"Saw dust bin full" Sensor
I've been toying with this idea for some time and after an 8 week period of stuffing around to get the right sensor I am finally able to make some progress.
I posted about this is earlier today in the "Developments in Dust Sensor tech" but though I would start its own thread as I guess not many folks are that interested in the technical nature of the other thread.
I got the prototype and software working on the bench last night.
Its basically a weight or force sensor that is placed under the bin to measure the weight of sawdust and to sound an alarm when a preset weight is reached.
This means it won't work on fully suspended collection bags but bins that are primarily resting on the floor or ground.
If the bag is resting on the base of the DC frame a hinged secondary base could be added and this sensor could be placed under the side opposite the hinge.
The force sensor is that gold foil rectangle which is an up to 50kg rated thin film variable resistor.
The resistance ranges from >500kΩ near zero to around 70kΩ at 50 kg.
Placed in a voltage divider the output V can easily vary enough to be picked up by a microcontroller.
https://www.woodworkforums.com/attach...2&d=1501723435
The resistance of the force sensor is inverse exponential and I calibrated it on a set of bathroom scales using lead weights.
The force sensor will be embedded into a thin rubber pad and placed under the front bottom edge of wheelie bin collector at the mens shed.
The wheelie bin wheels should take about half the weight and the front edge of the bin should take the other half.
The sensor will be connected to the micro controller/display back inside the shed where the % fill of the bin is displayed on an LED display.
Switch "Sw" can be switched to display the required alarm level using pot "P" .
Then Sw is set back to display.
When %fill of bin exceeds the alarm level the alarm (A) will sound.
Of course a bigger alarm on a relay will be used in practice.
https://www.woodworkforums.com/attach...3&d=1501723460
A secondary calibration will be needed with the sensor under the bin font edge and will take place with the bin near full
Trim pot "T" is part of the voltage divider and is part of the secondary calibration system.
The microcontroller is a $4 Arduino Uno clone.
The LED display costs $4
The Sensor costs $11
Total cost of parts is ~$25, excluding the alarm - given how deaf the men's shed members are it will need to be LOUD.
As usual the much of the real work is in the turning the prototype into a robust actual product.
Sorry am not making these for sale but the details and micro controller software will be freely available to anyone that wants it.
Now I have to assemble it into an actual unit.