finding obsolete ICs?

Discussion in 'Electronics Resources' started by veritas, Feb 7, 2008.

  1. veritas

    Thread Starter Active Member

    Feb 7, 2008
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    I need some IC's for a project, and I've found several appropriate datasheets for products that would work wonderfully. My problem is every single one of them I've found appears to be obsolete and/or out of production.

    The IC's I need are:
    8x8-bit parallel multiplier
    binary-to-BCD converter

    Does anyone know any places to get obsolete chips cheaply, or maybe even these particular ones?

    My first step is contacting the manufacturers, but so far the ones I've tried have been unable to help.

    Thanks in advance for any help or tips
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    You're as likely to get empty lead frames encapsulated in plastic with the right markings on them as you are to get actual chips. Good luck trying to get your money back from the far east brokers.
     
  3. thingmaker3

    Retired Moderator

    May 16, 2005
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    I'd start looking at the surplus dealers. They often have moderate quantities of obsolete parts in stock.
     
  4. lightingman

    Senior Member

    Apr 19, 2007
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    Hi, Binary to BCD converter.... how many bit's ?...Daniel.
     
  5. nomurphy

    AAC Fanatic!

    Aug 8, 2005
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    Much of the time the through-hole version is obsolete, but the surface-mount version is still available (especially with discrete logic parts). You have to check for newer datasheets and check the package-type coding for the S/M part.

    For instance look for the 74HC147D.
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    They don't have a lot of logic, but check with NTE. Mouser carries some of the line.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Holy cow, is NTE ever expensive.

    If NTE is your only resort, I'd suggest that a redesign is in order.

    If you don't believe me, try pricing LM3914 IC's.

    You can get the original National Semiconductor ICs from Mouser.com and the like for under a buck each.

    Try buying an NTE1508, which is their replacement for the same IC.

    They'll cost you $10 each, at least.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    When the alternative is a warehouse that will take bids on odd lots of the part and has a $500 minimum bid, it ain't all that bad. Scarcity and all that.

    New designs are the way to go.
     
  9. lightingman

    Senior Member

    Apr 19, 2007
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    Hi,This has not answered the question..... Binary to BCD !!!.... The 74HC147 is a one of 10 to 4 bit BCD priority encoder.... Did you need to convert binary to seperate 4 bit BCD outputs....Dan.
     
  10. RiJoRI

    Well-Known Member

    Aug 15, 2007
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    If I recollect, the Binary-to-BCD decoder was nothing more than a PROM; you can either buy an EPROM and program it, or use a tiny microcontroller to do the job.
    You could probably use a couple of EPROMs to develop an 8x8 multiplier. You would effectively be programming a lookup table with the upper 8 bits of the answer in one EPROM, and the lower 8 bits in the other. Or, again, use a micro -- this time with 16 inputs and 16 outputs.

    --Rich
     
  11. lightingman

    Senior Member

    Apr 19, 2007
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    Yep...That's it, that was where I was going to go... The EPROM is the best answer, I have done it this way before and the posts are somewhere on the forum....The original PROM was the 74184 and 74185, but you needed quite a few to go beond 6 bit's and they are rare now....Daniel.
     
  12. veritas

    Thread Starter Active Member

    Feb 7, 2008
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    Thanks for all the responses from everybody. I haven't had time to check out all these resources yet.

    As far as binary to BCD goes, I need to convert 8-bit binary to 2 Decades of BCD. I know this can be done by cascading three 6-bit binary-to-BCD encoders, so that's what I'm looking for.

    IC's I've found that are obsolete are DM8899, as well as a couple others that are equivalent.

    I'll start by looking through the links given.
     
  13. veritas

    Thread Starter Active Member

    Feb 7, 2008
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    A EEPROM would be a great solution to both problems....if the project I'm doing allowed programmable logic. if that were the case, I could easily program a PLD or FPGA with either of those functions as well.
     
  14. veritas

    Thread Starter Active Member

    Feb 7, 2008
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    My goal is to find IC's to conver binary to BCD, and to multiply two 8-bit binary values and get a 16-bit result.

    I was asking about find obsolete IC's because all of the datasheets I've found for either of those functions are out of production and/or obsolete
    The reason I need discrete IC's is because my project has the contraint of using no programmable logic devices, including microcontrollers, EPROMS, PLDs, etc.

    I thank all of you that pointed out surplus suppliers: I am using your advice and digging through the various websites for the suppliers. I will let you know if I find what I need.

    In the mean time please continue offering different suggestions. Just because I provide a reason that I can't use it doesn't mean I don't appreciate the time you took to respond.

    Here are the IC's I've found to be obsolete:
    binary-to-BCD:
    SN54/74185A
    DM74185A
    DM8899


    8x8 multiply
    LMU8U
    LMU08
    MPY08U
    TMC28KU
    ADSP1081

    If you know of a way to acquire any of these, or others that do the same function, for a reasonable price ( < $5 or so), let me know.

    -Veritas
     
  15. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    First, finding those obsolete chips for less than $5 is an additional constraint that may be hard to fulfill.

    Second, the constraints that you mention make this sound like a homework assignment. It is certainly not anything a company would want to incorporate into a project. I have no problem in trying to help on homework, but what work have you already done? Have you reviewed DeMorgan's Theorem and Karnaugh maps? Have you written a truth table for the conversion? If you have access to Horowitz and Hill (The Art of Electronics), those discussions are on pages 491-494. Decoders are on 496-498. Any book that discusses digital electronics must have similar discussions.

    Third, have you considered sequential decoding? That is, go binary to digital and digital to BCD? Here are a couple of links for binary to digital:
    http://pdf1.alldatasheet.com/datasheet-pdf/view/46206/SLS/LS138.html
    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=MM74HC138N-ND

    And here are two for digital to BCD:
    http://pdf1.alldatasheet.com/datasheet-pdf/view/27066/TI/CD74HC42M.html
    http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556595;keywords=74hc42

    The DigiKey prices for the above chips are less than $1 for each chip. Of course, you need to cascade them to get the range of values that you want.

    Fourth, the mathematical operations are covered on pages 497-498 of H&H. There are probably chips available, but I didn't bother to look. H&H uses the 74HC83 and related chips.

    And last, if you are completely lost and would like to see how to do it with discrete logic (e.g., diodes, NOR, and/or inverters, etc.), re-limit the size of your question and one of us might be willing to draw a sample to get you started. From that you could simply expand to the full question.

    John
     
  16. thingmaker3

    Retired Moderator

    May 16, 2005
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  17. lightingman

    Senior Member

    Apr 19, 2007
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    Hi,I have the EPROM code for this, as I have done it before... You need the EPROM (27C32 or 27C64) and a couple of CD4511 to decode the 2 set's of 4 bit's...If you are in need of this code and can program an EPROM then I can send it to you.... If not, P.M me your address and I will put a couple of programmed EPROMS and schematics in the post... Daniel.
     
  18. veritas

    Thread Starter Active Member

    Feb 7, 2008
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    @jpanhalt - Thanks for the suggestions.

    As for point #2, it's not really so much 'homework help' as it is 'senior design help', and it's a small but important part of the project that is being a pain. I worked out the K-maps for the "shift and add 3" BCD conversion algorithm, and it turns out I would need 27 different IC's to get the 6-bit binary-to-BCD that I need. (20x quad NAND, 6x hex inverters, and a quad AND). I think that might put us a little over budget on our design.

    I don't really care to work out any 6-input K-maps -- I don't know if you've had the joy of doing that, but it gets a bit messy with 4 dimensions and all, and doing it 8 times?...no thank you. - are there any solvers on the internet? - an extremely brief search turned up nothing useful for me.

    I've also been considering a decrementing/incrementing implementation using counters, which is a definitely possibility, but the timing hassle that would introduce incorporating into the rest of our design would be tricky.

    I will definitely look at your suggestion for a binary->digital->BCD circuit. I don't immediately see a way to cascade those multiplexors, but I'll have to take a look at that.

    @thingmaker3:
    If you would've pointed me at a place to buy the 74LS192 BCD up/down counter, I would've kissed your feet. The LS193 is just a binary counter, and I have access to those.

    @lightingman:
    Thanks for the idea. If I could use an EPROM I would definitely go for that.
     
  19. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    That certainly sounds like a lot of chips, but the current DigiKey price for the whole lot is <$10.00. 74hc132's are $0.126 each per batch of 25, so you would even have some left over.

    What is your budget for this particular part of the project? If you don't have $10 to spend, it is probably not worth pursuing from any aspect. A single obsolete chip could cost you more than that.

    The number of chips (not gates) is more than I came up with last night for a 3-bit model. I will give it another look tonight.

    John
     
  20. SgtWookie

    Expert

    Jul 17, 2007
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    I actually happen to have a few 192's on hand.
    NTE74192 - LOL! (after earlier bashing NTE for being so danged expensive) but hey, I bought 'em while I was cursing 'em ;)

    How many do you need? Two? Three?
    I would need to test them first, obviously.

    I believe I picked them up about 10 years ago at this store:
    http://www.sarasota-electronics.com/

    Larry is the general manager. Nice guy. He has quite an inventory for a small place. I popped in there a few weeks ago, looking for parts to fix a helicopter. As usual, he didn't disappoint ;) That's also the store where I picked up a couple NTE864s (alt for XR8038/ICL8038, waveform gens) and an ECG892 (XR2206, another waveform gen) - both very tough to find now.

    I also happened to buy a Howard W Sams IC cross reference book at that store; there are a slew of part numbers that are equivalents for the 74192.

    I'm going to take a look to see what other part numbers might match what you're looking for.
    [eta]
    OK, possible substitutes for the 74185A: no listings in the book (lots for the 74182 though...:rolleyes:)
    Larry MAY have those in stock; I don't know.
    Send him a note via the contact info on the page. He should get back to you within a day.
    I'm doubtful on the 8x8, that's pretty specialized. Won't hurt to ask.
     
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