Here i am listing the last few parts in this Interface discussion. Only Points to remember are listed.
Resistors attenuate voltage or reduce. Current flow has to be limited. The adc may get damaged when voltage above Vcc is applied
Let us assume 4v is applied to a voltage divider of 30k first 10k second. 3v drops across 30k and 1v drops across 10k – This 1v sample can be measured
Values like 10k and 30k are non standard and expensive. Use 1% MFR resistors only
You can go upto 1 mega – Beyond that leakage currents cause errors. A DMM has 10 meg input resistance For the same reason. Not to save battery but to avoid loading the point. Being tested
A transistor heats up if it is not fully on or saturated. Ensure it is fully on. – If Vce sat is 0.5 v it is fully conducting — If Ic is 1A and Vce is 0.5 V then heat dissipated is 1 x 0.5 watts or 500mW
Try out and see the current through motor using DMM carefully with a 10 ohm 5w in series. 10 ohm is to protect DMM at 2A range, In case of short circuit, dmm fuse won’t blow. Put dmm, motor and 10 ohm in series.
Knowing Electrical Basics both theory and practical is important to be a good embedded systems professional. Just dont jump into coding and expect to master the Art of Electronics.