- the readings are all very high; I think it needs a resistor, maybe.
- nope, this was wrong, it just needed a pull-down resistor, not the resistor I was thinking of
- now the readings are really nice
- I think the proper wiring is +3V to FSR_1 though FSR out FSR_2 to MCP3008
pin 1, and this is where I think the resistor should go to ease up on the
range. Or something. (This is in addition to the wriring instructions at
learn.adafruit
- this was also wrong
- the correct thing is that it needed a pull-down resistor, as mentioned at https://learn.adafruit.com/force-sensitive-resistor-fsr/using-an-fsr
The mechanics of FSRs are tricky. There are some web pages I had seen about this. It is hard to get constant firm pressure on them.
One approach that seems to work is:
coffee |
container |
|
-------------+
+--------+
| penny |
+--------+
+-------+
| fsr +-------------- to breadboard
+-------+
A photo of this set up is here:
With that set up, 12oz of coffee changes the reading by between about 60 and 100, which is a pretty narrow range. With some better balance, it changes by about 200.
I think this has become a mechanical engineering problem.
I’m also thinking of something like this:
+------------------------------+
| |
| |
| Coffee Can or Bag |
| |
| |
+-+ | |
|G| | |
|u| | |
|i| | |
|d| | |
|e| |{s} |
| | +------------------------------+
+-+--------------------------------------+
| Platform |
+--------------------------------+-----+-+
/\ | |
/ \ +-----+
+-------+ to breadboard
| FSR +-----------------
+-------+
or, represented in SketchUp:
