LM34

Discussion in 'General Electronics Chat' started by R!f@@, Apr 6, 2010.

  1. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    LM34 for USD 31.00 :eek:

    Is it possible to buy this bulky
     
  2. SgtWookie

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    Jul 17, 2007
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    Why not get an LM35? Sure, it's in °C instead of °F, so you lose some precision.

    You haven't mentioned what level of precision you need.

    There's also the LM134, LM334, LM135, LM335...
    Analog Devices has the TMP35, TMP36, TMP37...

    We don't know what you might have access to where you are.

    You might also use a diode as a temp sensor; measuring the difference in Vf when a constant (low) current is passed through it.
     
  3. pilko

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    Dec 8, 2008
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    At Futurlec the LM34CZ is $4.95. the LM34DZ is $1.50

    pilko
     
  4. SgtWookie

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    Futurlec is OK if you don't mind them charging your credit card today, and maybe receiving the parts two or three months from now.
     
  5. pilko

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    Dec 8, 2008
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    I've usually received stock item components in 2 weeks. Although I must admit, other stuff takes much longer. I have complained to their shipping dept --- to little avail.
     
  6. R!f@@

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    My dearest Sgt. :D
    You know I am in the middle of the pacific Ocean, in a tiny sand based land where most of you misses when you fly above.
    But I can get EMS, USPS (Best for me) and whatever. NEVER DHL OR FEDEX , I'm never gonna use them, am still fighting for my samples. I have renewed my import license and paid the import duty ....forget it
    I use paypal to pay, and I am not giving my visa card no. to just any site.

    So that LM34 is for the circuit attached, it seems that L Chung has pushed me again in another yummy circuit project direction and now that I have received a lot of dough from my last job, I am on a spending spree :p.

    I am buying some components online and building all sorts of stuff.
    So guys, what can I use instead of the LM34 and where to get em. I'll buy around 10pc
     
  7. R!f@@

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    Oh by the way Sgt....You never failed to amuse me
     
  8. SgtWookie

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    Maldives - isn't that in the Indian Ocean?

    I don't know; never been anywhere near there.

    OK, well - about the fan speed control. How about if you could get about the same functionality using 1N914 or 1N4148 diodes instead of LM34's?

    Or do you just like to spend lots of money on things?
     
  9. R!f@@

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    AAAAAAh!! Now I have ur attention. Yup .....smack right in the middle of the Indian Ocean or some where?
    Hey...why not they call it Maldivian Ocean !! we are surrounded by it, it's our ocean. India is just aside.....we dominate the ocean.
    A speck in the Ocean ..Yaaaaaaaaaaaay! :D

    No. !!! Tsk Tsk...u missed the best part. :(

    I thought of that but I really never tried it cause diodes are specifically not for temperature monitoring. I did use diodes in the bias stage of an amplifier to sense the output stage heatsink temperature.
    Are you sure that they will perform same way as LM34's.
    If so...I got ton's of it..:)

    about this.... yes and ummmm No!!. It totally depends on my Mood.
     
  10. SgtWookie

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    Well, have you priced LM135/LM235/LM335 IC's?

    They're similar to the LM34's, but output is in °C instead of °F. That means you lose a bit of resolution, but for a fan temp control - how much do you really want to spend on it? And how accurate does it really have to be?
     
  11. R!f@@

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    Sgt.... do you have to be sooooo direct.
    pleeeeeeeese show some humor ......

    The circuit is nothing, it's the LM34 and 1N4001 thing that I like to know
    I'm going to check for LM135/235/335....let me see....
    This circuit thing started because of L Chung, he showed me a electronic load thingy and I browsed that site and got a bit of interested in the low noise fan circuit.
    What I use to have was just a comparator using LM339, which switches between low speed and high speed, when the temp rises.
    So that low noise puuuurrrr fan circuit caught my eye, and since I was going to order some op amps for the load I thought I'll get the LM34's too.
    So there you have it.
    I do have NTC and PTC and plenty of 1N4148 and 1N400X .,. but not LM34.
    I searched and the hit came so high a price.
    So I thought I'll ask my USA buddies to shop for it.
    Ebay is my store... it's cheaper than any other store in this corrupt Place.
     
  12. SgtWookie

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    It's corrupt, and you think I should visit?

    Not sure that I have enough ammunition... ;)
     
  13. R!f@@

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    I'd like that....bring a big one.....when we see it we will just peeeeeeeeeee!
     
  14. SgtWookie

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    Here ya go, Rifaa ... give this a spin ;)

    [​IMG]

    D1 is the temp sensor diode. You could use a 1N4148 or 1N914.
    D2 is the voltage reference. You could use a TL431 "adjustable Zener" instead.

    The idea here is that opamp U1A keeps the voltage across R1, VR1 and R2 constant by sourcing current via D1.

    The wiper of VR1 serves as a base reference voltage that's a bit more than doubled by U1B (at the node labeled Ref).

    U1C sums the outputs of U1A and U1B, amplifies, and inverts the signal. Remember that the diode has a negative thermal coefficient; as it heats up, it's Vf drops. It only changes about 60mV over the 22°C to 42°C range. At the node labeled Out, the signal varies from around 3v when at 22°C to around 8v when at 42°C.

    U1D generates roughly a triangle wave from a bit under 1/3 Vcc to a bit over 2/3 Vcc that gets sent to one input of a comparator; node Out is the other input to the comparator. The output of the comparator drives the gate of a power MOSFET that was chosen for a Vdss of 30v and a low gate charge (9nC) for minimal drive requirements; after all, the 339 has a pretty wimpy current sink capacity.

    I used an LM324 since I figured you had a boatload of them. It's an ancient and slow opamp, but readily available, and it has the ability to sense right down to the negative rail. Nothing needed to be really speedy or particularly accurate in this circuit anyway.

    I haven't built it yet, but might give it a go over the weekend. Instead of using all four opamps, I'll probably use three of them for U1A thru U1C, and use an LM2903 dual comparator for U1D and U2. The only thing I'd have to change would be to use a 1.5k pullup resistor on the output of the comparator when using it as the triangle wave generator.
     
  15. R!f@@

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    OK..
    I'll post back once I construct the circuit and I'll show you.
    Cheers.
    another score for Sgt.
     
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