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

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Discussion Overview

The discussion revolves around the use of resistor strips in a lab setting involving logic chips and d-flip-flops. Participants explore how to properly utilize these resistor strips, their configurations, and the challenges faced in getting a circuit to function correctly.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant describes a resistor strip with pins and questions how to use it, suggesting a misunderstanding about connecting resistors in parallel.
  • Another participant explains that the resistor strips typically have a resistor for each pin with a common wire, indicating the resistance values between pins.
  • Concerns are raised about the output voltage of d-flip-flops, with one participant noting that the voltage is not sufficient for the next flip-flop to recognize a logic "1."
  • There is mention of experimenting with voltage levels, with a warning that increasing the voltage beyond specifications may damage the ICs.
  • Some participants discuss the physical characteristics of the resistor strips and their potential use for current limiting in LED circuits.
  • A participant shares that the issue with the d-flip-flops was resolved by understanding the difference between using a switch and connecting directly to ground.
  • Another participant proposes a method to use switches to achieve desired ground behavior in the circuit.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the resistor strips and their configurations. There is no consensus on the best approach to resolve the issues with the d-flip-flops, as multiple factors are considered, including the components used and the wiring methods.

Contextual Notes

Participants reference specific components and configurations, indicating that the discussion is dependent on the particular lab setup and the specifications of the ICs being used. There are unresolved questions about the proper use of switches in the circuit.

Who May Find This Useful

This discussion may be useful for students and practitioners working with logic circuits, resistor configurations, and troubleshooting in electronics labs.

FocusedWolf
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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 you 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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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
 
Last edited by a moderator:
FocusedWolf said:
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 you 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

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?
 
berkeman said:
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?

Ok first thanks everyone for info about those inline resistors.

Now onto the reply. The labmanual (http://coefs2.njit.edu/ECE394/ECE394-V.htm ) says their TTL D-flip-flops 7474 on the bottom and has this link: http://coefs2.njit.edu/main/datas/74hc74.pdf
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 you 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).
 
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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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Bob S said:
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?

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.
 
FocusedWolf said:
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.
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.
 
kk. i won't be able to find out until next week lol
 
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
 
  • #10
FocusedWolf said:
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

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)...?
 
  • #11
berkeman said:
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)...?

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
 
  • #12
FocusedWolf said:
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

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?
 
  • #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
 
  • #14
FocusedWolf said:
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

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!
 
  • #15
thx :P