MOSFET switch

[Ethan25]

Hi,
I'm planning to integrate my pH sensor and TDS Sensor together to an ESP32 board but I read that both the sensors should not be operated together as the ground looping effect would disrupt the readings. So I'm planning to use a MOSFET in a switch configuration so at a given time only one of them would be on the other would be off.

there were analog isolators available in the market but those are expensive and I think this is a pretty neat alternative ? I would like to know if this a good solution or If my assumptions are wrong anywhere

thanks.

 

[KlausST]

Hi,

as a professional designer ... I´d first contact both datasheets ... to see what signal voltage, current, frequency, waveform ... one has to deal with.

--> I recommend you to do this.

Often a sensor has input, output, power supply.
One needs to find out whether it´s possible to switch only a couple of lines, or all of them, or if swithching is impossible at all.
Also the datasheet tells if there is another option to "disable" this sensor. Like with an ENABLE pin, or using a command via a digital interface.

Klaus

 

[Ethan25]

Hi,

as a professional designer ... I´d first contact both datasheets ... to see what signal voltage, current, frequency, waveform ... one has to deal with.

--> I recommend you to do this.

Often a sensor has input, output, power supply.
One needs to find out whether it´s possible to switch only a couple of lines, or all of them, or if swithching is impossible at all.
Also the datasheet tells if there is another option to "disable" this sensor. Like with an ENABLE pin, or using a command via a digital interface.

Klaus

Hi,
Thanks.

This is from a generic manufacturer so the datasheet was useless there was hardly any information in that.
I was not able to find any option to "disable" the sensor as such, Ig what you're asking me to try is to implement a multiplexer kind of thing using the ESP32 board so I can choose between one of the two.

 

[KlausST]

Hi,

so basically you ask us how to treat unknown signals of two unknown sensors.

No, I did not ask you to try to implement a multiplexer, I asked you to get useful informations first. .. to be able to make a decision.

Btw ... "ESP32" in so far is the only valid information we have, but - in my eyes - has nothing to do with the problem. Or in other words: With any other microcontroller there was the same problem. Correct me if I´m wrong.

Klaus

 

[betwixt]

Note that your original post states there could be problems with ground looping so simply isolating the measurement connection will not fix the problem. Similarly, trying to isolate the ground and power connections too will introduce voltage drops into the measurement. Where ground loops and small signals are concerned, you are probably better off using a multi-pole mechanical relay to switch devices -or- power each device from its own isolated power source and optically couple data to the MCU.

Brian.

 

[barry]

Note that your original post states there could be problems with ground looping so simply isolating the measurement connection will not fix the problem. Similarly, trying to isolate the ground and power connections too will introduce voltage drops into the measurement. Where ground loops and small signals are concerned, you are probably better off using a multi-pole mechanical relay to switch devices -or- power each device from its own isolated power source and optically couple data to the MCU.

Brian.

Why don’t you layout your circuit to eliminate the ground loop?

 

[D.A.(Tony)Stewart]

Analog switches using FETs are simple and cheap to support <50 mA loads
STP cable with a star ground from the ESP32 board eliminates the ground loop. But CM noise from your SMPS will be a problem, so ensure the Shielded twisted pair is connected properly with a single ground connection at one end to the STM32. and consider protected earth PE gnd to 0 Vdc to eliminate CM noise from PS.