couple more microswitches under the end edge would do the trick - wire them all in parallel and any switch on would indicate a step on.
> > 
> > cheers!
> > --Raj.
> > 
> > 
> > 
> > On Tue, Apr 10, 2012 at 1:59 PM, Henri Kuschkowitz <henri.kuschkowitz at gmail.com> wrote:
> > Great stuff! if not for this project i will definitely look into them for other ones. 
> > 
> > 
> > Thanks a lot!
> > Henri
> > 
> > On 2012-04-10, at 1:49 PM, Tom Burns wrote:
> > 
> >> Hi Henri
> >> 
> >> An AVR chip is what powers an arduino.  If you developed the solution with an arduino you could then use your own minimal clones for the rest of the microcontrollers and save some money.
> >> 
> >> Hardware-wise, an Arduino is basically an AVR microcontroller pre-flashed with a bootloader that supports serial uploading of code, with the supporting circuitry necessary to run & support serial USB.
> >> 
> >> I've used AVRs since before the Arduino was popular.  There's a bit of a headache in programming them compared to an arduino as off the shelf you can't just plug them in over USB, but once it had the arduino bootloader installed it'd be almost as simple as the arduinos for programming.
> >> 
> >> Tom
> >> 
> >> On Tue, Apr 10, 2012 at 1:45 PM, Henri Kuschkowitz <henri.kuschkowitz at gmail.com> wrote:
> >> Wow,
> >> 
> >> Thanks Tom. that was quite a quick response. The reason for using Arduinos is that I already have one (possibly two) available. I have heard of AVR chips before, but never used them nor do I know much about them at this point. I will definitely review them. Have you used them before?
> >> 
> >> 
> >> Cheers,
> >> Henri 
> >> 
> >> On 2012-04-10, at 1:40 PM, Tom Burns wrote:
> >> 
> >>> Hi Henri
> >>> 
> >>> If low cost is a goal I strongly suggest AVR chips with supporting circuitry instead of complete arduinos.  The chips + supporting circuitry come in at under $10.  If you find someone with an AVR ISP programmer they can load the arduino bootloader to the chips so further software revisions can be uploaded via serial.  Should bring the per-microcontroller cost down to ~$10.
> >>> 
> >>> Tom
> >>> 
> >>> On Tue, Apr 10, 2012 at 1:37 PM, Henri Kuschkowitz <henri.kuschkowitz at gmail.com> wrote:
> >>> Hi everyone,
> >>> 
> >>> I am hoping to be able to access the collective mind to get some information regarding pressure sensitive sensors for a possible project  for the upcoming Nuit Blanche here in Ottawa.
> >>> 
> >>> I would like to gather the input from people walking over a defined area on the ground (8"x10" possibly larger). Technically, only a digital output (step on/off an area) and no analog data would be required. Since there is no compensation for this project a low cost for material is a big factor in my research.
> >>> 
> >>> After a short analysis, I came to the conclusion that the cheapest alternative to buying any kind of sensors would be creating them by myself, similar to fluidforms or a pressure sensor matrix, and to combine them through multiplexing using one (or more) arduino(s). The sensors would be either mounted between sheets of plywood, possibly fabric or similar. The installation would be outside, so I have to factor this in for what material to use as well. 
> >>> 
> >>> My question would be whether any of you have any knowledge or advice regarding such an endeavour, whether or not I might be on the right track or should look into a different (possibly simpler) alternative? Also, I am not completely certain whether there would be any issue with multiplexing when a couple of sensors are capturing an input at the same time?
> >>> 
> >>> 
> >>> As always, I more than appreciate any good advice!
> >>> 
> >>> Thanks in advance,
> >>> Henri
> >>> 
> >>> 
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