I'm bread boarding a low engine coolant alarm as a demonstration to one of the fitters where I work of picaxe in operation.
The sender (an off the shelf part) is essentially a metallic probe that protrudes into the header tank of the vehicles radiator. The probe is mounted in a nylon fitting that screws into a bush that has previously been silver soldered into the header tank. The header tank itself is grounded to the vehicles chassis while the probe is electrically insulated by the nylon fitting that it is mounted in.
When the radiator is filled the water/coolant act as a conductor between the probe and ground. When the coolant level drops and the probe is exposed the circuit is open.
What would be the best way to monitor the state of the circuit? The simplest way would be to simply treat the probe as a switch that is either open or closed. But then I'm thinking that different coolant/water mixtures might have different levels of resistance, a high resistance might be seen by the picaxe as a open circuit leading to false triggering.
How would I do it with adc so I could add some 'smarts' to the thing with software. Im thinking that one way would be to charge up a electrolytic cap and then read back the charge in the cap with adc. If the circuit was open (because the coolant was low) then the cap wouldn't charge was well. It might charge a bit because of a sheen of water on the surface of the probe.
The sender (an off the shelf part) is essentially a metallic probe that protrudes into the header tank of the vehicles radiator. The probe is mounted in a nylon fitting that screws into a bush that has previously been silver soldered into the header tank. The header tank itself is grounded to the vehicles chassis while the probe is electrically insulated by the nylon fitting that it is mounted in.
When the radiator is filled the water/coolant act as a conductor between the probe and ground. When the coolant level drops and the probe is exposed the circuit is open.
What would be the best way to monitor the state of the circuit? The simplest way would be to simply treat the probe as a switch that is either open or closed. But then I'm thinking that different coolant/water mixtures might have different levels of resistance, a high resistance might be seen by the picaxe as a open circuit leading to false triggering.
How would I do it with adc so I could add some 'smarts' to the thing with software. Im thinking that one way would be to charge up a electrolytic cap and then read back the charge in the cap with adc. If the circuit was open (because the coolant was low) then the cap wouldn't charge was well. It might charge a bit because of a sheen of water on the surface of the probe.