Link an external 6 volts DC to an ARDUINO Analog Input

Hi Arduiners .. Good Evening
I want to link a signal provided by an EXTERNAL DEVICE to an AnalogPin on my ARDUINO NANO ... The external signal is a 6V DC (2 pins) whose Ground I link to the ARDUINO Ground .... I can not find a tutorial how to link this external signal to the three(3) pins ARDUINO has (Sgn / 5V / Gnd),,, ... The Ground for both devices (ARDUINO I know how to do with a Potenciometer .. but not with a complete external signal .... Should be very simple matter .. but I cannot succeed .. PLease help ... Thank you very much indedd ... Regards

You could use a voltage divider with R1 = 3.3k and R2 = 10k, the output voltage would be 4.5V. Do you know about voltage dividers?

Hi Friend .. Yes I know about dividers .... I understand that you are proposing .. But this is not the matter .. The question is that .... for any reason .. I ignore ...When I plug both cards EXTERNAL (5 or 6 volts and Ground) to ARDUINO ... (Signal and Ground ,.. leaving 5V pin from ARDUINO without conection) the level on ARDUINO Analog Input .. goes ALWAYS to HIGH ... indepened of the state of the external signal .... Any voltage or current enters on ARDUINO .. at any time ... I find many TUTOTRIALS and Examples on ARDUINO .. but always refering to a POTENTIOMETER that has not connection at all with another external card ... May you help me ?????

Sorry, but that's not clear...

Anything over 5V damage the Arduino. (Technically you can go Vcc + 0.5V or -0.5V.) That's true even with an "external" voltage as long as there's a common ground.

If you don't have a common ground you don't have a complete circuit and the Arduino can't read it. You'll have a floating-input with unknown/unreliable readings.

And analog doesn't read "high" or "low". It reads between 0 and 1023 (assuming a "regular" Arduino with a 10-bit ADC). If you "force" the analog reading to a binary high or low, any non-zero reading is high.

Hi DVDdoug ... You are rigth ,,, I was saying HIGH or LOW to simplify ... I kown reading 1023 etc... I will explain the difficulty in other way .. First of all .. I can use a potentiometer as shown on ARDUINO example "AnalogInOutSerial" .. and it works fine ... Now .. I disconect the potentiometer and link ARDUINO Pin A03 Ground to Ground on External card .... ARDUINO Signal PinA03 to the 5 volts pin of the External card ... I read the voltages with a "meter" .. and reads correctly when siwtch ON and OFF the external card the voltage goes 5v or 0 ... but the reading of the Signal Pin A03 through the Serial print on the sketch shows all the time 1023 independently of ON or OFF of the external card ,.... Do you have any suggestion ????? Thank you very much indeed ...

You only need TWO connections from the external board, GND and signal. Post a picture of your boards and wiring.
schemeit-project

Hi JCA34F .... Thank you very much .. I shall try tomorrow .. your proposal .... and I shall let you know if I succeed .... Regards