Doubt about a capacitor used in severino

Other Hardware 3rd Party Boards
1

Hello,

I am building a severino and it is almost done. I have a few quick questions. :cold_sweat:

The capacitor C9 of 10uF is shown in the Schematic as polarised electrolytic with positive terminal grounded (???) but in the mounting diagram and part list it is specified as non polarised electrolytic.

Q1. Which one is correct?
Q2. What is that capacitor doing?
Q3. How much deviation from the 10uF value do you think is allowable as I could not find non polarised electrolytic caps anywhere, so if polarised is not allowed I will have to use ceramics or something.

Q4. Can I replace the inductor L1 with just a short?

2

That capacitor is smoothing a negative voltage derived from incoming signals on the RS232 connector. If you use a standard polarised electrolytic, then positive to ground is correct. I think the reason they specified a non-polarised electrolytic is that in the absence of a suitable signal on the connector, it can end up getting biased the other way round. The value should not be critical, although if you make it much lower than 10uF then the RS232 i/o may not work at low baud rates. Non-polarised electrolytics are commonly sold for use in speaker crossover networks. People sometimes substitute two polarised electrolytics of double the value connected in series back-to-back.

You can replace L1 with a short, although you may then get some noise on the analogue reference, so your analogRead() calls may return slightly less consistent results.

3

I will try to search for the non polarised one once again and if I cannot find I will go with your double polarised tip.

And I found a 100uH in my old broken printer :slight_smile:

Thanks for the help :slight_smile:

4

You can get 10uF as a ceramic capacitor if that's easier to find.

5

I went to the last shop I knew around here and could not get 10uf ceramic. I brought two 22uF polar electrolytics and a 100mH inductor.

I guess 10uF is in a very odd range if you are looking for non polars. I didn't see any non polar capacitor above 1 uF.

6

I've never seen 10uF in ceramic. You can get 10uF in metallised film, but they are probably too large to fit on your board. Although my local store (Maplin Electronics) sells 10uF non-polar electrolytics, I would never use them in any of my designs, because I have come across instances of them being unreliable.

7

So finally I have got all the components and I will solder them when I go home. I am placing back to back 22uF polarised caps insted of the 10uF one. Thanks everyone. I'll update you if it goes well