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I'm newbie, thus my simple question. In the schematic below, which side of the capacitors is the positive? Why? Or are they assuming that I have to use ceramic capacitors? Usually my schematics come with a plus sign or an side that is bended, but this one is symmetric.

schematic with capacitors

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  • \$\begingroup\$ In general, the positive side of the cap is the one that is expected to be at a higher potential during circuit operation. That said, 3.3µF is reasonably within the range of ceramic capacitors. \$\endgroup\$ – Andrey Akhmetov Aug 29 '18 at 19:12
  • \$\begingroup\$ There are two types of caps: polarized and non polarized. I have no idea what that circuits is suppopsed to do, but in case the polarity can switch, these are non polarized ones. \$\endgroup\$ – PlasmaHH Aug 29 '18 at 19:13
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    \$\begingroup\$ It's a simple light flasher (bistable) and the collector side of the capacitor would be positive if a polarized capacitor is used. The base side will never be above about 0.7V and the cap will be charged to the supply via the 4.7k Ohm resistor. \$\endgroup\$ – Jack Creasey Aug 29 '18 at 19:19
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    \$\begingroup\$ forum.allaboutcircuits.com/threads/… \$\endgroup\$ – G36 Aug 29 '18 at 19:20
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The 2N2222 base voltage should never exceed about 0.7 volts while the collector voltage could go as high as the supply voltage. In most cases if using a polarized capacitor the positive lead would go to the collector. 3.3uf is fairly large for a ceramic typical max 1 to 2uf, film capacitor go up to 100uf and are non-polarized. Polarized Tantalum up to 470uf and Aluminum Electrolytic Capacitor(Very Large). What you used depended on how stable the frequency requirement. Temperature affects many types of capacitors, electrolytic are usually the least temperature stable device.

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  • \$\begingroup\$ Don't forget about the reduced capacitance due to DC bias...particularly bad (30-50%!) in most types of ceramics. I think electrolytics are much better in that respect. \$\endgroup\$ – DKNguyen Mar 6 at 0:07
  • \$\begingroup\$ Electrolytic capacitors are pretty stable with temperature until you get well below 0°C. Similar to X5R without the often horrific voltage coefficient (as much as -80%) that Toor mentions. \$\endgroup\$ – Spehro Pefhany Mar 6 at 1:12

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