Once again I have been tripped up by my inexperience using a multimeter but at least I'm learning a heap load and in real hands-on style!
Let me explain...
In my last post, I indicate that I had decided to go with the Plusea pressure sensor for a myriad of reasons but most notably because of my perceived stability of the test measurements taken and the flexibility of being able to easily manufacture any shape and size of sensor I desired.
While I still believe that the Plusea sensor is a very stable and more linear sensor, after I hooked it up to my Arduino using a simple voltage splitter scheme ( ... I'll go into this further in my next post), it became apparent that something was up.
My assumption was that the Plusea sensor, when not under pressure, would act just like a switch switched off or a potentiometer turned all the way off, providing infinite resistance and preventing all current flow.
But, the readings from the analog port on my Arduino (and pumped to the console window of the Arduino IDE) indicated a value near the maximum reading (1023) at all times... even when not pressed!
At first I questioned my circuit design, but after a thorough tracing of the entire configuration I decided to sanity check the sensor by passing a current through it and reading the voltage and current using my multimeter.
Long story short, what I realize now is that the Plusea sensor was always allowing some degree of current through, even when not under pressure.
Switching my multimeter back to resistance, I finally noticed that, when set to a range of k-ohms, the Plusea sensor was always reading some non-infinite level of resistance.
After realizing this I became a bit stubborn and decided to see if I could manage this resistance "leakage" by swapping out the other resistor in the voltage splitter circuit to sort of counteract the leakage and I was marginally successful at bringing the default, non-pressured Arduino reading down to 300 but this still seemed unworkable.
Then, hooking the "Boston" sensor up to the same voltage splitter circuit, it was obvious that this sensor was more suitable to my application with a reading near 0 by default ( ... i.e. no pressure applied) and what appeared to be some nice range up to the heavier weights.
Looking back at my comparison matrix, I suppose I should have been able to predicted this outcome:
Notice that for the Plusea sensor, the average range of resistance was 604 ohms for the minimum weight to 144 ohms for the heaviest weight.
As it turns out this was an indication that there wasn't enough range of resistance with the minimum resistance just over 4x the maximum while the Boston sensor's rage was more like 31x.
Further, remember that I noted that the Plusea sensor was able to resolve a consistent resistance reading of a SIM card ( ... in the range of 30 k-ohms) which I delighted in at first, but looking back, that was another indication that the range was not suitable for my application.
Note that the Boston sensor required the weight of a AA battery just to register in the range of 30 mega-ohms.
I now interpret all of this to mean that the Plusea sensor was VERY sensitive to the touch with the resistance falling all the way down to 30 k-ohms with a weight of just the SIM card and registering some degree of conductance at all times (i.e. even without the presence of any pressure) while the Boston sensor provided infinite resistance when not under pressure and required 178 lbs just to get resistance down to 33 k-ohms.
Another way of looking at this is that the Boston sensor required 178lbs to get the resistance down to the same level that the Plusea sensor registered with just the weight of a SIM card.... a BIG difference indeed!
So, I'm now back fully engaged with the Boston pressure sensor again and, having learned quite a bit in process of comparing the two, feel more sure now that I'm on the right track as far as the pressure sensor is concerned.
In my next post, I will feature my split circuit Arduino configuration and summarize a sample of output data across a range of weight.
Best to all...
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