Sequential LED circuit using LM358 and MOSFETs/BJTs without 555 timer or decoder

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#1 21664602 08 Nov 2012 22:46

elsie li elsie li

Anonymous

Post #1
21664602 08 Nov 2012 22:46

Hi,

May I know how I can build a circuit using LM358 and some MOSFETs or BJTs to sequentially light up a row of LEDs?

Thank you very much.
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#2 21664603 08 Nov 2012 22:57

Steve Lawson Steve Lawson

Anonymous

Post #2
21664603 08 Nov 2012 22:57

What, exactly, do you mean by "sequentially" (sorry in advance if you mean that literally -- it's common on this forum for posters to not know the meaning of the words they use, so it's a necessary question ;)

Can you give me an example of the pattern you are looking for?

Also, is this a one time event, or will it repeat. And how will the pattern transition? All shut off and then sequentially, again, etc.?

And, how about timing? Even timing? How long is the delay between each LED transition? Guess that isn't important in terms of the method, as long as the frequency isn't too high or low.
#3 21664604 08 Nov 2012 23:03

elsie li elsie li

Anonymous

Post #3
21664604 08 Nov 2012 23:03

let say, a row of 6 LEDs, and one will light up after the previous and at the end, all LEDs will be lighted up, then all 6 will blink in unison, until I switch off the circuit.

I have currently a square wave generated from a bistable multivibrator. timing of each LED transition can be 1sec now, for good reference.
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#4 21664605 08 Nov 2012 23:05

Julio Flores Julio Flores

Anonymous

Post #4
21664605 08 Nov 2012 23:05

You could just use a shift register 74HC595. this should work for you.
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#5 21664606 08 Nov 2012 23:05

Steve Lawson Steve Lawson

Anonymous

Post #5
21664606 08 Nov 2012 23:05

Whew...that's going to be difficult to do with the linear components you specified. Much easier with logic components or even better, an MCU.
#6 21664607 08 Nov 2012 23:07

elsie li elsie li

Anonymous

Post #6
21664607 08 Nov 2012 23:07

ya i've seen many circuits online that can work this out, but this is a school project and we are only give opamps, MOSFETs and BJTs to play around with..

Is it possible to have a circuit to light up 3 LEDs first? then i can build on it further... thanks!
#7 21664608 08 Nov 2012 23:18

Mark Harrington Mark Harrington

Anonymous

Post #7
21664608 08 Nov 2012 23:18

Sounds a bit odd this question Steve sequencially hmmm with Lm358 could be possible i suppose but very strange request Normally you would never approach this problem like this You would use a decade counter cd4017 and 555 or these days a micochip or a 7HCT4020 with cmos oscillator as clock source or cd4060

Thats the the way we normally achieve this with fets if you want high current applications
#8 21664609 08 Nov 2012 23:23

Mark Harrington Mark Harrington

Anonymous

Post #8
21664609 08 Nov 2012 23:23

Yes thats possible 3 leds with flip flop and one extra stage in the counter possible

You can form an oscillator from the bjt but why would you if you have a 555 Something doesent make sense here at all in fact if you want the truth I think your teacher is trying to find out whos cheating Thats what this sounds like

An opamp you would use to form eithet a square wave oscillator or sine wave oscillator A bjt gives a triangular waveform and a 555 is either astable, bistable, triggered or pwm modulator

So there is only one answer to this its flip flop using fets with extra stages more or less the same as you would a transistor flip flop with additional stages with feedback
#9 21664610 08 Nov 2012 23:36

Jiajun Chen Jiajun Chen

Anonymous

Post #9
21664610 08 Nov 2012 23:36

How about finding the circuitry of 555 timer and using op-amp and transistor to make a 555 timer?
#10 21664611 09 Nov 2012 00:06

Mark Harrington Mark Harrington

Anonymous

Post #10
21664611 09 Nov 2012 00:06

If you want a really interesting method of achieving this circuit use a ring counter employing ldrs "LIGHT DEPENDENDANT RESISTORS AND LEDS AND FETS"

Here is a link in the meantime for fet flip flops

http://www.techlib.com/electronics/flipflopflash.htm
#11 21664612 09 Nov 2012 00:23

Mark Harrington Mark Harrington

Anonymous

Post #11
21664612 09 Nov 2012 00:23

Here is another little clue for you see attached but you have to think a little bit on this one Think ring counter and think feedback
#12 21664613 09 Nov 2012 01:28

Steve Lawson Steve Lawson

Anonymous

Post #12
21664613 09 Nov 2012 01:28

Weren't me that asked the question
#13 21664614 09 Nov 2012 01:38

Steve Lawson Steve Lawson

Anonymous

Post #13
21664614 09 Nov 2012 01:38

Something like a ring oscillator that sets flip-flops (made out of transistors) ... at least for the first mode, but then, how to get it to switch over to all blinking in unison? I guess the last stage of the ring oscillator could flip the state some how -- perhaps turning on a bistable multi-vibrator that toggles all of the flip-flops at once ... just thinking out loud... well, bed time...

More tomorrow, maybe, unless someone else comes up with something.
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#14 21664615 09 Nov 2012 03:06

Steve Lawson Steve Lawson

Anonymous

Post #14
21664615 09 Nov 2012 03:06

OK, just got back from a nice hot shower. nothing like a hot shower to relax the body and allow the gray matter to work. It's so simple. I was expecting this to be horrendosly complex which scared me away from the simple truth,

Concept attached (left some work for you
#15 21664616 09 Nov 2012 03:14

Steve Lawson Steve Lawson

Anonymous

Post #15
21664616 09 Nov 2012 03:14

BTW: R5 and R7 are there merely because I originally had them driving transistors to drive the LEDs, but then realized I needed some sort of two input gate there, so I decided to make it a "black box" for you to figure out (cuz I'm tired and need to get to bed ;)

Those resistors are inconsequential and depend on the type of logic/driver in the box.
#16 21664617 09 Nov 2012 09:20

elsie li elsie li

Anonymous

Post #16
21664617 09 Nov 2012 09:20

thanks guys! you all have been a great help! i'll work on the few suggestions!
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Topic summary

✨ The discussion addresses building a sequential LED lighting circuit using an LM358 operational amplifier and MOSFETs or BJTs without employing a 555 timer or decoder ICs. The original request involves lighting a series of six LEDs sequentially with a one-second delay between each, culminating in all LEDs being lit simultaneously and then blinking in unison continuously. Suggestions highlight the complexity of achieving this solely with linear components like op-amps and transistors, noting that typical solutions use digital ICs such as 555 timers, decade counters (e.g., CD4017), or microcontrollers. However, given the constraint to use only op-amps, MOSFETs, and BJTs, the conversation explores alternative approaches including constructing flip-flops and ring counters from discrete transistors and op-amps, forming oscillators with BJTs, and implementing feedback loops to create sequential logic. One approach involves designing a ring oscillator to drive transistor-based flip-flops for sequential LED activation, with a bistable multivibrator to switch modes for simultaneous blinking. References to using light-dependent resistors (LDRs) in ring counters and recreating 555 timer functionality with op-amps and transistors are also mentioned. The discussion includes conceptual circuit hints and encourages iterative building starting with fewer LEDs to scale up. Overall, the thread emphasizes the challenge and creativity required to implement sequential LED control using only analog components and discrete transistors without standard digital ICs.
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FAQ

TL;DR: Goal: light 6 LEDs in sequence with ~1 s steps, then blink all together; "Much easier with logic components or even better, an MCU." [Elektroda, Steve Lawson, post #21664606]

Why it matters: This FAQ translates a constraints-only school brief (op-amps + MOSFETs/BJTs) into workable sequencing options without 555s or decoders.

Quick-Facts

Target pattern: 6-LED ramp (1 s per step), then all blink in unison. [Elektroda, elsie li, post #21664604]
Allowed parts: op-amps (e.g., LM358), MOSFETs, BJTs; no 555/decoder ICs per brief. [Elektroda, elsie li, post #21664607]
Clock available: square wave from a bistable multivibrator is already on hand. [Elektroda, elsie li, post #21664604]
Typical alternative if rules were relaxed: CD4017 + 555 or MCU for simpler build. [Elektroda, Mark Harrington, post #21664608]
Shift-register idea (rule-dependent): 74HC595 can step LEDs with minimal wiring. [Elektroda, Julio Flores, post #21664605]

Quick Facts

Target pattern: 6-LED ramp (1 s per step), then all blink in unison. [Elektroda, elsie li, post #21664604]
Allowed parts: op-amps (e.g., LM358), MOSFETs, BJTs; no 555/decoder ICs per brief. [Elektroda, elsie li, post #21664607]
Clock available: square wave from a bistable multivibrator is already on hand. [Elektroda, elsie li, post #21664604]
Typical alternative if rules were relaxed: CD4017 + 555 or MCU for simpler build. [Elektroda, Mark Harrington, post #21664608]
Shift-register idea (rule-dependent): 74HC595 can step LEDs with minimal wiring. [Elektroda, Julio Flores, post #21664605]

What does “sequentially” lighting LEDs mean in this project?

Here, sequentially means one LED turns on after another until all are on, then all blink together. Timing is even, about 1 second per step. The pattern repeats until power off. This matches the described 6-LED ramp followed by synchronized blinking. [Elektroda, elsie li, post #21664604]

Why avoid 555 timers or decoders like CD4017 here?

This is a constraints-only exercise: you were given op-amps, MOSFETs, and BJTs to use. The usual approach would be a 555 clock driving a CD4017 decade counter, but the assignment forbids that to focus on discrete or op-amp design. [Elektroda, Mark Harrington, post #21664608]

How hard is it to do this with only op-amps and transistors?

It’s doable but tougher than with logic ICs. An expert noted it’s “much easier with logic components or even better, an MCU.” Expect more parts and tuning when using only LM358, MOSFETs, and BJTs. [Elektroda, Steve Lawson, post #21664606]

I already have a square wave. Can I use it to step the LEDs?

Yes. Feed your bistable multivibrator’s square wave into a chain that progressively latches LEDs on, then switch to a global blink mode. The 1-second period suits human-visible sequencing well. [Elektroda, elsie li, post #21664604]

Can I prototype with just 3 LEDs first and then scale to 6?

Yes. Build a 3-stage version to validate timing and gating, then expand to 6. Starting small makes debugging current paths and thresholds easier before duplicating stages. [Elektroda, elsie li, post #21664607]

What’s a practical discrete approach without 555/CD4017?

Use a ring-counter-like chain with transistor flip‑flops or FET flip‑flops. Clock it with your square wave, add feedback, and gate the final stage to switch into the all-blink mode. “Think ring counter and think feedback.” [Elektroda, Mark Harrington, post #21664612]

Is there a reference for FET flip‑flops as building blocks?

Yes. A contributor pointed to a FET flip‑flop reference for inspiration. You can adapt the concept for LED-driving gates using your available devices and thresholds. [Elektroda, Mark Harrington, post #21664611]

How do I switch from “ramp-up” to “all blink together”?

One suggestion is to let the last stage toggle a bistable that globally gates all LED drivers. When that bistable is active, the same clock makes all channels blink in unison. [Elektroda, Steve Lawson, post #21664614]

Can I emulate a 555 timer using op-amps and transistors?

Yes. You can replicate the 555’s comparator, SR latch, and discharge transistor with an op‑amp and a BJT/MOSFET. That satisfies constraints while yielding a clean clock or one‑shot. [Elektroda, Jiajun Chen, post #21664610]

What is a bistable multivibrator in this context?

It’s a two‑state circuit that produces a square wave used as your clock. You already have one, so you can drive the sequential logic without adding a 555. [Elektroda, elsie li, post #21664604]

Why do many recommend a CD4017/555 or MCU instead?

Because it’s the standard, simpler solution for LED chasers. As one expert put it, the normal path is a decade counter with a 555, or nowadays a microcontroller. [Elektroda, Mark Harrington, post #21664608]

What’s a shift-register option if rules allow it later?

A 74HC595 can shift in bits with each clock and present 8 outputs. You’d load a pattern that grows lit LEDs, then a full-on pattern for the blink mode. [Elektroda, Julio Flores, post #21664605]

Any edge cases I should watch for when using only linear parts?

Threshold drift and unequal LED currents can stall or skip steps. The expert caution was that achieving this only with linear components is difficult, so design margins matter. [Elektroda, Steve Lawson, post #21664606]

Can you outline a simple concept to start from? (3-step How‑To)

Build a three-stage FET/BJT flip‑flop chain and clock it from your square wave.
Add gating so each stage latches on in sequence, then routes the final stage to a global gate.
Use the same clock to blink all channels when the global gate is active. [Elektroda, Steve Lawson, post #21664615]

What timing should I target for visibility?

About 1 second per transition is readable while debugging and demos. You can scale later, but start with 1 s to verify logic and current handling. [Elektroda, elsie li, post #21664604]

Can LEDs and LDRs form a ring counter variant for this?

Yes. A creative suggestion was a ring counter employing LDRs, LEDs, and FETs. It’s unconventional but satisfies the “no 555/decoder” constraint creatively. [Elektroda, Mark Harrington, post #21664611]

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