# Multiplexer CD74HC4067 and input voltage question

A multiplexer CD74HC4067 is connected to an esp8266 and distributes the received voltages to the esp8266’s analog pin (see attached) . My questions is: does CD74HC4067 limit (modify) voltages received from sensors before it provides them to esp8266’s analog pin?

Thank you.

Best would be to double check in the data sheet and perform some testing, but from top of head, I think to remember that the switch resistance will be around 100Ω to 200Ω (depends on T° and how you power the device, it’s not the same at 3.3V and 5V) with small variations across channels (but can be a few Ohms - so could amount to 5% of that resistance)

The ESP8266 has a single analog input, with an input range of 0 - 1.0V and If you supply 3.3V directly you will damage the chip. Some boards like the Wemos D1 you pictured have an on-board resistive voltage divider (I think they use 220KΩ and 100KΩ to support a 0 to 3.2V range and convert it to 0 - 1V) so in theory this would need to be taken into consideration as your switch resistance will be in series with then 220KΩ resistor of the voltage divider but 200Ω is small compared to 220KΩ so it should not matter much given all the other errors and %age of fidelity you get along the way.

The analogue input range of a WeMos is ~0-3.2volt, because of a 100k:220k divider on the board.

There should be three resistors, one on each FSR.
None on the output of the 4052, as drawn.

The resistors/FSR should be powered from 3.3volt, and so does the 74HC4052.
Because the ESP8266 uses 3.3volt logic.
Leo…

Thank you All for the clarifications. To implement some kind of over-voltage protection for the wemos, I am thinking of the following setup (see picture). Is this approach right? otherwise, is there any other solution? Thanks.

Completely unnecessary I suspect. Where would this high voltage come from? Follow the advice above regarding resistors and using the 3.3V supply.

Alternatively use an ads1115 module and save some pins.

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To your question, if you power the MUX and the resistive Sensors (with resistor) @ 3.3V you won’t get more voltage back, there is no amplification happening anywhere nor any inductive load. So I’m not sure this is needed (but I’m more of a Software guy)

it seems you are using Grove - Round Force Sensor FSR402 or similar. The resistance depends on pressure applied to this resistor, the greater the pressure, the smaller the resistance. Imagining a huge force would make a very low resistance that would drive a high current draw from your Arduino which you don’t want, so usually there is a resistor in series and deal with the sensor as you would through a voltage divider.

Some kits (like the “official one” from Grove) come with an adaptor which has all the necessary electronics on board

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Hi,
Can you draw your circuit please, pen(cil) and paper would be fine.
And include the CD74HC4067 IC, which is a 24pin device.
CD74HC4067 is a 16ch mux/demux, do you need all those channels?

What is the application, what does your project aim to do?

Thanks… Tom…

Do you mean the wiring between the MUX and the wemos?

Yes and the sensors you have connected to the MUX and how you are powering it ALL.

Thanks… Tom…

The wiring is like in the attached figure.

Sensors are powered from an external power source via AMS1117 that produces 3.3V from 5V. AMS1117 can produce enough current to power the sensors (1A I think).
Measured data are calibrated in the arduino sketch (hard coded) then sent to Domoticz (installed on a PI). In Domoticz I have created some blockly scripts that check the received data and execute some tasks like sending notification emails/telegram or triggering relays to switch on/off ventilation…etc
What kind of sensors do I use? I am still in the testing / validation stage and I have tested a gaz sensor, a temperature sensor (analog), a noise sensor… I even tested a limit switch that detects if a window/door was closed or open.

Hi,
Have you built and tried your project yet?

Tom…

Hi Tom,
Yes I did

and the code is… ?

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