Schematic reading capacitor values

Question

I've got a schematic that i found on the internet. The schematics is for a solar pwm charger designed around a microcontroller in this case a arduino.

The problem lies in the values for the capacitors they are confusing to me.

The following is what i made out of it:

Non Polarized:

• 2 47nF
• 1 1µF
• 1 220pF

Polarized:

• 1 4.7µF
• 2 1µF

Is this correct and why did he label values this way, did he use some sort of standard or is it purely random?

(for example why dus he sometimes use 1µF but in other parts 1000nF, use 47n instead of 47nF or use 4µ7 instead of 4,7µF)

Answer 1

In your circuit, the only two critical capacitors are those at the output of the LP2950 voltage regulator: C4 and C5.

For all others you can pick whatever you want: I'd probably go with electrolytics for any polarized and cheap X7R ceramics for the rest.

For the two output capacitors of the LP2950 there is an entire chapter in the data-sheet: http://www.ti.com/lit/ds/symlink/lp2951-n.pdf Check chapter 9.2.1.2.1

Long story short: Use a low ESR electrolytic capacitor for C4, rated at at least 10V. C5 must not be a ceramic as explained in the data-sheet so I'd either use a high quality electrolytic capacitor or just leave it out it doesn't seem nessesary at all.

(for example why dus he sometimes use 1µF but in other parts 1000nF, use 47n instead of 47nF or use 4µ7 instead of 4,7µF)

He's using short form notation and hints. If you have a capacitor labled 47n the Farad unit is implied because it is a capacitor. 4µ7 is shorter to write than 4.7µF. It takes less space in the schematic and on a PCB silkscreen.

You'll also sometimes see capacitors values as .1µ or .1u which is the same as 0.1µ or 100n. Again it takes less space on the schematic.

The 1000nF is the same value as 1µF, but it gives a hint that a ceramic capacitor should be used here because ceramics have for a long time not been available in the µF range. You won't see this kind of hints often though.

Answer 2

Remember, many of those who use arduinos are hobbyists, and while some of them are good electrical engineers, others are less experienced and might not produce great schematics.

Firstly, you have correctly read all of the values. There are several different ways of labelling capacitors, and there are no hard and fast rules. It would be nice if the schematic-drawer had picked a style and stuck to it, but that doesn't always happen.

• Sometimes you see ceramics as 1000nF and electrolytics as 1uF because ceramics are usually smaller capacitances than electrolytics. So ceramics are often measured in nF and pF, where electrolytics are measured in uF.
• 4.7 microfarads can be written as 4.7uF, 4,7uF, 4u7, 4.7u or 4.7µF, it's just a matter of style (and nationality, when using , or . for a decimal point). The advantage of 4u7 is that you're unlikely to change 4.7 to 47 by losing a decimal point in the photocopier. The F is superfluous as the symbol tells you it's a capacitor, so leaving it off saves some space.

Also, the symbols used don't necessary mean ceramic and tantalum capacitors. They just mean unpolarised and polarised. Unless the schematic says so somewhere, you can use electrolytics instead of tantalum (and in this particular case that will be just fine). Similarly the unpolarised ones could be any one of a dozen types - but ceramic is probably the cheapest and easiest.

C4 and C5 are a bit special, but in this case the schematic probably doesn't have all the information it really should have, so maybe check the LP2950 datasheet for details.