Electronic – Capacitors with a “/” on schematic

(1) Does 'input 2' correspond to the +12V wire and 'input 1' to the -12V wire?

NO. This is connected to the power supply connector. (Pin 1 is the positive, pin 2 the ground or 0V). The INPUT connector is where the audio signal goes (2) is the live and (1) is the ground.

(2) When I see the symbol 'ground' on the schematic does that mean that I need to connect those to the -12V line? I have no 0 volt line in the circuit so what is the ground line?

All voltages are relative to each other. If you only have TWO wires from the AC/DC converter then the most positive is taken as the positive and the other one is the OV or ground. A simple check with a voltmeter will determine which is which.

(3) Why are C3, C5 non-polarized capacitors and why are the other ones polarized? The current flows from negative to positive. Does that mean that the polarized capacitors need to be placed with their positive legs pointing to the left?

C3 and C5 are small value capacitors (0.1uF). These can be easily made as physically small, non-electrolytic types. They have the advantage of being able to decouple (short out) the higher frequencies. The larger values (uFs) are made as electrolytics as these can be made with high values in small physical packages. They are generally much poorer at handling the high frequencies. By combining an electrolytic with a non-electrolytic capacitor in parallel (eg C3, C6) you get a much better response over a wider range of frequencies. In this case they are used for 'smoothing' the supply voltage, preventing hum and hiss. The positive plate of an electrolytic is shown as an open rectangle but left and right (or up, down) have no meaning in terms of connection as this will be determined by board layout. Conventionally current is taken to flow positive to negative.

Looks good at a quick look through. Nothing obviously bad.

BSS138 are especially wimpy MOSFETS. Ok for playing but do not do justice to the rest of the circuit. Not up to quad copter use, but, you know that.

DTR is intended to reset the processor I assume.

To pass the Olin schematic test you'd want (amongst other things)

• To move text strings off lines (eg PS3 PS4 by MOSFETs and rotate them to horizontal where sensibly possible. PWM3 label is overwritten by MOSFET name etc. VCC label in eg FTDI box turn 90 degrees.

• Have connectors from FETs vertically above FETs rather than bent at 90 degrees. Vbatt could be above or to one side.

• And similar

Aim is to not 'twist brain' to follow obvious flow.

Some people will read diagrams with small points as above and find them less than comfortable but bearable. Others will essentially refuse to look at them. The latter reaction is somewhat extreme but reflects an underlying semi-reality - a really tidy diagram with attention to layout, text and component orientation, consistent labelling and more SUGGESTS an underlying technical competence, and a messy diagram tends to suggest the onbious. Neither of these impressions may be correct, but they are often a useful starting guide. Also, arguably, a tidy diagram reflects respect for those who you expect to use it (and the validity and relevance this has been argued at length :-) ) and is more likely to allow you to spot technical errors.

NB: DO NOT ever take my diagrams as examples of how to do things well. I am a "classic messy" who attempts to force the world's mold on my output with varying success. Judgements based on normal standards may mislead one wrt the value of a classic messy's offerings - and may not :-). Equally a chronic super-tidy (who can in their own way be just as bad as a messy) may produce superb copy but not always match it with underlying competence. FWIW.