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Stocking a lab = kits & 74xx vs 74LSxx vs 74LVCxx - your input requested. — Parallax Forums

Stocking a lab = kits & 74xx vs 74LSxx vs 74LVCxx - your input requested.

CounterRotatingPropsCounterRotatingProps Posts: 1,132
edited 2009-06-12 03:26 in General Discussion
Am stocking up a·my new lab space for doing general electronics experimenting - you know, your basic Mad Scientist stuff...

I've been looking at Jameco's·parts kits that come with drawer cabinets. They seem diverse and reasonable in price.

1. Do you all know of other/better places for similar kits (beside putting things together from Mouser or Digikey)?

2.·This may seem like an odd question, but I've been wondering if plain-old TTL stuff is still used much (e.g. 74xx) --- every time I go to do something on that level, I seem to need CMOS or 74LSx or maybe the voltage tolerant 74LSVx· series.· The reason I'm asking is that these kits aren't cheap, but I do want to well stock.

* So, if you had a choice between 74x ONLY or 74LSx· which would you prefer?

Or, if that's just a dumb dilema, would it be better to grab a bit of each and make up my own kit?
Please keep in mind this is *general* stuff...

* Do you really still use TTL only much?


thanks for your assistance!
- Howard




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Post Edited (CounterRotatingProps) : 6/11/2009 12:16:42 AM GMT

Comments

  • mikedivmikediv Posts: 825
    edited 2009-06-09 18:04
    Howard I can not speak for what you have in mind only you know for sure, but I do a lot of 5 volts TTL stuff and still use 7400 series stuff and 74LS all the time I just ordered a bunch of 74HC244 and 245 chips
    I guess the question is what do you want to build or learn, the newer low power 3 volts stuff is compatible with the prop chip I use that a lot as well. to better help you give everyone an idea of what you want to build
    or do??
  • kwinnkwinn Posts: 8,697
    edited 2009-06-09 19:32
    Howard, if I had to choose between 74x and 74LSx I would pick the LS.

    Having said that however I must ay that I use 74HCx almost exclusively now. This family operates from 2.0 - 6.0 volts and works well with the old 74x chips. I still service a fair bit of old equipment that was all 74x when new, and have been using 74HCx for several years to replace bad 74x chips without a single problem to date.

    The nice thing about them is they also work with the 3.3V and 2.5V chips without needing a separate supply, and I have used them with a 1.8V chip by having a separate 2V supply for them and using 1K resistors on the signal lines.
  • LeonLeon Posts: 7,620
    edited 2009-06-09 19:54
    Very few people use TTL and LS TTL these days, HC is much better.


    Leon

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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-06-09 20:16
    HCT and LVC are better still for accomodating logic with different Vdd levels. But, yeah, don't waste your money on TTL.

    -Phil
  • jazzedjazzed Posts: 11,803
    edited 2009-06-10 02:42
    Some HC/HCT parts get really slow at lower voltages. I would buy LVC ... it's is also less power hungry (at a glance).

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    --Steve


    Propalyzer: Propeller PC Logic Analyzer
    http://forums.parallax.com/showthread.php?p=788230
  • CounterRotatingPropsCounterRotatingProps Posts: 1,132
    edited 2009-06-10 23:26
    Thanks folks for confirming this.

    not doing much repair work any more (unless I've designed it wrong [noparse]:)[/noparse] --- it looks like I'll be grabbing an assortment then·of HC, HCT, LVC, and LS.

    > Some HC/HCT parts get really slow at lower voltages.

    Steve, as I'm uncertain how that might affect things, can you give a specific example, please?

    cheers
    - Howard

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    No matter how much you push the envelope, it'll still be stationery.
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2009-06-10 23:53
    Since I can get any standard logic part overnight it doesn't make any sense to stock these parts but I certainly would not be using any TTL parts. HCT parts can run at 5V and still recognize anything above 2V as a logic high from the Prop running at 3.3V whereas HC requires a minimum of 3.6V so it won't work. The LVC parts are great as they can run at a lower voltage and still accept 5V input but they cannot run at 5V thus limiting their use.

    ACT are similar to HCT but give you high speed and are able to drive heavier loads.

    Here's a link I came across with a guide to some logic families

    www.maagtechnic.ch/public/pdf/ev/Logik_ICs/Complete_CMOS_Logic_Source_Selection_Guide.pdf

    As to speed, well it's true that some of these parts run "slower" at lower voltages but normally that is never ever a problem.

    My overall recommendation based upon interoperability and availability etc is the HCT series.

    *Peter*
  • CounterRotatingPropsCounterRotatingProps Posts: 1,132
    edited 2009-06-11 00:09
    Peter, thanks for your insight and the link --- I will study that.

    [noparse][[/noparse]EDIT: excellent overview - especially the way the tables cross reference --- also a great example of superior documentation, IMHO]

    Having stuff stocked up is good for lazy, but spontaneous, types like me. [noparse]:)[/noparse]

    - H

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    Got Electrons?

    Post Edited (CounterRotatingProps) : 6/11/2009 12:14:25 AM GMT
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-06-11 04:38
    Peter,

    One minor correction: the 74LVC parts can run at a 5V Vdd. They're rated up to 5.5V.

    -Phil
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2009-06-11 05:11
    Yeah, I know the NXP parts are rated for +5V supply operation but most of the other manufacturers seem to only spec 3.6V max operating. The absolute max rating of these devices is normally over +5V but there is a caveat in the spec sheets which basically says "Truth table guaranteed: 1.2V to 3.6V", go figure. If you can get Philips/NXP 74LVC parts then go for it I reckon.

    *Peter*
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-06-11 06:29
    Peter, you just about gave me nightmares! I've been using TI's 74LVC parts with 5V Vdd and had to go back to the datasheets after reading your post. Well, TI's 74LVC parts also work with Vdd to 5.5V.

    Phew! smile.gif

    -Phil
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2009-06-11 06:50
    Phil, you haven't woken up yet, there's more to come. The TI datasheet definitely says 3.6Vmax for OPERATING voltage. There is a 7V absolute max which is not for operating. The only 5.5V spec I am aware of is the max operating input voltage (not supply voltage). Freddy's knocking at the door....

    TI LVC
    Table 5: Recommended Operating Conditions
    1) Truth Table guaranteed: 1.2V to 3.6V
    2) VIN from 0.8V to 2V at VCC = 3.0V

    Table 6: DC Specifications
    Symbol Parameter Value Unit
    VCC Supply Voltage (note 1) 1.65 to 3.6 V
    VI Input Voltage 0 to 5.5 V

    *Peter*
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-06-11 07:01
    Peter,

    I don't know what part you're looking at, but the TI parts I use (e.g. 74LVC1G14) definitely spec a high-end operating voltage of 5.5V.

    -Phil
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2009-06-11 07:24
    I looked at quite a few parts but it seems the single gate versions (or some) might support 5V supply operation. The SN74LVC14 standard 14-pin pack is 3.6V though.
    I'm thinking the OP is after standard stuff, even DIP.

    *Peter*
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-06-11 08:05
    Hmm, that's just weird: same logic family, same manufacturer, different characteristics. I suspect the TinyLogic parts are a newer design and that they weren't selling enough of the multi-gate chips to make ia process upgrade worthwhile.

    -Phil
  • CounterRotatingPropsCounterRotatingProps Posts: 1,132
    edited 2009-06-11 14:29
    > that's just weird

    Imagine how I feel about this - you guys have been using this stuff a while, whereas I've been out of the industry for some time, and knew I could count on you all to help me sort this out. It looks even more confusing now than before --- just kidding :-P Well, sort of:

    Peter, Phil - I've been doing some pricing. The same chip and package, Jameco might offer for say $0.40, but Digikey has it for $1.20... I just assumed that Jameco is selling overruns, but with your recent exchange, I'm now wondering if the differential is really due to the quality of components (or LACK thereof??).

    What's your insight here?

    thanks,
    -Howard

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Got Electrons?
  • jazzedjazzed Posts: 11,803
    edited 2009-06-12 03:26
    Fascinating how the effects of voltage on time doesn't matter. An example 74HC573 propogation delay tPHL/tPLH from Dn to Qn at 4.5V is typ/max 18ns/30ns. The 2.0V spec is 50ns/150ns (3.3V operation is unknown) ... that scares me since I have typically 50ns after setting an address before output when the device is transparent. That is important to me especially with slow SRAM. I guess the doctor's advice applies "If it hurts when you do that, well, don't do that" [noparse]:)[/noparse]

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    --Steve


    Propalyzer: Propeller PC Logic Analyzer
    http://forums.parallax.com/showthread.php?p=788230
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