I've been using Velleman K2639 Liquid Level Control kits for Hi/Lo level water pumps controllers: http://www.vellemanusa.com/us/enu/product/view/?id=350507
I've used these in roof drain sumps for "Green Roof" vs "Non-Green Roof" rain-runoff measurements, and they worked very well.
I was going to use one for an automated Christmas tree stand watering system. This was to replace my old, unreliable, float-switch (home brew) system. I've been thinking that this could be a good PICAXE 08M project. I used their concept of AC driven level sensor electrodes, that I've also seen in other designs. The common electrode was driven by an oscillator, through a DC blocking capacitor. The two sense electrodes detect the AC signal through the water and drive capacitor-coupled voltage-doublers to opamps and logic.
For the PICAXE design I drove the common electrode with a 50/50 50KHz PWM output through a capacitor and resistor. The sense electrodes, through two voltage-doublers, drive two ADC inputs. The output drives the LED in an SSR, to control a 120VAC pump.
I have not assembled it, except for the sensor probe, but the bench test gave me very satisfactory results. The output of the voltage-doublers was ~0.4vdc to ~3vdc, depending on depth of the electrode in contact with tap water.
Ken
I've used these in roof drain sumps for "Green Roof" vs "Non-Green Roof" rain-runoff measurements, and they worked very well.
I was going to use one for an automated Christmas tree stand watering system. This was to replace my old, unreliable, float-switch (home brew) system. I've been thinking that this could be a good PICAXE 08M project. I used their concept of AC driven level sensor electrodes, that I've also seen in other designs. The common electrode was driven by an oscillator, through a DC blocking capacitor. The two sense electrodes detect the AC signal through the water and drive capacitor-coupled voltage-doublers to opamps and logic.
For the PICAXE design I drove the common electrode with a 50/50 50KHz PWM output through a capacitor and resistor. The sense electrodes, through two voltage-doublers, drive two ADC inputs. The output drives the LED in an SSR, to control a 120VAC pump.
I have not assembled it, except for the sensor probe, but the bench test gave me very satisfactory results. The output of the voltage-doublers was ~0.4vdc to ~3vdc, depending on depth of the electrode in contact with tap water.
Code:
'Picaxe 08M two-level-water-control-09.bas
'Ken Moffett 4/20/2009
'Pump starts when water is below lower sensor
'Pump will run until water is above the upper sensor.
'Pump will remain off until water is below lower sensor
'output 0 (leg 7) is pump driver
'input 1 (leg 6) is low level sense
'output 2 (leg 5) is sensor driver
'input 4 (leg 3) is high level sense
pwmout 2,19,40 'PWM output 50KHz@50%
low 0 'turn pump off
main:
b2=0 '0=empty, 1=not empty
b3=0 '0=not filled, 1=filled
readadc 1,b0 'read voltage at lower level probe
if b0 > 25 then gosub notempty '<26 is empty
readadc 4,b1 'read voltage at upper level probe
if b1 > 25 then gosub full '>25 is full
if b2=0 and b3=0 then goto pumpon 'empty
if b3=1 then goto pumpoff 'full
goto main
notempty:
b2=b2+1 'increment level
return
full:
b3=1 'indicate full
return
pumpon:
high 0 'turn on pump
goto main
pumpoff:
low 0 'turn off pump
goto main
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