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#128229 - 10/29/02 11:03 AM Electrical Component Polarities
Gralex Offline
Junior Member

Registered: 10/29/02
Posts: 1
Loc: asd
I'm doing a soldering project for school and I need some info on certain components and how to find their polarities and such.
The parts we're using for the project are:

1uf Capacitor
.01 DIsc Capacitor (103)
555 Timer IC
10K ohm Trimmer
SP2655 Power Transistor
33K Resistor
1K Resistor
75K Resistor

Basically I need to know which of these parts have polarities and how to figure out which way they'd go on the circuit board.


#128230 - 10/29/02 12:51 PM Re: Electrical Component Polarities
SvenNYC Offline

Registered: 08/19/02
Posts: 1685
Loc: New York City
Resistors are not polarized. They can be connected in any direction

I presume the disk capacitor you mention is a ceramic cap. Ceramic caps are unpolarized.

Electrolytic capacitors (unless specifically indicated), however, ARE polarized.

Be very careful to observe polarity on these, or you risk damage to the component and the project at best; and at worst personal injury (overheating and exploding caps).

Transistors are polarized. It depends on the circuit and the transistor. Use a transistor checker.

Good luck. :-)

#128231 - 10/29/02 01:21 PM Re: Electrical Component Polarities
pauluk Offline

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Resistors can be wired either way, as Sven has said. The trimmer has three terminals. Depending upon the style, you'll find that the wiper is either the center of the row of three or the one which is set away from the other two. Reversing connections to the two ends of the track will just affect which way you have to turn it. (In the case of the components you've listed, I'd guess that the trimmer is to adjust the timer delay.)

The 1uF capacitor you're using will most likely be an electrolytic type. If you look on its body you should see that one wire is identified with a "+" or "-" sign. In the case of axial-leaded can-type electrolytics, the negative lead goes straight to the outer metal container. 555 timer projects often specify tantalum bead capacitors for the 1uF range; these are also polarized and should be marked for correct polarity.

SP26555 -- Not a transistor I'm familiar with, but I would guess it's just a general purpose power transistor that you'll be using to switch some load from the timer output. Transistor connections vary considerably depending upon type and case style. If you don't have the correct pin-out (E,B,C - emitter, base, collector) with your project notes, I'll see if I can look it up for you.

The 555 timer is an 8-pin DIP IC with 4 pins down each side. Depending upon the make, looking at the top of the device there will be either:

(a) A small dot beside pin 1, or

(b) A small U-shape notch at one end.

Turn the IC so that the dot is at top left or the notch is at the top, then the numbering goes like this:


That's viewed looking from the top of the device.

Hope this helps.

[This message has been edited by pauluk (edited 10-29-2002).]


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