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What is this weird protoboard resistor strip thing? dumb question yep

  1. Apr 15, 2009 #1
    In my lab we're doing some stuff with logic chips and d-flip-flops and in our kit of circuit components are a couple of these red plastic covered strips that have about 12 pins coming out.

    Their some kind of resistor strip but question is how do you use them? do you just consider each 2 pins as a solitary resistor or...

    the professor told us to use them in parallel and we interpreted it like so (assume that grid is a protoboard and this resistor strip thing is not to scale... its smaller and skinny): http://wolfsfiles.googlepages.com/hmm.jpg
    (we want to limit the power being sucked up by the LEDs)

    Anyways i just want to make sure that is how your supposed to use them. He did say put it in parallel so just checking.... never heard of a resistor you only attach by one lead... ok theirs got to be something wrong with that lol

    O ya while on the topic... we have these 2 chips that have 2 d flip flops per chip, and the q of one is hooked to the d of the other... its to make a shift register... and the leds are hooked in parallel with the output q of those 4 dffs... anyways the class can't get the circuit to work... our volt meter says the output Q of one of the dffs is not over 2.30 volts so the next flipflop is considering it a logic 0... we tried boosting electricity to all the chips to 8 volts but the voltage barely changes like to 2.35 volts.... so what is the problem... is it the chips, or the protoboard or the wires or the new Agilent voltage sources we have doing some current limiting or something... owell so far we spent about 8 hours divided by 2 classes trying to get this to work... and the professor extended the lab to next week for the class (of i think 6 people) to get it to work :P
     
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  3. Apr 15, 2009 #2

    mgb_phys

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    The sil resistor strips generally have a resistor attached to each pin and a common wire joining the other ends of all the resistors one of the ends has a marked pin which is the common wire.
    So there is R between the end pin and any of the others - and 2R between any two other pins.
    see http://hobby_elec.piclist.com/e_resistor.htm [Broken]
     
    Last edited by a moderator: May 4, 2017
  4. Apr 15, 2009 #3

    berkeman

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    On the SIP resistors, they come in several different configurations. You either have to look up their datasheet, or use a DVM to figure out how they are pinned out:

    http://images.google.com/images?sou...istor network&um=1&ie=UTF-8&sa=N&hl=en&tab=wi

    On the DFF circuit, what ICs are you using? Can you post a schematic? If they are TTL ICs, then a low output voltage for a logical "1" is not unexpected. If they are CMOS ICs, the outputs should be rail-to-rail.

    Oh, and if you increased the 5V rail to 8V as an experiment, you most likely blew up the ICs, regardless of whether they are (were) TTL or CMOS. Quiz Question -- why?
     
  5. Apr 15, 2009 #4
    Ok first thanks everyone for info about those inline resistors.

    Now onto the reply. The labmanual (http://coefs2.njit.edu/ECE394/ECE394-V.htm [Broken]) says their TTL D-flip-flops 7474 on the bottom and has this link: http://coefs2.njit.edu/main/datas/74hc74.pdf [Broken]
    It says somewhere in the specs tests at 6V and the teachers advice regarding the voltage readouts for the logic 1 was "increase the voltage a little".. so we did. Thx for the tip thought...i won't go past 5V in the future without checking specs.

    Wow i remember when we killed 2 dffs in one of the first labs... it was just to test that they latched and it was 5V source... and the chips cooked... smoke even lol... we believed the problem their was the protoboard because the new chips we received only got warm, not SUPER extremely hot, but the following week... we got a different board and the circuit (or i should say chip) worked... So ya those are some robust dffs we got... (i tested them while debugging this lab and all functions worked out)

    Anyways their was still apparent logic 1 and 0 values being displayed up unto the point where the class ended (just the SRL shifting behavior wasn't occurring).
     
    Last edited by a moderator: May 4, 2017
  6. Apr 15, 2009 #5
    What is the pin spacing? 0.1"? It looks a lot like a plug-in LED bar graph display. I have usually seen them with 10 LEDs in a row. Does the attached picture look anything like yours?
     

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    Last edited: Apr 15, 2009
  7. Apr 15, 2009 #6
    yes that is a led thing. the pin spacing matches protoboard squares if that's the question. and its not the led thing but the red thing that i was confused about.
     
  8. Apr 15, 2009 #7
    The red thing could be a resistor strip for current limiting the LEDs. I would take an ohm meter and see what the resistors are. There could be one common (where?) and 8 parallel resistors. I will guess about 6 volts/.01 amps = 600 ohms.
     
  9. Apr 15, 2009 #8
    kk. i wont be able to find out until next week lol
     
  10. Apr 23, 2009 #9
    Problem Solved.

    Ok the SIL resistor pack was the one where all the resistors were connected to a common wire... which made it really easy to wire the leds :P

    Also the problem with the odd d-flip-flop behavior is... that theirs a difference between using a switch (like the lab manual asked), and connecting directly to ground. So we had to clock every flip flop manually and that meant pulling wires from 5V to ground manually... but it did work.

    I wonder if theirs a way to use a switch and still get the ground behavior when the switch is off... lol maybe using 2 switches where where you turn one on for 5 volts... but when its off you turn on another switch to connect ground... hmm
     
  11. Apr 23, 2009 #10

    berkeman

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    Sounds like you're wanting to use a SPDT (single pole double-throw) switch.

    And BTW, did you debounce your switches with cross-coupled NAND gates (and the SPDT switches are used here generally)...?
     
  12. Apr 23, 2009 #11
    Ya that SPDT switch would be great. I'll see if the parts guy has it.

    debouncing wasn't an issue because we were clocking manually by hand so their was plenty of time for steady state.

    I wonder if an inverter would consider a floating pin as a logic "0" input. If so then the following might do the same behavior with the stuff we have: http://wolfsfiles.googlepages.com/hmmmm.jpg
     
  13. Apr 23, 2009 #12

    berkeman

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    No, CMOS inputs always need to be driven (or pulled up or down via a resistor). Never leave CMOS inputs floating. There are at least two reasons for this.

    Quiz Question -- what are these reasons?
     
  14. Apr 24, 2009 #13
    hmm the only possibilities i can think of is the cmos somehow getting stuck with both transistors in a partially on state. Another thing is maybe the gate acts as an antenna causing odd switching :P
     
  15. Apr 24, 2009 #14

    berkeman

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    Pretty close. Yes, floating to the middle turns on both sets of transistors, and increases power supply current consumption. And the high impedance can be influenced by stray fields, which can cause the circuit to oscillate and buzz.

    Good answers!
     
  16. Apr 24, 2009 #15
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