Greetings:
I am constructing a device to allow me to connect three Tech-Edge Moda capacitive tank sensors to three resistive input ports on a Cerbo GX system to measure the water level in two water tanks and one waste tank on a sailboat.
The Moda’s 1-to-5-volt sensor readings are read by a microcontroller (ATmega2560), then processed by the ADC. The digital outputs are then mapped to one of 8 output pins that activate relays on an eight-step ladder providing steps of resistance between 30 to 240 ohms, structured to provide more readings as the two water tanks get empty (or full in the case of the waste tank). And, although the 8 steps do provide great linearity, they provide enough steps to let me know when the water and waste tanks are getting empty or full in the case of the waste tank.
Based on what I have read, I believe that the Cerbo resistive inputs, when activated, apply 6-volts to the input leads. I assume that the purpose of the 6-volts is to create a small current that is read by the Cerbo and then compared by the Cerbo to an internal resistance. the Cerbo then compares the current generated from the input leads to the internal current generated by the internal reference resistance that determine tank levels and changes in tank levels.
So, here’s where I am looking for help.
- Is my understanding of how the Cerbo GX resistive input work correct? i.e. that the Cerbo GX system applies 6 volts to the input terminal and uses the current generated to measure tank levels?
- Is there a minimum resistance that the Cerbo GX system uses – i.e. is there a base resistance always present on the resistive input of the Cerbo GX system? If so, is it 30 ohms?
- Has anyone had experience building the same kind of device? If so, any suggestions or recommendation? All help and ideas greatly appreciated.
Thank you!
