I've got an Arduino Uno a few days ago.
I want to use it to both constantly measure the voltage on a galvanic cell(and relay the data to pc using python) while also using it to control an automatic burette using 1V inputs and 5V outputs.
I'm not sure how to get the digital inputs to accept 1V as high and 0V as low, as it seems to take anything below 3 as low.
I'm not sure how to get the digital inputs to accept 1V as high and 0V as low, as it seems to take anything below 3 as low.
"High" and "Low" are digital definitions.
If you read the analog value of an analog input you should get values between 0 and 1023. i.e. With the 1.1V reference, 1.1V (or anything greater) should read 1023. 1/2 volt should read about 465. Zero volts should read zero.
So for example, your sketch can do one thing if the readings are above 500, and do something else, or do nothing, if the readings are below 500, etc.
Okay.
But it is possible to simultaneously measure voltages in the 0-1000 mV range while also being able to read 1V inputs and output 5V outputs?
Before we travel this road too far, tell us: is your burette's interface described in your earlier post, here - Arduino connected to both USB and a device that also provides(low) power?? - General Electronics - Arduino Forum?
If so, then the burette's outputs are open collector outputs. That means that they will present an open circuit when they're high, and a ground when they're low. You have to provide a voltage source and a resistance to the output. When the burette output is low, it will conduct current through the resistance and pull its voltage to ground; when the output is high, it's an open circuit, it doesn't conduct, and the output will be at the voltage source's level. Using an Arduino to read the burette's outputs, it's naturally most convenient to use 5V as the voltage source. The burette outputs will then be at either 0V or 5V, just the way that the Arduino likes them.
The Arduino even has a provision for doing this without connecting a source or a resistance. The Arduino's digital inputs have internal pullup resistors that you can enable or disable under program control. Typically, you'd enable them once and leave them alone after that. You can learn about how to do that from the reference page at arduino.cc: Select Learning > Reference, and see the link for pinMode(). There you'll find a link to a description of digital pins, and a description of how to configure them. If you configure the Arduino's input pins as inputs with pullup resistors, then you can connect your burette's outputs directly to the Arduino pins.
You'll have to connect the grounds of the Arduino and the burette together. You probably don't want to connect the burette's 5V to anything at all, since your Arduino will be powered from the PC. The only way that I can see that you'd be likely to damage something is to erroneously connect an Arduino output to a burette output - if the Arduino output is high when the burette output is low, the Arduino will source enough current to damage itself and the burette. So, be careful not to do that.
The title of this post suggests that you're viewing the burette's outputs as analog inputs to the Arduino. While that's certainly possible, it seems to be the hard way to transfer digital data. I think you'll be happier treating the burette's digital outputs as digital inputs to the Arduino, and, if they're the open collector output described in your earlier post, I think you'll be happier using them at 5V.
Very helpful post!
It's indeed the burette I described earlier.
Strangely enough, measuring the burette's outputs from output to ground yielded a potential of +1V instead of five volts, hence why I'm asking if I can use them for digital inputs.
Second, would it be a wise idea to add some resistors between the Arduino and the burette to limit current- just in case something goes wrong(or a fuse, even!)?
Thirdly, to input something to the burette: as the inputs are inversed (low = active, high = inactive),I would need to connect a (high) input pin directly to ground to activate it.
Is it possible to do this straight through the arduino or I would I damage my IC that way?
I've tried using it to control small relays but that didn't seem to work(voltage too low, presumably).
Open collector - Wikipedia See if that clarifies things for you.
For reference, here's the post that describes the burette's interface: Arduino connected to both USB and a device that also provides(low) power?? - General Electronics - Arduino Forum.
You can put resistors between burette outputs and Arduino inputs if you want. I think that 10K would be fine - that would limit the worst-case current to half a milliamp, and the protection diodes of the Arduino should be able to withstand that. Even so, you should make a sincere effort to avoid connecting outputs together - it's just bad practice. I don't see much of a purpose in putting resistors between Arduino outputs and burette inputs, as the documentation shows that the burette has a resistor in series with its inputs already.
Yes, to drive a burette input to the active state, you'd have to ground it.
Yes, it is possible to do this straight through the Arduino. If you connect it carefully, you shouldn't damage the Arduino or burette, if both are working properly already. I'd stay away from relays for this application - it adds complexity, draws a lot of current, and the relays may not switch fast enough, or their contacts may bounce. I don't see that you need them.
I don't know why you measured 1V on the burette outputs. Maybe noise, maybe leakage. To develop confidence, you might consider connecting something like a 10K resistor between a burette output and ground, and measuring again. I think you'll find either ground, or something quite close to it.