Are resistors directional?

[RigidRaider]

Been building a couple of those little electronic kits from Maplins with RR Junior. We always fit the little resistors with the identification stripes sequenced L to R as described in the instructions and against the background on the PCB but the instructions don't warn about polarity like with diodes and capacitors.

Are they directional?

 

[westie101]

Nope!

 

[AdrianUK]

As Westie says, resistors are not directional.

It would be usual, in a production environment, to fit them all the "same way round" to aid with inspection & test - so that the inspector doesn't have to keep turning the board around to read the value!

Adrian

 

[Paul_C]

but the instructions don't warn about polarity like with diodes and capacitors.

And it's only some types of capacitor for which that's important. Electrolytics and tantalum bead types are generally polarized for example, but for many types capacitors, like resistors, may also be fitted either way round.

 

[RigidRaider]

Thanks!

 

[bernardgreen]

There is one situation where a non polarised capacitor may need to be fitted a certain way round. That is in some amplifiers the outer foil has to be connected to the correct node of the circuit. This is to reduce unwanted capacitive coupling of signals from that capacitor to adjacent components.

It is normally only critical when components are tightly packed together on the PCB

 

[ban-all-sheds]

That's easily sorted.

Valve amps with point-to-point wiring instead of a PCB....

 

[Paul_C]

Even then there are some cases where you might want to connect the capacitor the "right" way round for best stability. The old tubular capacitors normally had the leads identified by a band around the casing at the end connected to the outer foil.

 

[davelx]

It's easier to read the value of a resistor if the tolerance bands are on the right . eg Yellow Violet Orange Gold - 47K 5%

 

[Paul_C]

I'm not worried whether reading left to right or right to left, but on some of the modern higher precision resistors with a brown or red 1 or 2% tolerance band it's not always clear at first glance which end is which. Then there are some where the colors used are not as distinctive as they could be, and in less-than-perfect light a dark red band can appear to be brown, or a brown can appear to be black, etc. It's noticeable enough if the result comes out as a non-preferred value, but easy to slip up if not looking closely enough between, say, a 10-ohm and a 100-ohm resistor where the browns & blacks aren't quite as distinct as they might be.

 

[JohnW2]

I'm not worried whether reading left to right or right to left, but on some of the modern higher precision resistors with a brown or red 1 or 2% tolerance band it's not always clear at first glance which end is which. Then there are some where the colors used are not as distinctive as they could be, and in less-than-perfect light a dark red band can appear to be brown, or a brown can appear to be black, etc. It's noticeable enough if the result comes out as a non-preferred value, but easy to slip up if not looking closely enough between, say, a 10-ohm and a 100-ohm resistor where the browns & blacks aren't quite as distinct as they might be.

I agree totally. When I first started looking at these things, 45+ years ago, I did not need to consciously 'read' them - just as with someone who knows a foreign language, Morse code or whatever, I just 'looked at them' and my brain immediately knew the value. These days (and for a good long time), I now have to look and think quite carefully - and, even then, sometimes have to get my meter out 'to confirm'. A little of this is due to decreasing size of components, but most is due to factors such as you mention above.

Kind Regards, John.

 

[Paul_C]

When I first started looking at these things, 45+ years ago, I did not need to consciously 'read' them - just as with someone who knows a foreign language, Morse code or whatever, I just 'looked at them' and my brain immediately knew the value.

I know exactly what you mean. I can still do that when delving into an old radio, despite the resistors having been subjected to 50 years of heat and dust, because the markings still seem to be very distinctive, or easily so after just a quick wipe over if very dirty. It's those shiny new components today which are the problem!

 

[bernardgreen]

It's those shiny new components today which are the problem!

In many cases the markings are only there out of lip service to the small quantity users. So there is no care taken over the colour and placement of the bands. It is simply too much bother ( and expense ) to set up the paint machines properly.

Mass produced and supplied on bandoliers the end user using thousands a day never looks at the colours, they read the label on the bandolier and load it into the automatic board stuffer in the right dispensor.

Board stuffer is the machine that puts components into boards at very high speed, as high as 15 components per second.

In the good old days some components had the value written by hand in Indian ink and then hand varnished.

 

[Paul_C]

In the good old days some components had the value written by hand in Indian ink and then hand varnished.

Still have quite a stash of some of those in the vintage spares box.

 

[plugwash]

It's noticeable enough if the result comes out as a non-preferred value.

Though there are a LOT of preffered values in the E96 series and to make things even more fun some ranges of resistor are sold in both E24 and E96 values.