Is the capacitor drawn or wired wrongly?

Question

In my recent study of electronics, I chance upon a guide on building a line-following robot. In one of the diagram shown, I realized that the capacitors, namely, C1, C2, C4 and C5, all marked with red arrows, are connected with the wrong polarity. This is from my recent understanding of capacitors. I have listed my observations and reasoning below.

Kindly help verifies if my understanding is correct. I have tried contacting the author but to no avail ;(

My observations:

1. The symbol indicates electrolytic capacitors in use, which are polarised capacitor. The flat side of the symbol should be the positive terminal. However, the curve side(-ve) is connected to the power source(+ve) instead.

2. C3(marked with green arrow) is connected correctly, at least IMO(beginner).

3. I think this is important as the reverse voltage in electrolytic capacitor will cause self-destruction of the oxide layer and fire.

Here is the link to the guide: http://www.circuitstoday.com/line-follower-robot-using-8051-microcontroller

Answer 1

The capacitors marked red are too small to be electrolytic. They must be ceramic. They just used same symbol for all capacitors except without the plus sign.

Answer 2

It's actually a common misconception that the curved side means negative or that the curve signifies an electrolytic. The + sign is supposed to be used to indicate polarity. Any specific meaning of the curved side, if there is one, depends on the situation.

IEEE Std 315-1975:

2.2.1.1B - For style 2, if it is necessary to identify the capacitor electrodes, the curved element shall represent:

a) The outside electrode in fixed paper-dielectric and ceramic-dielectric capacitors;

b) The moving element in adjustable and variable capacitors;

c) The low-potential element in feed-through capacitors. (IEC Preferred)

Answer 3

It looks like lazy symbol use. Those motor noise suppression caps and the crystal caps should be ceramic caps which are non-polarized. You'll have a hard time finding 33pF or 0.1uF electrolytic caps anyways. I don't think they exist.