Guessing which cap is which - Page 1
Forum section: electronics / beginners

author: Stonent
author_rank: Super Contributor
timestamp: October 26, 2013, 11:06:07 pm
content: My capacitor foo is not very good. I'm going to try to build an XR2206 based function generator from a schematic I found that appears to be the very similar to a kit that I saw for saleHere's the schematic I saw online:http://www.instructables.com/files/deriv/F62/I7RL/HAQ2YVGI/F62I7RLHAQ2YVGI.LARGE.gifThe kit schematic was identical except for the addition of a 1n4005, 100uF and 100nF tied from the 12V in to ground.My plan is to build the above schematic but use the additional diode and 2 caps from the kit schematic.The Kit had:1 Medium Sized Electrolytic (Couldn't see value)1 Small Electrolytic (Marked 10uF in the photo of the assembled kit)1 Small Electrolytic (Couldn't see value)1 Tantalum (no value visible)1 Larger box type cap (Grey) (no value visible)3 Smaller sized plastic box type caps (2 Grey, and 1 Red) all the same size (no values visible)What I know from the kit schematic:The 10uF Electrolytic is the amplitude cap.100uF Tied 12V to ground, is polarized (Unknown cap type)100nF Tied 12V to ground, is not polarized (Unknown cap type)Freq range select caps:1uF Polarized (Unknown cap type)100nF Not polarized (Unknown cap type)10nF Not polarized (Unknown cap type)1nF Not polarized (Unknown cap type)Bias/Reference Pin on Chip1uF Polarized (Unknown Cap Type)So I have a small electro, medium electro, a tantalum, and 1 large box cap, 2 smaller grey box caps and 1 red box cap to tie to the above values.Where do you think they would go? A 100uF, 2 100nF and 2 1uF caps, a 10nF and 1nF need to be accounted for.I guess the 100uF would be the bigger electrolytic. Since the 2 1uF caps are polarized. I would assume that would account for the tantalym and the electrolytic but which would be bias/reference and which would be frequency?

author: JOERGG
author_rank: Contributor
timestamp: October 27, 2013, 12:12:41 am
content: Is really nothing written on the capacitors? Maybe this site could help you to identify them.http://www.mds975.co.uk/Content/components01.html

author: Stonent
author_rank: Super Contributor
timestamp: October 27, 2013, 02:10:00 am
content: I would have to buy the kit if I physically wanted to hold the parts in my hand. So I can only go by what I could see.3 Electrolytics, 4 box type caps, and a tantalum.

author: codeboy2k
author_rank: Super Contributor
timestamp: October 27, 2013, 03:25:04 am
content: So you say you saw a photo of the kits with all its parts exploded out on the table, so you don't know and can't know what's what...that schematic is dead simple, you don't need to worry about what you saw, just build it up.The 4 box type caps (grey and red squares) are film capacitors, and they will be the ones used in the frequency selector.The tantulum is probably the 1uF cap on pin 10 of the chip (the Reference BIAS)The small electrolytic is probably a small bypassing cap they used somewhere, I don't see it on the schematic you linked to, but it's on datasheet at the Vcc pin.The medium electrolytic is likely the 10uF between the two 5k resistorsthe 100 uF and 100nF was probably for PSU major filtering, at the input tied to ground.The diode will be first at the input, as reverse polarity protection, and comes before the 100 uF and 100nF filter caps.

author: Stonent
author_rank: Super Contributor
timestamp: October 27, 2013, 05:52:25 am
content: Quote from: codeboy2k on October 27, 2013, 03:25:04 amYeah basically I was needing to know what you just said.Though what threw me was showing the frequency selector with a polarized cap and I didn't think film caps were polarized.Up until now I've only been using electrolytics and ceramics. And when I would look at a schematic, I'd just get whatever the rating was in one or the other. By throwing in film caps and a tantalum I was thinking maybe there was a special reason they needed to be in a certain area or it wouldn't work right or the output would be really dirty.I wonder why they are making it so the diode will short to ground if reverse connected. I would think it would make more sense just to put the diode in series with the voltage.

author: JOERGG
author_rank: Contributor
timestamp: October 27, 2013, 08:40:41 am
content: Quote from: Stonent on October 27, 2013, 05:52:25 amThe disadvantage setting the diode in series is the power loss over the diode and if the diode shortens then you will probably not notice it and have no protection anymore.The only disadvantage setting the diode in antiparallel is that you have to insert a new fuse after crossing the polarity.