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How to use 555 to start some circut in delay?

JakubPrazmowski — Wed, 02 Apr 2025 07:34:00 GMT

Ok. I got monostable mode. I am pressing my little button and timer starts rolling. I getting HIGH on output 3 and it last some time. I wonder why how to connect it with some other circut to start rolling just after state from pin 3 will go back to LOW?

I am new in electronic so any help is very welcome. Thank you very much for help.

Jakub

RE: How to use 555 to start some circut in delay?

jc2048 — Wed, 02 Apr 2025 15:26:54 GMT

The datasheet for the TI NE555 gives this for a sequential timing circuit.

Have a look at the datasheet for the output waveforms and more details.

www.ti.com/.../NE555

They've used a cap and resistor as a differentiator between the stages. If you've got an oscilloscope, it would be worth slapping it together on a
breadboard and looking at the waveforms. If not you could try a simulator.

One question you might ask yourself is, how is it safe to use the differentiator like that, given that it will produce a positive spike on the
other edge (that would take the TRIG input above the supply)?

RE: How to use 555 to start some circut in delay?

dougw — Wed, 02 Apr 2025 14:24:50 GMT

You can use a dual 555, which would be a 556. The first monostable triggers the second monostable to start after a delay.

RE: How to use 555 to start some circut in delay?

JWx — Wed, 02 Apr 2025 10:01:37 GMT

it depends on the exact use case - would it be an one-time delay after power-on? or a delay after button press? what would be an default state of output (for example: default low, goes high after defined time from button press and stays high forever/for defined time/until some other action)? There are many such circuits when searching for "555 delay timer" on the Internet with different schematics for different use cases...

Analysis of a 555 circuit design, will it work, maybe there is a better way

colporteur — Fri, 20 Sep 2024 15:58:11 GMT

I'm looking to build an End of Train (EOT) circuit. The model railroad folks I hang out with, just purchased a commercial unit. After gagging at the price, I figured why not build one.

My search found this resource https://techlib.com/area_50/Readers/Lennie/End%20of%20Train-1.pdf complete with PCB. Unfortunately all the links are dead so I had to generate a schematic from the PCB layout.

Question: Will the circuit work? Are there any reasons for the design?

Instead of bread boarding the design I figured the folks that hang out here are great and offering solutions. Tapping into the experience of the members surely helps. Nothing like experience to find a solution fast.

I have some concerns with the circuit. I couldn't found a 555 circuit that uses pin 7 as an output. I took a look through Cabe Force Essential 555 IC book (Cabe hangs out here:) and found nothing like this beast.

I'm not sure of the design. It looks like nothing I have found.

I'm thinking it would have been easier to just start from scratch.

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

beacon_dave — Sun, 22 Sep 2024 12:10:20 GMT

[quote userid="37381" url="~/technologies/555-timers/f/forum/55119/analysis-of-a-555-circuit-design-will-it-work-maybe-there-is-a-better-way"]I'm not sure of the design. It looks like nothing I have found.[/quote]

Looks like it has been taken from the left half of this bipolar LED driver circuit:

https://web.archive.org/web/20140910104816/http://home.cogeco.ca/~rpaisley4/LM555.html#15

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

aswinvenu — Sun, 22 Sep 2024 06:41:57 GMT

Pin 5 is the Control Voltage (CV). Internally this voltage is generated using a voltage divider. Adding a capacitor will help to produce more a stable control voltage. Good practice is definitely to use the cap.
The design I shared use the same Resistor R2 for both charging and discharging the Cap C3. If you search for astable multivibrator using NE555 you can find design using two resistor solutions as well.

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

jc2048 — Sat, 21 Sep 2024 22:09:19 GMT

The constant is ln(2).

The 2 comes from the relationship between the switching thresholds. When charging, the lower threshold is twice as far away from VCC as the upper threshold. When discharging, the upper threshold is twice as far away from 0V as the lower one. The natural log is involved because the charging curve is exponential in shape.

If you want to delve down further, and work it out from first principles, you'll need to read up about RC time constants, and more generally about circuit analysis.

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

beacon_dave — Sat, 21 Sep 2024 21:04:32 GMT

Looks like some have air generators to recharge the battery amongst other tech...

https://assets.new.siemens.com/siemens/assets/api/uuid:12efd9a7-8e67-4023-bb3a-61f0e450f90c/sie-bro-end-of-train-brochure.pdf

It's gonna be tight to fit all that on a PCB the size of a NE 555 D SMD 🙂

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

shabaz — Sat, 21 Sep 2024 20:59:16 GMT

Ah, good to see. I watched the first couple. Looks like they exhibit a low duty cycle (or perhaps it changes for different events).

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

Jan Cumps — Sat, 21 Sep 2024 20:51:52 GMT

I read the specs, and that's true. They usually run on a battery, and have a light detector to save energy.

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

beacon_dave — Sat, 21 Sep 2024 20:23:05 GMT

I think there is a photocell that only turns them on in low light

https://youtu.be/fE9Y2Pqdwig?t=8

https://youtu.be/LJ_kQLihI3k?t=147

https://youtu.be/d1CnNQ97qKo?t=21

https://www.youtube.com/watch?v=lc_DuOgA5vM

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

shabaz — Sat, 21 Sep 2024 20:05:10 GMT

(I mean on a real train! : )

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

Jan Cumps — Sat, 21 Sep 2024 20:03:29 GMT

Once, while driving through Antioch, Illinois, I had to wait for a big looooong freight train to pass by.
If only I knew that this device was used then ...

It's not used over here.

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

beacon_dave — Sat, 21 Sep 2024 19:56:03 GMT

[quote userid="123345" url="~/technologies/555-timers/f/forum/55119/analysis-of-a-555-circuit-design-will-it-work-maybe-there-is-a-better-way/224198"]Surprisingly difficult finding a YouTube video showing that device blinking.[/quote]

https://youtu.be/SrYin24eBmc?t=411

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

shabaz — Sat, 21 Sep 2024 19:50:13 GMT

Surprisingly difficult finding a YouTube video showing that device blinking. Watched a couple of instructional videos explaining what it does, and I've learned how to install it however 🙂

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

Jan Cumps — Sat, 21 Sep 2024 19:48:44 GMT

I'm an HO fanboy 🙂. As child, I had Jouef trains.

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

beacon_dave — Sat, 21 Sep 2024 19:47:20 GMT

[quote userid="123345" url="~/technologies/555-timers/f/forum/55119/analysis-of-a-555-circuit-design-will-it-work-maybe-there-is-a-better-way/224191"]I suspect train enthusiasts do want it to be close to reality[/quote]

The real ones appear to also monitor brake line pressure and use wireless telemetry to send this information back to the lead engine. Oh, and they are battery powered in a self-contained portable unit. 🙂

I hope this model railroad isn't N-gauge !

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

Jan Cumps — Sat, 21 Sep 2024 19:01:36 GMT

I think that the timings on the schematic are based on the circuit components, not on the regulations of USA train companies.

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

shabaz — Sat, 21 Sep 2024 18:54:59 GMT

Very useful; indicates that the duty cycle needs to be about 10% at approx. 1 Hz. I suspect train enthusiasts do want it to be close to reality, so that's likely a hard requirement, at least that ballpark anyway.

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

Jan Cumps — Sat, 21 Sep 2024 18:48:24 GMT

If you 'd use dual-side surface mount, this would all fit on a PCB the size of an NE 555 D SMD

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

beacon_dave — Sat, 21 Sep 2024 17:21:42 GMT

[quote userid="37381" url="~/technologies/555-timers/f/forum/55119/analysis-of-a-555-circuit-design-will-it-work-maybe-there-is-a-better-way"]Unfortunately all the links are dead so I had to generate a schematic from the PCB layout.[/quote]

Flashing Rear-End Device For DCC Systems

https://web.archive.org/web/20140926093814/http://home.cogeco.ca/~rpaisley4/FredDCC.html

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

colporteur — Sat, 21 Sep 2024 14:46:01 GMT

I believe the design I was hoping to use was riddled with errors. scottiebabe pointed out the chip position error and your drawing suggests a number of other errors. Pins 6 & 7 are connected to together on the PCB and there is no capacitor on Pin 5. your drawing also increases the filter cap.

I have seen designs were there are caps on pin 5 and some where there are none. What is best practice?

In your frequency formula there is a constant (0.693). I've seen constants in formulas before. I can't recall if they are the same. Where does this constant value come from.

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

scottiebabe — Sat, 21 Sep 2024 12:50:46 GMT

Thanks for sharing, I learned what an End of Train (EOT) circuit is, neat!

RE: Analysis of a 555 circuit design, will it work, maybe there is a better way

aswinvenu — Sat, 21 Sep 2024 11:12:00 GMT

I think what you are looking for is an astable multivibrator.