Square Wave Generator Based on 555 Question. - Page 1
Forum section: electronics / projects

author: JJ_023
author_rank: Frequent Contributor
timestamp: December 31, 2023, 10:38:14 pm
content: So I built on a breadboard a square wave generator based on a 555 in astable mode. The goal was to try to get 5 kHz with as close as possible to 50% duty cycle.Vcc was 5VThe capacitor value selected was 47nF1 of the resistors was 330 ohm. The other resistor was a high quality 10 turn pot from bourns used to fine-tune the frequency.There is also a 330 ohm resistor on pin 3 as a load.There is also a 10nf capacitor on pin 5.I am getting about 800 mV of overshoot at the top of the waveform. Besides that the square wave looks well-formed. What is causing this overshoot and what could be done to correct it.This is nothing more than a learning experience not a circuit for anything in particular at this moment.Scope screenshots are attached.

author: CaptDon
author_rank: Super Contributor
timestamp: December 31, 2023, 11:09:28 pm
content: Almost entirely the fault of breadboard inductance and lead lengths of scope and power supply leads. Not uncommon for bread boarding and often the reason why bread board projects act weird or fail entirely.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: December 31, 2023, 11:12:57 pm
content: Quote from: JJ_023 on December 31, 2023, 10:38:14 pmThe 555 has known high supply current spikes, so needs good supply decoupling.A series R can reduce the overshoot, at the expense of higher drive impedance.You could experiment with ferrite beads.

author: CaptDon
author_rank: Super Contributor
timestamp: January 01, 2024, 02:40:32 pm
content: If you need the squarewave to have as close to 50/50 duty cycle as possible you should double the operating frequency and use a TTL or CMOS divide by two follower. 555 devices don't do 50/50 very well without extra components. With the extra divider stage as a follower it is much easier to trim the operating frequency of the 555 and still get a good squarewave from the divider. That is hard to do with only a 555 and no divider.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 01, 2024, 03:10:38 pm
content: If you're after 50/50 square wave, you might have better luck with this alternative 555 astable configuration, rather than the standard astable configuration.

author: mawyatt
author_rank: Super Contributor
timestamp: January 01, 2024, 03:31:56 pm
content: Agree with CaptDon, following the 555 with a divide by 2 flip-flop (74HC74) gives a very precise 50% duty cycle at lower frequencies regardless of the 555 duty cycle.Here's a post employing a CMOS divide by 2 concept to produce a precise 50% duty cycle and amplitude waveform for an accurate squarewave reference.https://www.eevblog.com/forum/testgear/ac-rms-dmm-tests/Best,

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 01, 2024, 04:23:23 pm
content: I think you need the 7555, the CMOS version, for the alternative 50-50 output to work well, since the CMOS output can source and sink equally.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 04, 2024, 01:08:52 am
content: Quote from: PCB.Wiz on December 31, 2023, 11:12:57 pmSo I tried a decoupling Capacitor to pin 8 (Vcc). It didn't really make a difference.I also tried a series resistor on pin 3 (Out). I actually played with that in the beginning it also did not really make too much of a difference.I am not sure how to experiment with ferrite beads. Could you possibly elaborate on that.Thank you for your suggestion.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 04, 2024, 01:15:11 am
content: Quote from: CaptDon on January 01, 2024, 02:40:32 pmThank you for the suggestion. I am familiar with some of the difficulties of trying to achieve a 50-50 duty cycle with the 555. I'll have to try your suggestion as a learning exercise. At the current moment I don't think I have access to a CMOS divide by two follower.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 04, 2024, 01:18:15 am
content: Quote from: Andy Chee on January 01, 2024, 03:10:38 pmI'll give this a shot. Thank you for the suggestion. What is the thought process behind this circuit. Why is it better?When I posted this I was more concerned about the overshoot that can be seen in the attached pictures than I was about getting a 50-50 square wave.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 04, 2024, 01:27:29 am
content: Quote from: mawyatt on January 01, 2024, 03:31:56 pmI read your post. That's pretty neat that you came up with that. Have there been any changes to the design if I ever decided to make the PCB and build it?Like I mentioned before I wasn't striving for 50-50, that's not what this post was about. I was more interested in what's causing that overshoot and if there is a way to correct it.But I am also glad that people gave me suggestions on the 50-50 duty cycle as it gives me additional information and knowledge.Thank you.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 04, 2024, 01:36:49 am
content: Quote from: Alex Eisenhut on January 01, 2024, 04:23:23 pmThank you for the suggestion.Are not all 7555 the CMOS version?

author: Andy Chee
author_rank: Super Contributor
timestamp: January 04, 2024, 01:52:21 am
content: Quote from: JJ_023 on January 04, 2024, 01:27:29 amIn which case the first reply pretty much nails it, stray inductance.Apart from constructing on an etched PCB, you can prototype 'dead bug' style to keep leads short:

author: PCB.Wiz
author_rank: Super Contributor
timestamp: January 04, 2024, 01:58:03 am
content: Quote from: JJ_023 on January 04, 2024, 01:18:15 amOn an ideal part with rail to rail swings, and symmetric trigger points (1/3 and 2/3), R2 alone will give 50% duty cycle.A real (non CMOS) part does not quite manage rail to rail, so the added R1, skews the default 'almost 50%' to be closer to 50%.Quote from: JJ_023 on January 04, 2024, 01:18:15 amYou could also try pullups and pull down loads.The original 555 has a multiple transistor output drive, which unlike CMOS does not pull cleanly to VCC. This will not give a 'clean' rail to rail square wave.If you have any CMOS logic, you could try adding a non inverting buffer, and scope that.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: January 04, 2024, 02:13:36 am
content: Quote from: Alex Eisenhut on January 01, 2024, 04:23:23 pmNot quite.The CMOS parts have MOSFETS that can drive rail to rail, but the P & N FETS do not have equal resistance, so they cannotsource and sink equally.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 04, 2024, 02:28:22 am
content: Quote from: Andy Chee on January 04, 2024, 01:52:21 amThanks for that. What about a perf board?

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 04, 2024, 02:30:50 am
content: Quote from: PCB.Wiz on January 04, 2024, 01:58:03 amThank you for the suggestions and the explanation. I don't have any CMOS logic. I'm going to play with pull-up and pulldown loads, see what that does.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 04, 2024, 02:34:57 am
content: Quote from: PCB.Wiz on January 04, 2024, 02:13:36 amThank you for the clarification. I primarily stick to Texas Instruments for parts for stuff like this. In this particular case I used SE555 from a leftover project I had. I will have to get some LMC555 and try that.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 04, 2024, 02:41:16 am
content: Quote from: JJ_023 on January 04, 2024, 02:28:22 amYep perfboard is ok, but just like PCB track routing, be mindful of how you route the wires on your perfbord.Incidentally, some people use the terms perfboard, stripboard, and veroboard, interchangeably. However the way I distinguish between the two is that, perfboard only has solder pads, whereas stripboard/veroboard has parallel copper tracks.In the context of low parasitic inductances, go for the perfboard.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 04, 2024, 02:46:03 am
content: Quote from: Andy Chee on January 04, 2024, 02:41:16 amThank you for the concise explanation.Do you ever reuse your perfboards? I do.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 04, 2024, 03:08:22 am
content: Quote from: JJ_023 on January 04, 2024, 02:46:03 amI do, but often I’m impatient desoldering, delaminate a solder pad, and end up throwing the board out anyway!

author: PCB.Wiz
author_rank: Super Contributor
timestamp: January 04, 2024, 04:14:34 am
content: Another part to consider for 50% & 5V, is a 74HC4060, which guarantees 50% and can use smaller more stable capacitors to generate your 5kHz.HEF4060 can also work at 5V, with lower Icc, but has lower drive on the Qn outputs.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 04, 2024, 03:48:45 pm
content: Quote from: PCB.Wiz on January 04, 2024, 04:14:34 amThank you for the recommendation. I read the datasheet.https://assets.nexperia.com/documents/data-sheet/HEF4060B.pdfUnfortunately the datasheet was not Texas Instruments. The reason I say that and the reason I like to use Texas Instruments parts is they give a very detailed description of how it operates along with a whole bunch of circuits that I learn from, they also have links to white papers that educate on the subject matter. Never understood why all companies don't do that. I will have to do a little bit more research and figure out how to use this chip properly.Seems like a great chip. Fairly cheap, like $0.50.

author: Ian.M
author_rank: Super Contributor
timestamp: January 04, 2024, 04:03:43 pm
content: T.I do a 74HC4060 as well.https://www.ti.com/lit/ds/symlink/sn74hc4060.pdfDifferent manufacturer's 74HC parts are generally drop-in replacements for each other so if you find T.I. datasheets easier to understand, use them for everything except *exact* electrical min. and max. parameters, for which if you are pushing the limits, you should refer to the actual manufacturer's datasheet.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 04, 2024, 06:56:12 pm
content: Quote from: Ian.M on January 04, 2024, 04:03:43 pmThank you for pointing out those details. When I searched for that particular chip I didn't see one available under Digi. Unfortunately this particular TI datasheet is not the usual kind and doesn't have application notes. Would you happen to know of a schematic that would work in this particular case that I can analyze and learn from?

author: PCB.Wiz
author_rank: Super Contributor
timestamp: January 04, 2024, 07:10:09 pm
content: Quote from: JJ_023 on January 04, 2024, 03:48:45 pmYes, TI data is generally good for new parts, but for their ancient parts like CD4060 and SN74HC4060, they are often scans of old paper printouts.Quote from: JJ_023 on January 04, 2024, 06:56:12 pmThe Nexperia data on CMOS logic is probably the best - they have circuits, and equations and curves of typical operation.(eg their HEF4060 is tagged Rev. 10 — 8 November 2021)If you are learning, you could try the 15V and 5V CMOS parts and compare them. At your 5kHz and 5V, both will work.

author: tggzzz
author_rank: Super Contributor
timestamp: January 04, 2024, 07:42:24 pm
content: Quote from: CaptDon on December 31, 2023, 11:09:28 pmAlmost certainly true.Better breadboard techniques athttps://entertaininghacks.wordpress.com/2020/07/22/prototyping-circuits-easy-cheap-fast-reliable-techniques/

author: mawyatt
author_rank: Super Contributor
timestamp: January 04, 2024, 08:46:41 pm
content: Quote from: JJ_023 on January 04, 2024, 01:27:29 amYou can use various parts for this to work, and it does work extremely well as shown!!We used a CD4060 with a Crystal, Precision 5V reference, and a discrete CMOS Inverting Buffer. You can replace the discrete buffer with a standard CMOS buffer and parallel the outputs for a lower output impedance, any good 5V reference is also OK. Since one can measure the DC value of the 5V reference with a quality DMM, then the AC RMS value can be inferred with very good precision, follow discussion on the indicate thread for more details.Best,

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 05, 2024, 01:13:31 am
content: Quote from: tggzzz on January 04, 2024, 07:42:24 pmThanks for the link. It was an interesting read. I have worked with Perf board. But according to that article it's a lot less desirable than some of the other techniques. I seen the other techniques utilized by others. I have always sided away from them due to the convoluted mess they create. But since so many well-regarded engineers use them I will have to reconsider and give it a try.

author: tggzzz
author_rank: Super Contributor
timestamp: January 05, 2024, 10:46:00 am
content: Quote from: JJ_023 on January 05, 2024, 01:13:31 amGlad you liked it.I've seen too many beginners be disheartened by the subtle (and not so subtle) problems getting their designs working with solderless breadboards. Perfboards have fewer problems. All techniques (including PCBs) have some disadvantages.The key points are to understand the positive and negative characteristics or every technique, weigh those against what you are doing, and choose the appropriate combination of techniques for that specific job.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 05, 2024, 11:23:45 am
content: Quote from: JJ_023 on December 31, 2023, 10:38:14 pmBefore anything, have you calibrated the oscilloscope probes recently?If not, note that there is a small trimmer inside of the probe's handle. Set the probe switch on 10x, attach it to the calibration signal from the oscilloscope, and turn the small trimmer to get the most flat response, with minimal overshoots/undershoots. The procedure is usually described with pictures in the oscilloscope's user manual, or in the probe's user manual.To get 50% precisely, as already said before, the easiest way is to start from 10kHz and divide it by 2 with a flip-flop (FF), to make it 5kHz . That will get you a 50% duty factor with no adjustement needed. Otherwise, the adjustement for 50% can be tedious to achieve, and hard to maintain it over time, or over temperature/Vcc/etc. variations.Kind request, please avoid starting titles or conversations with the word "so". My first language is not English, but in general, the word "so" as a start is not a good sign.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 05, 2024, 02:48:05 pm
content: Quote from: tggzzz on January 05, 2024, 10:46:00 amI did enjoy it thank you. Do you have any specific tips for using a perf board? I try to keep everything close together and use solid wire to make the necessary connections. If I can which is often not the case I try not to cross any wires.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 05, 2024, 02:54:35 pm
content: Quote from: RoGeorge on January 05, 2024, 11:23:45 amThank you for the suggestion. Whenever I use any piece of test equipment I always do a very basic test. Since I primarily always operate on 10X, every time I turn on the scope I quickly hook up to the scopes reference to check. I learned this a long long time ago. It's a lot quicker to troubleshoot a piece of equipment that you use for troubleshooting before you start using it.

author: 2N3055
author_rank: Super Contributor
timestamp: January 05, 2024, 03:07:00 pm
content: Are you using scope probe with ground wire and crocodile clip, or you use spring ground right at the tip?

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 05, 2024, 06:15:38 pm
content: Quote from: 2N3055 on January 05, 2024, 03:07:00 pmThat's a good point. I was using a 3 inch alligator Crocodile clip.

author: 2N3055
author_rank: Super Contributor
timestamp: January 05, 2024, 06:46:54 pm
content: Quote from: JJ_023 on January 05, 2024, 06:15:38 pmThat alone can create that overshoot.Try with spring ground, or if you don't have one wind thicker copper wire around it and solder to ground.

author: tggzzz
author_rank: Super Contributor
timestamp: January 05, 2024, 07:25:51 pm
content: Quote from: JJ_023 on January 05, 2024, 02:48:05 pmNothing beyond that.I find Manhattan (in any of the variants shown) easier because there is less planning (=>faster) plus a solid groundplane (=> electrically better), and a sheet of copper clad can be large and is cheap and strong.Have fun!

author: eneuro
author_rank: Super Contributor
timestamp: January 05, 2024, 09:50:04 pm
content: Quote from: CaptDon on December 31, 2023, 11:09:28 pmThere is no point in analyzing projects run on a breadboard

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 06, 2024, 12:45:02 am
content: Quote from: Andy Chee on January 01, 2024, 03:10:38 pmI went to play with this particular circuit and just realized it doesn't have a discharge pin connection. How does this work?

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 06, 2024, 12:46:32 am
content: Quote from: 2N3055 on January 05, 2024, 06:46:54 pmThis is why I responded the way that I did. I should know better but just overlooked it. I actually have several of those spring grounds. Thank you.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: January 06, 2024, 12:48:51 am
content: Quote from: JJ_023 on January 06, 2024, 12:45:02 amit does not need one, the 555 behaves as an inverting Schmitt buffer. it does not quite manage rail-rail, so the added pullup allows you to skew to 50%

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 06, 2024, 01:53:54 am
content: Quote from: PCB.Wiz on January 06, 2024, 12:48:51 amI'm going to try that circuit thank you for the explanation.I continued playing with this circuit to try and see what would help with the oscillation. I tried all the suggestions from the posts. Changing over to a spring ground clip did not really do much in this particular case ( although I know it is a valid suggestion). What made the most difference was putting a 100 nF ceramic capacitor on Vcc to ground.My question is now that the oscillation is mostly removed are we approaching the limits of this particular chip in terms of how crisp of a leading edge we can get just based on the chip itself?Just as a data point the circuit was slightly different that's why the voltage ,frequency and duty cycle do not match the original post. I wanted to see if I could re-create the Oscillations using different parameters.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 06, 2024, 03:05:05 am
content: I made the other version that was suggested for the A-stable 555. The image is attached. It managed a 50% duty cycle. Thank you guys for the suggestion.I noticed that the output is not as clean and sharp even with a capacitor at Vcc. See the attached image.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 06, 2024, 03:51:16 am
content: Quote from: JJ_023 on January 06, 2024, 12:45:02 amWhen the 555 is triggered to discharge, normally it is pin 7 which turns on an internal open collector transistor and shorts the capacitor to ground. In the above alternative configuration, we use the totem output on pin 3 to short the capacitor to ground.However the feature of interest is the charging path, rather than the discharge path. In the standard astable configuration, the charging path is via a different resistor. In the above alternative configuration, the charging path is via the totem output high on pin 3 and the SAME resistor.Having the charge and discharge path via the SAME resistor is what makes it easier to get 50/50, because you no longer have to precisely make the the two resistors equal.Come to think of it, try omitting R1 100kohm resistor. I don't think it's required provided you're using the CMOS 7555 variant. And even if you have the regular TTL 555, try removing it anyway and see what it does to the output duty cycle.The output may certainly have more overshoot on the leading edges, this is to be expected due to the high current totem output doing the capacitor charging.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 06, 2024, 11:40:47 am
content: Quote from: JJ_023 on January 05, 2024, 02:54:35 pmTo be honest, I never do that. I touch the tip of the probe with the finger.About probe calibration. It doesn't need to be adjusted very often, unless really big variations in temperature or air humidity happened since last calibration. About temperature, any calibration has to be done after about half an hour or so of idle running, so the instrument got to a stable temperature/humidity regime. If you calibrate the probe right at startup, after an hour of running, the calibration might be off, particularly if you are in an are with high air humidity and potential condensation.Another thing, when calibrating, you have to connect both the tip and the Ground of the probe.In the pic you attached at the OP, there are 2 things:- a very short spike right after each signal edge - that is from the inductance of the GND alligator wire. In fact, by how tall that spike is, I suspect you are probing with only one wire (as in, another probe was used only to connect its GND alligator to the minus, then the displayed line in the picture is from a second probe with its alligator disconnected)- then, a long but small amplitude slope, for about half the width where the line was supposed to be flat - that might be from the probe calibration. Not a certitude, but might be.To eliminate the calibration hypothesis, please post a printscreen of the calibration signal, then a printscreen of the 555 signal. Both taken at about the same time, one after another, and what's most important, both taken by making use of the GND alligator, don't let it disconnected.A 3rd capture while using the spring connector at the tip of the probe, and by touching the GND and the out pins of the 555 directly with the spring attachment that came with the probes. Then a 4'th pic with the physical circuit on the breadboard, with the measuring probe(s) connected.I'm asking for all 4 pictures because I know you are careful to details, and particularly interested in getting the optimal. We can discuss the 4 pics later as a concrete example, in order to highlight more details about electronics in general, and probing in particular.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 07, 2024, 12:49:49 am
content: Quote from: Andy Chee on January 06, 2024, 03:51:16 amI appreciate the detailed explanation. It all makes sense. I tried your suggestion. You can see the results in the attached.My 1st question is why did you recommend 100 K ohm resistor in the 1st place if this works without it?The setup Is attached with the 100 K ohm resistor omitted. I tried different variations of R2. The images attached show the values for R2.The capacitors were 47nF.Here are the following observationsI was not able to achieve a 50% duty cycle with one resistor.The waveform does not seem as stable as the original.The 555 that I am using is the Texas Instruments SE555.https://www.ti.com/lit/ds/symlink/se555.pdf?ts=1704543624724I had a few of these around and I like this particular chip because unlike most 555 chips it will operate up to 18V. I don't think this is a CMOS variant maybe someone can correct me or affirm me.Again thank you.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 07, 2024, 02:02:22 am
content: Quote from: RoGeorge on January 06, 2024, 11:40:47 amThank you again for such a detailed response.You probably shouldn't touch the tip.I am familiar with the calibration process fairly well.You say the spike is at the end of the waveform I thought that was the beginning of the waveform. Which 1 of us is correct?Here are a few data points. The ground clip was always used. It was used alligator style from the probe that took the measurement. You can see the probe placement in the original breadboard set up in 1 of the attached pictures below.As you requested. The 1st picture and the 2nd picture are both of the probe calibration signal. The 3rd picture is the schematic that was utilized. The 4th picture is the original setup that was used. The 5th picture is the set up that was in response to this post.The 6th picture is utilizing the alligator clip. The goldplated pins on the breadboard is where the connection was made.The 7th picture is utilizing a spring ground. The connection was made directly from pin 1 to pin 3 by the probe.Looking forward to your comments as well as anybody else that wants to chime in. Tips and criticism welcomed.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 07, 2024, 03:56:20 am
content: Quote from: JJ_023 on January 07, 2024, 12:49:49 amWell when I first posted the circuit, I had no idea which 555 you were using!Your SE555 is indeed the TTL version, so using the 100k will help make the duty cycle closer to 50/50.If using the CMOS 7555 version, this resistor can be omitted because its pin 3 output will have a more balanced voltage swing compared to the TTL.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 07, 2024, 04:26:23 am
content: Quote from: Andy Chee on January 07, 2024, 03:56:20 amThanks for the response. I did a little bit more reading on the 7555. I found an interesting version which goes up to 2.5 megahertz. In their datasheet it talks about exactly that, being able to run a stable mode with one resistor.http://www.aldinc.com/pdf/ALD7555-7556.pdf

author: Andy Chee
author_rank: Super Contributor
timestamp: January 07, 2024, 05:05:03 am
content: And for a bit of a twist in 555 variants, here's one built with a (non-volatile) programable decade counter:https://www.customsiliconsolutions.com/downloads/Revised%20Standard%20products/CSS555_Spec_2.pdf(see page 2 for a block diagram)Coming from a 12C509 programming history, after all these years I'm still not exactly sure which niche the CSS555 fulfils.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: January 07, 2024, 08:42:27 pm
content: Quote from: JJ_023 on January 07, 2024, 04:26:23 amThat part is not cheap, but it does have impressive PSRR on the graphs. (tho not reflected in the tables ? )Quote from: Andy Chee on January 07, 2024, 05:05:03 amYes, the CSS555 is also not cheap. However, it does manage good precision with small caps and low uA. (typ 1% and 35 ppm/°C )MCU's alone struggle to match the Icc/precision levels, as most low power oscillators in MCU focus on power first, and dF/dT and dF/dV later.Many fail to even spec tempco and PSRR of their low power osc.The emergence of 20c MCUs has pushed the low power 555 into smaller niches.A MCU with a 32kHz crystal can still cost less than a CSS555, and the crystal leapfrogs into much better precision.Some MCUs allow you to calibrate the poor kHz osc against the better MHz osc, at some small code and icc cost.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 07, 2024, 08:43:33 pm
content: Quote from: Andy Chee on January 07, 2024, 05:05:03 amThank you for sharing that. I read the datasheet. The only niche that I could possibly see is in applications where you might need to modify the frequency by programming the onboard EEPROM. The other niche is that they claim to require the least amount of power, so maybe in certain battery longevity applications it would make sense as well.It's also rather expensive at almost $3.At 1/3 of the price you could get the Texas Instrument version (LMC555 CMOS Timer). Which in my opinion is superior in almost every manner.https://www.ti.com/lit/ds/symlink/lmc555.pdf

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 07, 2024, 08:45:42 pm
content: Quote from: PCB.Wiz on January 07, 2024, 08:42:27 pmThank you for your opinion. What do you think of the Texas Instrument version (LMC555 CMOS Timer)?https://www.ti.com/lit/ds/symlink/lmc555.pdf

author: PCB.Wiz
author_rank: Super Contributor
timestamp: January 07, 2024, 09:33:41 pm
content: Quote from: JJ_023 on January 07, 2024, 08:45:42 pmThat's a different point on the price/performance curve.LMC555 specs typ 100uA at 5V and 75 ppm/°C, so that's a distant second to CSS555 specs of 4.3µA at 5V and 35 ppm/°C.Of course, you need to decide how much you are prepared to pay for the better numbersFor other price curve info, look at lcsc which has CMOS 555 for sub 8c/500 - any of those could be 'good enough' for most use cases.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 07, 2024, 09:46:27 pm
content: Quote from: PCB.Wiz on January 07, 2024, 09:33:41 pmHow do those 2 compare at 12V?All kidding aside I do appreciate the different variations. If I needed whatever specs I would definitely be willing to pay for it. The reason I chose SE555 was they were fairly cheap when I got them and most importantly they have a higher voltage tolerance than most variants. Often times I use them in Monostable to debounce switches for a variety of applications. It's a really cheap way to get a crisp button press.I know they have specific purpose built chips for debounce, and they definitely work but they are sometimes a little too expensive in the grand scheme of things.Again thanks for all the additional info.

author: zapta
author_rank: Super Contributor
timestamp: January 08, 2024, 05:48:52 am
content: One way to achieve 50% with a 555 is to use it as a Schmidt trigger. Something along this diagram.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 08, 2024, 09:13:37 am
content: Quote from: JJ_023 on January 07, 2024, 02:02:22 amThe ringing spike is expected to appear after each edge in that signal (I didn't say at the end of the waveform). An edge can be either falling-edge or raising-edge.The forum is in maintenance, works intermittently, and the old forum bug about attachements seems to be back again etc., plus that this thread is moving too fast, and in many directions at the same time. I'm afraid I won't be able to keep my promise of going into details about the requested pics. Thank you for attaching them. The currently attached waveforms are much better than the ones in the OP.Looks good, keep experimenting!

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 08, 2024, 02:14:55 pm
content: Quote from: zapta on January 08, 2024, 05:48:52 amThank you for taking the time for the schematic. I believe I already did this based on someone else's suggestion with the results posted in reply number 45. I wasn't able to achieve a 50% duty cycle. It was explained to me that is most likely because my 555 variant is not a CMOS variant.In post number 4 you can see the schematic used. I use that particular schematic omitting the 100 K resistor. Unless I am mistaken the circuit is basically what you are suggesting.

author: JJ_023
author_rank: Frequent Contributor
timestamp: January 08, 2024, 02:17:26 pm
content: Quote from: RoGeorge on January 08, 2024, 09:13:37 amThank you for clarifying the ringing. That was an oversight on my part. When I was writing that post there were issues with the site being down. No worries about your promise I totally understand. Thanks to your contributions.