"The question appears to be, should you connect them? "
Connect what to where? These pins are not connected.
“If I was your teacher, I would subtract half a point for omitting decoupling caps.”
Well, i guess it is a good thing that my teachers are physicists then. There is a saying, when something works don’t mess with it. Listen, i am not being arrogant, or anything. I appreciate your helpful approach. The reason i stick to not using decoupling capacitors is out of fear. I really want to finish with my thesis, and i am afraid adding things to something that works can mess things up.
Especially adding things that i will be adding for the first time in my life.
“I would knock you style points for drawing the symbols for the three ICs in package pin-order instead of grouping pins by function with inputs on the right and outputs on the left.”
What? I did not understand this at all. I created the symbols from the datasheet of the ICs, exactly as they look like.
“BTW, are the 3 ICs really only powered from the coaxial DC jack and not from the Arduino? You should probably put a note on the schematic for the expected voltage input at the coaxial jack. A little documentation with notes also wouldn’t go amiss. I don’t know off-hand what the chips are, but it appears that the U2/U3 block is sensor input (what is the signal protocol back to the Arduino?), but not really sure about U1. Looks to be a quad comparator? What is that circuit block doing? Though I suppose this might be out of context and the circuit is described in the text of the thesis…”
Ah yes, putting a note makes sense. U1 is a chip that contains 4 op amps. U2 and U3 are MUX/DEMUX ICs.
The purpose of the circuit is this:
A resistance goes to where the jumpers are. Since 8 jumper pins, i can read 8 resistances.
The analog circuit does all the reading of the resistance. To be more certain, a square wave is produced by U1 and the surrounding components.
How big is the pulse determines the resistance of the sensor.
The pulse is then fed to an arduino, which measures the width of the square pulse, using timer interrupts.
The purpose of the two MUX/DEMUX, is that each time, the analog circuit measures one resistance, which is specified by arduino, utilizing the two MUX/DEMUX.
The resistances are sensors that we have developed in the lab.
Actually i think the sensors are pressure sensors, we just use common resistances in order to simulate them.
Back to my errors…
I appreciate the help, but i am too newbie to understand your advice.
I get that i should put the NC to all the pins not connected, on the arduino header pins to the right. But what about those that have a name on them like IOREF, +3.3V, +5V, Vin etc?
What do i put on these?
Is it ok if i leave the pins bidirectional?
Should i put only two power tags? One for Vin at the power jack, and one at GND at power jack? Is this correct?