Hello,
There are plenty of circuits and tutorials with one sensor used within a voltage divider and a pull-up resistor.
However I haven't seen any tutorial / schematics showing how to deal with several voltage dividers in parallel. Won't the measurement in every divider be modified when the resistance in one sensor changes (for instance with flex or pressure sensors) (see schematics below) ?
Also, is the second schematics equivalent to the first one when it comes to the independance of the sensors ?
The four resistors fed by different digital pins with the digital pins set to LOW when not reading the corresponding analog input. Therefore only the sensor to be digitized is powered.
Solution 1 is OK but when bending one sensor it changes the output on the other ones with a range of a few units, so it might be neglactable in most cases. Inserting delays between measurements did not help, which shows the problem comes from the circuit, not from the multiplexing of analog inputs by the AT328.
Solution 2 works better. When bending one sensor, there's almost no change on the other outputs, even if no delay was used. Of course, it won't function with every kind of sensor because of possible higher current consumption (set the resistor value carefully too). So be careful if you try this solution otehrwise you might fry one pin or the whole processor.
Inserting delays between measurements did not help, which shows the problem comes from the circuit, not from the multiplexing of analog inputs by the AT328.
It shows no such thing.
Read the sensor twice and only use the second reading, that allows voltages to settle, just delaying between readings does nothing.
You will get cross talk on the multiplexer and also all unused inputs should be grounded.
Grumpy_Mike:
Circuit 1 will work circuit 2 is rubbish.
nserting delays between measurements did not help, which shows the problem comes from the circuit, not from the multiplexing of analog inputs by the AT328.
It shows no such thing.
Read the sensor twice and only use the second reading, that allows voltages to settle, just delaying between readings does nothing.
I was doing this double reading actually.
You will get cross talk on the multiplexer and also all unused inputs should be grounded.
In your first diagram (repeated here for clarity) The top rail of each voltage divider is being supplied by VCC. This is surely being supplied by a regulated power chip.
Now even if one of the sensors were to go closed circuit, it's own divider would still have a total resistance of 18K, this is not going to pull down the top rail. So none of the other voltage dividers will be affected.
