The issues that we've had with the environment over the past week or two have underlined the need to protect all of our designs from anything that the world can throw at us
We are still having problems with water ingress into the Resistance Probe electronics; even with the new plastic 'caps' for the Pi Board and Wireless Access Point, but that's a problem that is relatively easily overcome when we develop the 'production' models.
Of more concern has been the erosion / corrosion of the wet contacts of the Resistance Probe, which means that for this type of sensor to be reliable, we'll have to identify probe materials that are stable in such a environment. Maybe this isn't such a good approach.
I mentioned our problems to the guys at the Linux User Group Meeting on Tuesday evening and Paul (who Penri and I used to work with), suggested an alternative approach; a magnetic sensor. The attached diagram should illustrate the technique. The beauty of this design is that anything carrying electricity is sealed from the water inside a tube. The collar that has been drawn at the bottom of the tube will slide up and down it as the water level rises and falls. When the collar is adjacent to a reed relay, then it will be energised and an active high signal will be routed to the Pi. (Active low designs are also possible if required and may be better.)
Those are the advantages, but there are some disadvantages of such a system:
- Mechanical problems:
- Debris in the water could get between the collar and the tube, jamming it in one place.
- If the sensor is placed inside a bigger tube (such as we might want to do at the butts), the sensor will have to be very narrow or the outer tube very wide to avoid debris in the water getting between the collar and the outer tube, jamming it in one place.
- Electrical / Electronic problems:
- How do we know where the collar is if it is floating between relays?:
- Lots of relays, so that one is always energised. That becomes a problem in itself because we would then need a lot of GPIO pins and buffers.
- Keep track of what relay last triggered and assume that the level is in that 'zone'.
- There may be more problems that I haven't thought of.
- How do we know where the collar is if it is floating between relays?: