when I put a voltage into analog input 1, I see some of that voltage on analog input 2 and 3 and 4 etc....
I'm looking for a solution to get rid of this excess float over voltage when nothing is connected
meaning if nothing is connected, it should read 0 volts instead of partial voltage of the input before it....
and telling somebody to just ignore it or to ground that input is not an option
The analog input must be connected to a source with impedance or resistance to ground of 10K Ohms or less. Add a 10-100 nF capacitor to ground if the source resistance is higher than that.
When switching channels, many people read the new channel twice and ignore the first reading.
most of these inputs will be getting a 0-5v pressure sensor connected to them
if nothing is connected, it should read 0 volts instead of partial voltage of the input before it.
If nothing is connected it will read whatever random voltage it picks up from it's surroundings. Not connected is not 0V. Only 0V is 0V and to see that there must be a connection to 0V.
There is no point in reading unconnected inputs.
jremington:
There is no point in reading unconnected inputs.
there is if you have multiple friends who will be getting the same device from you to use and you dont know how many of the analog inputs they will use in total... and they dont even know exactly how many of those inputs they will use at the moment either....
1 program suited for all users...plug and play...sending all input values over CANbus to another device
jremington:
There is no point in reading unconnected inputs.
Random seed?
scottydoodah:
there is if you have multiple friends who will be getting the same device from you to use and you dont know how many of the analog inputs they will use in total... and they dont even know exactly how many of those inputs they will use at the moment either....
1 program suited for all users...plug and play...sending all input values over CANbus to another device
Then you have to either have a means to tell the program which ones to read or a means to deal with readings from unconnected inputs.
PerryBebbington:
Then you have to either have a means to tell the program which ones to read or a means to deal with readings from unconnected inputs.
I mean...
thats exactly what I am trying to do
the response of the 10nf capacitor sounds like the best option to me... easy enough to implement
To be clear what was described a capacitor on the pin won't solve the problem, a capacitor is open circuit to DC, it won't hold the pin at 0V. What it will do is make whatever reading is taken more reliable and consistent if the source impedance is high.
Tell your friends to wire unused inputs to ground.
My suggestion for the capacitor is intended only for inputs connected to sources with impedance higher than 10K.
What kind of voltage sources are allowed to be connected? I have in mind to apply pull down resistors to all analog inputs. My questions is what resistor value would work.
Railroader:
What kind of voltage sources are allowed to be connected? I have in mind to apply pull down resistors to all analog inputs. My questions is what resistor value would work.
as an example...
my typical use is something like an SSI stainless pressure sensor
0.5v-4.5v
0-100 psi
basically, anything 5v or less is acceptable input to it
Could You post a link to the data sheet of a such a sensor?
The issue I want to avoid is that this extra pulldown resistor affects the signal to be measured and give false, lower values.
attached are 2 image files showing what I am seeing on the outputs...
I am only connected to input 1 right now (pin A0)
using a potentiometer as a test
you can see that when its at 0v, the rest still show floating voltage
and when I put 5v into the input, all inputs are seeing voltage as well
other inputs follow whatever Is in a previous input minus a small amount unless a load is connected to them
Yes, that’s exactly what is expected. So you have a board that may or may not have something connected to an input. That sounds like you have a terminal strip or some means of connecting the optional channels.
Install a jumper wire on all unused inputs. Either you or the end user. There is always a price to be paid for flexibility. Have you ever heard the phrase “there is no such thing as a free lunch”?
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