odd ball parts....

[dacflyer]

looking at the national website i was looking at the LM34 temperature sensor. i was looking at the application pages..and there is a neet looking and simple to make temperature bargraph meter..
only problem i have is...finding the so called
1-2% tolerance 402 ohm resistors.... also i cannot find no one that carrys the LM34 either
any one got these parts or where i can find them with out having to spend a fortune....
i know theres no such thing as a 402 resistor...so i am dure i'd have to put 2 resistors in series...400 + 2 ohms....but where does one find 1-2% tolerance types...

[Chris Smith]

Try digi key and mil specs, but also any resistor may fall right on those numbers any way,... just by luck. Any two that happens to reads 402, is what you want.

[jwax]

If the circuit truly requires 402 ohms, you select a 390 (standard value) carbon, break out your trusty small file, and start swipeing away!
You'll first carve out the body, then when you start cutting into the resistor element, monitor the resistance until you hit 402 ohms. Cover the wound with glue to prevent moisture from shifting its value.
John

[k7elp60]

Jameco.com has the LM34, but you must specifiy the
LM34CZ(-40F to +230F) for $4.90 or the LM34DZ(+32F to +212F) for 1.99.
The 402 ohm resistor is a standard value for 1% resistors.

[Externet]

Hi.
I do have reels of 402 ohm resistors at 1% or better. Surface mount or trough hole ? How many do you want, I can send in an envelope.
Miguel

[Dave Dixon]

Hey,
402 is a standard resistance value. Search
on "standard decade resistance values" for a chart.
I have a few Dale thru-hole RN55D4020F's hanging
around. 402 ohm, 1/8 watt, 1%. Let me know
if you are interested.
Dave

[haklesup]

Choose a handfull of 5% 400 or 410 ohm and start measuring, you will probably find two at 402 before long but...<p>Value is only half the story. Given that it is to be used in a temp sensing circuit, I would expect you would want a resistor with a low Temperature Coefficient so that the value does not stray far as temp changes. If these resistors are used in a matched or differential circuit, you may want to mount them close together to ensure they are at the same temperature.<p>By and large, 1% tol resistors also have low temp coeff. as well.

[Dean Huster]

Digi-Key carries 1% resistors.<p>A word about that file and resistor trick of obtaining oddball values: <p>The history is that it was a popular method of getting weird resistor values (i.e., standard 1% resistor values) from cheap parts back in the 1950s and 1960s when 1% resistors were both hard to find and expensive. I remember that a typical Dale 1% resistor was $1.50 from Allied Radio back in 1966.<p>The first problem with this is that it requires a CARBON COMPOSITION resistor to work the file trick and not a carbon film resistor. You begin with a value that's just lower than the required value and file until you get the value needed and patch the cut with clear fingernail polish. A triangular saw sharpening file worked well for the application.<p>The second problem is that by filing through the resistor, you create a "hot spot". If you operate the resistor anywhere near its maximum power rating, you'll burn it out.<p>The third problem is that of all types of resistors, carbon resistors are the least stable of all and carbon composition resistor are notorious for values that go wacko with changes in temperature or with age. They usually go high in value with either. In most cases, you're trying to substitute for a precision 1% tolerance, metal film resistor that is pretty stable with time and temperature. That filed carbon resistor will probably be off in value when the A/C thermostat kicks on and will certainly be off in value in just a few weeks or months time. File all you want to -- you still end up with a resistor with a 5% tolerance that isn't stable enough for the application you need. It was a cute and handy trick in 1955, but really not worth the time today. <p>Digi-Key has the 1% resisitors as such attractive prices that I always buy a larger pack of resistors (I'll actually buy a pack of 200) even if I only need one so that I can build up my stock of 1% resistors. At 96 values per decade, it takes a lot of money to even buy 10 resistors of each value to have a full complement of resistors for five or six decades. If you needed that particular value once, you may need it again later, so buy several. It doesn't hurt to at least buy several 10.0, 100, 1.00K , 10.0K, 100K and 1.00M 1% resistors just to have on hand since those are very handy values.<p>Dean

[L. Daniel Rosa]

Externet, do you have other values available in 1%? I'm looking to gather the pieces for decade blocks, so I'll need 1.00, 2.00, 3.01 and 4.02 for just about every decade except that I have 10.0k (in rediculous quantity), and can improvise 1.00k and 2.00k. Drop me a PM, okay?

[jwax]

Alright Dean, you've dated me! (as in carbon!)
Filing up carbon comp resistors goes back to the early days, and yes, it does have its pitfalls, drift and temperature instability to name two!
But, in a pinch.......
"Ol' John"

[Dean Huster]

Hey, John. Here's a trivial question regarding filing resistors. Typically, how many did you accidentally snap in half before you got to the right value? That was the part I hated. Eight ohms away, one more pass with the file and <pop!> you had a pair of unodes in your fingers.<p>I did run across a guy that did an entire multi-position switchable "precision" attenuator that way. A year later, he found out that his precision attenuator might as well have been a pot!<p>Dean<p>[ June 15, 2004: Message edited by: Dean Huster ]</p>

[jwax]

Waaay too many, Dean! Same with the "torch-shift" method of changing values! That one "stinks" too! Lots of "Unodes" as you call them.
Those, we'd sell to the freshmen saying they'd be ahead of the class if they brought theirs in instead of having to make them!
"One leaded resistors- get them while they're hot!"
While on the subject of component-abuse, have you ever "adjusted" the natural frequency of a crystal?
John

[perfectbite]

It wouldn't be anything like cleaving diamonds would it?

[dacflyer]

Externet & Dave Dixon >>> all i need is 2 but i'll take 6 or so...<p>on the national site the LM34's application ideas for the bargraph temp meter..its just requires 2 of the 402 ohm resistors...if either one of you like to send me a few of them,,let me know how much or whatever.... reply to dacflyer@hotmail and i'll reply with my address...thanks...<p>
K7ELP60 >>> thanks for the heads up on the different LM34's i like the LM34CZ , but since the project i want to build didn't specify which one to use,, i will go with the CZ version...thanks...

[Dean Huster]

Oh, yeah, John! When I was a Novice ham, I remember reading an article about grinding your own. A piece of plate glass, some Comet, some water, and a lot of patience. I put my hand to a a few times. Like the resistor filing, you could only go up, but not down. Trouble is, those were the days before folks like us could afford frequency counters (the hp 5245L was best on the market back then and totally out of sight on price), so checking the frequency was difficult as it didn't shift that much when all you had was a general coverage receiver to work it against.<p>Wait a minute. Seems to me you could go down a little. Didn't they have you rub a pencil lead on the face or something? But you had to be careful of that or you drop the Q into the gutter.<p>Dean