resistors for serial download circuit
- Thread starter rmeldo
- Start date
BeanieBots
Moderator
It's not a very critical value. I'm sure 7k9 will be fine.
Please tell, where on earth did you get 7k9 from? A most obscure value.
FWIW, I never let my 10k drawer get below 20. Possibly the most commonly used value.
Please tell, where on earth did you get 7k9 from? A most obscure value.
FWIW, I never let my 10k drawer get below 20. Possibly the most commonly used value.
Buy some bulk 1k, 10k and 100k. Then grow your resistor collection from there. I just got to the Holy Grail of resistor collections after 20 years - parts drawers with one drawer per value. Have just purged some of the really odd mixed bag values I got as a kid and now realise I'm never going to use...
BeanieBots
Moderator
It might measure 7k9 but what is it marked as?
Maybe 7k5 or 8k2??
Maybe 7k5 or 8k2??
westaust55
Moderator
7.9kOhm could be an 8.2kOhm resistor which is very close to the 5% tolerance limit. 8.8k - 5% = 7.79k.It's not a very critical value. I'm sure 7k9 will be fine.
Please tell, where on earth did you get 7k9 from? A most obscure value.
FWIW, I never let my 10k drawer get below 20. Possibly the most commonly used value.
Would be even be slightly out of spec on 5% tolerance is supposedly a 7.5k resistor (7.5k +5% = 7.85k)
The "Lucky Dip" bag might explain the reason - bulk el-cheapo's ?
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Amen, BB, a handy size. In fact, when modding a RC transmitter that did not have end point adjustments (EPAs) to fit a specific ship, I replaced the 16.8k potted joystick (acting as a voltage divider) with a 20k slide pot. To restrict the servo to the range desired, made a quick guess that 10K should be close (well, actually tried it out with another pot as a variable resistor to find the basic "range"), and it seemed 10k would bet me pretty close, so I tried them. Turned out to be dead-on perfect! Of course, this was one part good guessing and 99 parts luck (or a case of the Good Lord looking out for fools like me and granting a small miracle), but, regardless of the explanation, the 10k was handy and worked a treat. And, for tying pins high, etc.It's not a very critical value. I'm sure 7k9 will be fine.
Please tell, where on earth did you get 7k9 from? A most obscure value.
FWIW, I never let my 10k drawer get below 20. Possibly the most commonly used value.
I try to keep several 330R, 1k, 10k, 100k, 2k2, 22k 220k, and 4k7 as the minimum in my little Picaxe playbox (a large fisherman's bait box with breadboards, a multitester, couple o' battery packs, various actives and passives, and, of course, picaxes).
Cheers,
Wreno
I really don't know. The resistors in that bag have a lot of lines on them and the background color choice is pretty poor. I gave up trying to interpret them and I have resorted to measuring them.It might measure 7k9 but what is it marked as?
Maybe 7k5 or 8k2??
As I said i will buy a selection on my next order to rapid or equivalent.
a question I have is on the physical size of the resistors. there are small and bigger ones. I have in the back of my mind that size=power rating, with normal size being for 1/2 watt.
BeanieBots
Moderator
That's actually a tough one rmeldo.
Early carbon resistors could be 20mm X 5mm and only good for 1/4W.
Newer metal film resistors can be 5mm X 2mm and good for 1/2W.
Would need to actually see it to make an educated but still a guesstimate of it's rating. As a general guidline, bigger = more watts but not always.
@Westaust,
Could be well in spec for either value. Many resistor ranges are +/-10% or even +/-20%.
Might even be an E96 range and be within 0.5%.
Also, tollerance of meter???.
Early carbon resistors could be 20mm X 5mm and only good for 1/4W.
Newer metal film resistors can be 5mm X 2mm and good for 1/2W.
Would need to actually see it to make an educated but still a guesstimate of it's rating. As a general guidline, bigger = more watts but not always.
@Westaust,
Could be well in spec for either value. Many resistor ranges are +/-10% or even +/-20%.
Might even be an E96 range and be within 0.5%.
Also, tollerance of meter???.
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Using Ohm equation
Power = V^2/R.
so for Picaxe which works at 5V 1/4 Watt is reached with 100 Ohm, which is a relatively small reistance. That leads me to concluse that for packaging sake 1/4 Watt or even smaller resistors are adequate for Picaxe projects....... but what do I know
Power = V^2/R.
so for Picaxe which works at 5V 1/4 Watt is reached with 100 Ohm, which is a relatively small reistance. That leads me to concluse that for packaging sake 1/4 Watt or even smaller resistors are adequate for Picaxe projects....... but what do I know
BeanieBots
Moderator
Actually, for MOST projects, resistor power rating is not an issue.
More often than not, if you find (or heaven forbid CALCULATE) that a resistor will be disspating power, then step back and ask yourself WHY?
More often than not, if you find (or heaven forbid CALCULATE) that a resistor will be disspating power, then step back and ask yourself WHY?