This useful cord can allow an Android Phone/Tablet to be used as an osciloscope. All you need is the 4-pole 3.5mm jack to 3 rca cable. The cord will need to be modified and be tested with an resistance meter, so you can figure out which wire goes where. NOTE: EVERY CORD IS DIFFERNET! Also some phones or tablets can be stuborn and only use the cord if theres a load on the left and right speaker pins. Use a 7.5 ohm resistor, wattage shouldn’t matter because headphone standard is 1 miliwatt. The schematic is below:
The only thing bad about this circuit is sometimes series resistances with the signal you’re measuring increase the division.
Links:
4-pole 3.5mm to rca(thus link has changed because All Electronics went out of stock on the other one)
Software
Youtube video(old)
Using a blue box as the case 
Alligator clip to change the division 
110Hz sine wave 
110 Hz square wave 
110Hz triangle wave 
110Hz sawtooth wave 
110Hz reverse sawtooth wave
Circuit Simulator