Since Atlas Instruments EC sensors are expensive as hell, I looked around a bit and stumbled upon this DIY build.
It basically measures the voltage across a voltage divider, with the resistor under test being a DIY probe:
As far as I understand:
Do you think that's usefull in a Reef-Pi vs open water ?
It basically measures the voltage across a voltage divider, with the resistor under test being a DIY probe:
As far as I understand:
- The circuit uses AC excitation (IC1A on the left)
- to drive a voltage divider
- R1,R2,R3,R4 as variable known resistors
- best accuracy with the resistor that's closest to the probe under test
- R5 and R6 as known reference for drift correction
- R8 the probe under test
- Measurement is done with:
- two peak discriminator circuits that measure:
- peak voltage of the excitation at IC1B
- peak voltage of the voltage divider at IC1D
- Both peak voltages are compared in IC2D and amplified at IC2C
- two peak discriminator circuits that measure:
Do you think that's usefull in a Reef-Pi vs open water ?
- It will obviously need good isolation and a lot of testing (especially for safety)
- I think it might benefit from bipolar AC excitation
- Inspired from this approach:
- he uses a power plug as probe, because why not
- I'm thinking about using a TRRS gold plated audio connector. It's :
- chemically resistant
- hopefully watertight (needs testing)
- has short standardized contact spacing
- 4 contacts, the middle two can be used for measuring and the outer maybe for grounding to limit the effects in the water and proximity to other things around.
- when you assume a 1mm contact spacing with values of 100-1000µS/cm you get around 10kOhm and 100kOhm which is just in the middle of the above setup.
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