I have put together a sensor for measuring the level in a sewage holding tank in my boat. I am using strain gauges on the discharge tube to measure the change in hydrostatic pressure in the tank and reading the signals with an Arduino mini. I am using this technique so I can avoid an intrusive sensor (for obvious reasons). So far all is good.
I want to connect the sensor to the onboard resource monitoring system (fuel, battery, water, etc.) which will accept sensors with variable resistance output where 0 ohm is empty and 190 ohm is full. I have looked at digital potentiometers but all that I have found is 100 kOhm which is not useable.
Does anyone have a suggestion for a circuit or module where I can control the resistance from an Arduino in the range of 0 - 190 ohm? I need a resolution of at least 16 steps over the range.
This question has been asked before (of course! ).
And the answer is that however you look at it, the resource monitoring system either puts a resistance in series with the sensor and the supply, or generates a constant current to the resistor - which is not the same as putting a resistor in series.
It however does not matter - in the end, it simply measures - or responds to - the voltage across the sensor, so all you have to do is to generate a voltage which is meaningful to the metering system.
TomGeorge has indicated how to assess how much current you need to control and in the process, you will be able to determine what readings relate to what resistances and corresponding voltages. You then need to arrange a FET to be driven by an op-amp (since you only need to sink current, not generate a voltage as such as the monitoring system does that for you) to match that voltage to the filtered output of your PWM.
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