Water level sensor

[megatron]

Thankfully Eddy my definition of fast does NOT include Fiats.
Stew

[Eddy Matthews]

Thankfully Eddy my definition of fast does NOT include Fiats.
Stew

We certainly agree on that one Stew! 

Eddy

[megatron]

TAG
I've just read your article in ME which I found very interesting.
I am disappointed to hear that the Optek sensors gave variable results. I found exactly the same thing using home made sensors and was thinking about using the Optek ones to get over this problem.
You say you had to use a variable resistor on the pcb to calibrate these. You could calibrate the sensor on a test rig and instead of using a variable resistor on the pcb use a small 1/8w resistor in the lead to the sensor, all the sensors would then read the same, independant of the pcb, making it possible to replace the sensor without any further adjustments.

Ray
Have you got your system up and running yet?
Stew

[TAG]

megatron
Pleased you enjoyed my article in ME.
I agree your system of calibration would be the way to get over the problem. I think it would be better to feed the output of the Optek sensor into an op amp in max gain mode such that the change from water to no water would cause a swing from 0v to +5v then the PIC would know exactly what to do!
You probably gathered from my article that I have abandoned my work on the optical system because of the bubble problem and am standardising on the electrode system. I have some prototype optical set ups that I could let you have to play with,pm me to discuss.
Regards
Tim

[megatron]

Tim
Even if you use an opamp to supply the pic you still run into the same problem.
I use opamps in my system with the reference voltage set at half supply voltage (2.5v) and using various values for the resistors to the led and the phototransistor the best I could achieve was a swing of from 2 to 3v for high and low water. These values could easily change by over 0.5v from one sensor to another.
I would love to know what components Cheddar used in their sensors. I have had a look at one and there appears to be an ir led and some form of detector which has 4 conductors coming from it. This detector is wrapped in aluminium tape with a very fine slot cut in it, the tape also covers any indentification numbers which may be on it.
I'll email you to discuss trying one of your sensors.
Stew