555 Is This Feasible? - Page 1
Forum section: electronics / beginners

author: @rt
author_rank: Super Contributor
timestamp: September 16, 2022, 03:05:25 am
content: Hi,I want an oscillator with a square waveform duty cycle 9 mins low (approx), and 500ms high (approx).It is important that the low duration doesn’t exceed 10 minutes, so 9 minutes is just a generous error margin.It appears the only difference between t1 and t2 in the diagram is achieved by R2.Is it feasible to expect the desired outcome with the same capacitor C1 responsible for both durations?It occurs to me that I could replace R2 with a very high value resistor to increase t2,but can I keep t1 very low at the same time? The capacitor can’t be so large that t1 blows out.

author: ledtester
author_rank: Super Contributor
timestamp: September 16, 2022, 03:45:43 am
content: In this circuit the charging of the cap is determined only by R1 and the discharging of the cap only by R2.If you set C1 to 100uF you can get a 9 minute off period with R2 set to:R2 = 9*60/.693/(100*10^-6) = 7.8 M ohms.and for 0.5 seconds:R1 = 0.5/.693/(100*10^-6) = 7.2K ohmsIf you have a 1000 uF capacitor you can divide R2 and R1 by a factor of 10, i.e. 780K ohms and 720R respectively.

author: james_s
author_rank: Super Contributor
timestamp: September 16, 2022, 06:03:41 am
content: 9 *minutes*? It may be possible, but I would not expect it to be very precise. It would be trivial to do this with something like a attiny12 microcontroller though.

author: RoGeorge
author_rank: Super Contributor
timestamp: September 16, 2022, 08:24:52 am
content: Minutes long timing might not be reliable with a 555, would drift with temperature/humidity, and if you need more than one timer, then you'll need to calibrate each one manually, which would be very time consuming considering you'll have to wait about 10 minutes for each pulse.A microcontroller would be better, and for very small ones it might cost about the same if not cheaper than a 555. Many microcontrollers have an internal calibrated clock which doesn't need any external RC or Quartz. Usually the error of the internal oscillator is less than 10%, guaranteed over all the range of temps and voltages, and that can be calibrated for less than 1% if needed (without having to wait 10 minutes to check the calibration results).

author: jpanhalt
author_rank: Super Contributor
timestamp: September 16, 2022, 09:38:54 am
content: You might consider the CMOS version ICM7555 for longer time constants or the CMOS programmable version CSS555C(http://www.customsiliconsolutions.com/downloads/Revised%20Standard%20products/CSS555C_Spec.pdf) for extremely long periods. The latter will also work for 9 minutes.

author: @rt
author_rank: Super Contributor
timestamp: September 16, 2022, 10:13:42 am
content: Hmm... well for everyone else... It’s 10 minutes max, but can be arbitrary.... as I said in OP, there’s a minute error margin built into that time.The 9 minutes could even be lower.500ms is minumum, but I have mitigated error already with slightly higher value resistor.Micro I could do easy, but is also a bit overkill... I know not on price, but on complexity.

author: @rt
author_rank: Super Contributor
timestamp: September 16, 2022, 10:50:38 am
content: Introspection.Nobody else would know that the autism here won’t accept a million transistors doing the job of an astable multivibrator. So I should actually thank everybody. ThanksNo micro in this case for a hobby project anyway. For a larger run for commercial purpose, the autism would allow cost to dictate method.The initial question really is about freq drift.. ie. someone else who has done something similar please sanity check that temp coefficient of discrete components won’t ruin it.Now that I have constructed physically, I’ll accept a shorter low time (t2) until I am sure the 10 minutes won’t elapse.

author: MikeK
author_rank: Super Contributor
timestamp: September 16, 2022, 11:59:51 am
content: Capacitors have a typical tolerance of 20%. That affects your timing precision, of course. If 10 minutes is a hard limit you're going to want better precision than 20%. Many microcontrollers have 1-2% internal oscillator accuracy.

author: Circlotron
author_rank: Super Contributor
timestamp: September 16, 2022, 12:07:22 pm
content: I've seen 555 circuits with a 100uF cap and several megs of charging resistor and sometimes the leakage of the cap would be such that it would only charge partway and never get to the timing threshold.

author: CaptDon
author_rank: Super Contributor
timestamp: September 16, 2022, 12:41:22 pm
content: The 1000uf / 780K / 720 answer should not be used as I think 1K was the minimum data sheet value for that resistor. The suggestion of using the CMOS version is even recommended by the 555 datasheet for longer time delays. You can get much longer time delays using the CMOS version while avoiding using high leakage unstable electrolytic capacitors. I believe the CMOS version of the 555 datasheet even says right in the bold print 'Delays from minutes to hours'.

author: MrAl
author_rank: Super Contributor
timestamp: September 16, 2022, 02:21:52 pm
content: Quote from: @rt on September 16, 2022, 03:05:25 amHello there,You should know right off the bat that this is not a good way to do it even if it does work. So get off the bat and on the ball and find another way to do it or one day you'll be stuck out in left field, and if i can think of any more baseball metaphors i'll get back here later :-)But really RC timing with larger caps is a little problematic both in initial set points and long term age factors. There are other ways.One way in particular that doesnt involve a micro controller is to use a timer like the 555 with reasonable cap and resistor values and a digital divider chip that divides the 555 frequency down to a much lower frequency. You can go pretty far with this idea because then the 555 will be operating normally and digital dividers are very very very repeatable in their divide ratios, and in fact may be flawless for the most part. This technique is actually used in very important applications where a change in timing could blow out very expensive equipment. In fact in those cases even an LM339 can be used as the base frequency oscillator with the dividers following.If you really MUST go with a 555, then perhaps you can try multiple 555's. If you have one 555 trigger the next 555 you get a longer delay time using lower value caps and more reasonable resistor values. If you use more than two 555's you can probably go pretty far with this but you have to have the room for the chips on the board. Dont know if you are into SMD or not but the 555's also come in a dual package type so you get two 555's on one chip, and two chips means you have four 555's to work with. In fact, i would bet there is a better solution using LM339 comparator chips with a little thought. I might give that some thought myself it may be interesting.I've done delays that go into the days and one i remember best is a special kind of battery charger that had to charge the cells once every 12 hours. The timing was around 11.75 hours off, then 15 minutes on. I just have to say it was pretty darn easy to do that using a very very cheap microcontroller chip at the time made by MicroChip. That takes a bit of learning to do if you never programmed a microcontroller before, but today there is no excuse because of products like the Arduino. The Arduino microcontroller is used by hobby folks all over the world and with good reason. There is a host of information on the web and sample programs that are so easy to change you'd wonder why you never used one before.With the Arduino IDE you dont have to deal with the chip itself directly, dont even have to know how to solder. You can get jumpers that you plug into the Ard board and run a program that came with the IDE. From there a minor mod to the program and you can get delays that probably last longer than the age of the universe (ha ha). Seriously though you can get hours, days, months, years, you name it. You just need a 5v supply or even a 9v DC wall wart.The cheapest ones are the Nano and they are small too. The entire board is something like 1 inch by 3 inches and all the parts are on board already. If you need an output transistor that's really all you need to add except for maybe a resistor or two. If you dont know how to mod the program im sure someone here would surely help you and it would not be much to change either, maybe a few lines of code which is very human readable too. This kind of solution should get you a sure home run.Ok no more baseball metaphors for now, good luck with it and if you can please come back and let us know how you made out with it, whichever way you decided to do it.

author: Terry Bites
author_rank: Super Contributor
timestamp: September 16, 2022, 03:29:36 pm
content: I bumped ito this few weeks back. No nasty diode temcpco issues.www.edn.com/add-one-resistor-to-give-bipolar-lm555-oscillator-a-5050-duty-cycle/

author: james_s
author_rank: Super Contributor
timestamp: September 16, 2022, 06:12:11 pm
content: I think a microcontroller will be cheaper, and I'm certain it will have a lower component count. This is an application where even one of those 3 cent Padauk micros would do just fine, although the cheapest mainstream micro you can find is going to be a lot easier to develop for. Digikey has the ATTINY10-TS8R for 47 cents each in singles, SOT23-6 package is smaller than a 555.

author: Zero999
author_rank: Super Contributor
timestamp: September 16, 2022, 06:33:19 pm
content: Quote from: @rt on September 16, 2022, 10:13:42 amWhat leads you to this conclusion? An 8 or 6 pin microcontroller, a decoupling capacitor and some code is much simpler, than a 555 circuit.

author: james_s
author_rank: Super Contributor
timestamp: September 16, 2022, 07:24:38 pm
content: Quote from: Zero999 on September 16, 2022, 06:33:19 pmProbably lower power consumption too, possibly dramatically lower. The micro could spend the vast majority of the time in deep sleep mode drawing a few microamps, it could potentially run for years from a coin cell.

author: Bud
author_rank: Super Contributor
timestamp: September 16, 2022, 09:17:54 pm
content: Quote from: Zero999 on September 16, 2022, 06:33:19 pmHow it is simpler if it requires writing code and a programmer to burn it in. The 555 does not need any of that.

author: james_s
author_rank: Super Contributor
timestamp: September 16, 2022, 10:27:23 pm
content: Quote from: Bud on September 16, 2022, 09:17:54 pmIt has less parts on the board, that's the definition of simpler. Device programmers are cheap and most people who are serious about electronics will already have one. Writing the code for a project like this is trivial, I could probably do it in 5 minutes and I'm not much of a programmer. The 555 needs a pile of external components, the capacitor alone will cost more than the entire circuit using a microcontroller. (MCU and decoupling cap)

author: Nusa
author_rank: Super Contributor
timestamp: September 16, 2022, 11:37:49 pm
content: Quote from: MikeK on September 16, 2022, 11:59:51 amAll the components have tolerance values, but that just represents factory binning. After you've received them and tested actual values to be acceptable, the tolerance marking loses meaning. All that's left is environmental drift and long-term aging.

author: Vincent
author_rank: Regular Contributor
timestamp: September 17, 2022, 12:15:18 am
content: This may be a completely stupid idea, but say OP decides not to the uC route, what about a 555 with a shorter clock cycle running a binary counter like a CD4040 or something? Timing components for the 555 could be higher precision and/or more stable ones.

author: jpanhalt
author_rank: Super Contributor
timestamp: September 17, 2022, 09:47:46 am
content: Post #5 refers to the CSS555 chip -- a 555 with built-in programmable counter.Here are links to CSS's application notes and to the specific note that applies to programming. It looks fairly simple, but then, if you need to write an MCU program to program a 555, why use a 555? I suspect a development board is or was available to do that for you. No idea of the cost.https://www.customsiliconsolutions.com/products-for-ASIC-solutions/standard-IC-products_no.aspxhttps://www.customsiliconsolutions.com/downloads/Revised%20Standard%20products/CSS555_App_Note1_Serial_Interface.pdf

author: MrAl
author_rank: Super Contributor
timestamp: September 17, 2022, 11:38:09 am
content: Quote from: Bud on September 16, 2022, 09:17:54 pmThe Arduino has code that is already written for pulses that would be very simple to modify. Anyone here could easily do that i think.

author: MrAl
author_rank: Super Contributor
timestamp: September 17, 2022, 11:40:27 am
content: Quote from: Vincent on September 17, 2022, 12:15:18 amNo it's not stupid at all, and in fact it was already mentioned in reply #10 in this thread.There are even counters that divide by a large number in the thousands so that brings the components down to the normal size and value. Perhaps one 555 timer chip and one counter chip would do it. You do have to reset the counter at the right time though with possibly a logic gate. Since there are two time settings it may be necessary to use two counters and some glue logic.

author: MarkF
author_rank: Super Contributor
timestamp: September 17, 2022, 12:24:20 pm
content: Quote from: jpanhalt on September 17, 2022, 09:47:46 amAm I correct that the serial clock to program the EEPROM is between 2 MHz and 5 MHz?Not very user friendly if you have to have a microcontroller to program it.It would be nice if you could program it from a standard serial port at normal baud rates (i.e. in the low KHz).There is a lot of talk of meeting the OPs tolerances...He says he'll accept anything between 500ms and 10min.Just how hard can it be to meet a tolerance range like that?Quote from: @rt on September 16, 2022, 10:13:42 am

author: ledtester
author_rank: Super Contributor
timestamp: September 17, 2022, 12:57:30 pm
content: Quote from: MarkF on September 17, 2022, 12:24:20 pmHere is the app note on programming the chip:https://www.customsiliconsolutions.com/downloads/Revised%20Standard%20products/CSS555_App_Note1_Serial_Interface.pdfLooks like just a standard serial EEPROM. There's no mention of a maximum clock period. The minimum and typical durations are 500ns and 200ns respectively which corresponds to 2MHz and 5MHz but that's an upper bound on the clock speed.

author: magic
author_rank: Super Contributor
timestamp: September 17, 2022, 04:34:02 pm
content: CD4060? It's like 555 but with built-in frequency divider. It would probably need to trigger an ordinary 555 (or some discrete contraption) for the 500ms thing.I have seen those buggers used for multi-hour timeout in dumb NiCd chargers.

author: Terry Bites
author_rank: Super Contributor
timestamp: September 17, 2022, 04:37:10 pm
content: Do I need to quote Bob Widlar again?

author: floobydust
author_rank: Super Contributor
timestamp: September 17, 2022, 07:01:40 pm
content: 555 it's got digital, a flip-flop insideLong duration timing like OP's 9 minutes is never reliably done in the analog domain. Because you require a large value 470-1,000uF electrolytic capacitor with tiny charging current in the uA. The cap's leakage current dominates and is a temperamental beast, you'll spend a lot of your life testing the time delay, if it works.I'm not saying it can't be done, there's hundreds of bonehead 555 timer circuits with 10 minute delays out there. Build a few see how they perform or don't perform.If you had an hour to come up with something, a counter does it better whether CD4060 or an Arduino.

author: EPAIII
author_rank: Super Contributor
timestamp: September 20, 2022, 09:29:31 am
content: I may get dumped on, but there is no reason why a CMOS timer can not deliver a 9 minute cycle.https://electronicsarea.com/5-to-30-minute-timer-circuit-using-7555-ic/You do need to use a low leakage/low ESR capacitor because it needs to hold a charge for longer than that 9 minutes.With the original 555 I consider anything over one minute to be a stretch.Of course, a PIC would probably be both less expensive and more accurate. But some time would be spent programming it.

author: MrAl
author_rank: Super Contributor
timestamp: September 20, 2022, 12:25:42 pm
content: Quote from: EPAIII on September 20, 2022, 09:29:31 amUsing an Arduino you could probably mod the code in about 15 to 30 minutes depending on experience, or ask someone else to do it for you and they could do it quickly i believe.If the person never used an Arduino before, they would have to learn a little about using the IDE and the commands, but there are not many commands and once they learned it they could go on to use Arduinos for many other projects.I dont think anyone here is saying that you can not do 9 minutes with the right 555 version, the question is how accurate will it be and how much will it age over time. It would be hard to predict this i think, so it makes sense to try to find a more conventional way. I dont know how important the timing is in this project case though.Just some thoughts.

author: taste_tester
author_rank: Regular Contributor
timestamp: September 21, 2022, 09:22:33 am
content: A couple days learning how to do some insanely simple single function, albeit with weird timing, on a budget microcontroller vs making something analog and worrying that it stops working reliably for months or years?

author: EPAIII
author_rank: Super Contributor
timestamp: September 21, 2022, 10:34:56 am
content: The 555 is at least 50 years old and still available. From multiple sources when I last checked.How old is the oldest single chip microcontroller?Quote from: taste_tester on September 21, 2022, 09:22:33 am

author: MrAl
author_rank: Super Contributor
timestamp: September 21, 2022, 03:21:19 pm
content: Quote from: EPAIII on September 21, 2022, 10:34:56 amHi,Not sure what is your point here. Is it that 555's are more reliable because they have been around so long, or is it that they are so old that there must be something around that is better now.I think both 555's and uC's are useful in their own way for applications that could benefit from either choice.Also have to figure in the learning curve for using a uC is just one time, then you can program a million uC chips :-)I know people who dont know much about electronics but have used an Arduino within the first day they downloaded the IDE. That's because there are so many example programs you can start with. Granted they wont be able to program code for an aircraft flight controller, but they can do the simpler ones and gradually learn more and more.

author: taste_tester
author_rank: Regular Contributor
timestamp: September 21, 2022, 06:52:57 pm
content: Quote from: EPAIII on September 21, 2022, 10:34:56 amDude, who cares? Honestly. Also explain how it matters even an iota what the age of the component used isWe already established in this thread that the proposed circuit relies on extremely tight component tolerances, which would force the OP to buy some VERY expensive and fancy passive components of a very high grade, all for what, one duty cycle with an incredible acceptable range of 500ms to 9min? Just program the 3 cent micro to make a lousy pulse every 6 minutes and you're golden.

author: ledtester
author_rank: Super Contributor
timestamp: September 21, 2022, 09:25:40 pm
content: For a no programming solution this module looks interesting.. about 30 cents per unit shipped:Duration supposedly can be set between 2s and 1000 hours. Draws about 100uA when timing, 1uA when sleeping.https://www.aliexpress.com/item/3256803531968230.htmlReview:https://westsideelectronics.com/delay-timer-ic/

author: james_s
author_rank: Super Contributor
timestamp: September 21, 2022, 10:22:38 pm
content: Quote from: EPAIII on September 21, 2022, 10:34:56 amI fail to see your point. The 555 is a great part, I keep them in my parts stock, it has many uses, creating minutes long delays is not really a proper use of that part. The fact that a tool has been around for decades and is still useful doesn't mean it's the best or right tool to use for every task.

author: Nusa
author_rank: Super Contributor
timestamp: September 21, 2022, 10:23:03 pm
content: Quote from: EPAIII on September 21, 2022, 10:34:56 amA few years older than the 555, if you actually want the answer. If we limit to stuff we can still buy modern versions of, then a few years less. 6800, 6502, Z80 all came out around 1974-5.But the real story is the PRICE of a microcontroller vs the 555. The 555 launched at $0.75 in 1972, which was 2-3 orders of magnitude cheaper than processors at the time. Yes, processor prices came way down around 1975 when the 6502 was launched for a mere $25. Fast forward to today when it's common to find processors (the $0.03 processor made news a few years back) that are cheaper than 555 timers (about $0.16 per). (Don't forget inflation. Multiply 1975 prices by at least 5 to get modern buying power. Hobby electronics as a whole has gotten a LOT cheaper over the years.) Price is everything when it comes to new products....but for hobbyists and old designs, the 555 still has a place.

author: james_s
author_rank: Super Contributor
timestamp: September 21, 2022, 10:28:08 pm
content: Quote from: Nusa on September 21, 2022, 10:23:03 pmThe 6800, 6502 and Z80 are all microprocessors, not microcontrollers. There is a very significant difference, a microprocessor is a general purpose device that requires RAM, ROM, IO, address decoding, etc to function while a microcontroller is designed specifically to control hardware and has almost everything built in. I don't know off hand when the first microcontroller came out, the TMS1000 is the earliest one I know of off hand.

author: Nusa
author_rank: Super Contributor
timestamp: September 22, 2022, 01:45:46 am
content: Quote from: james_s on September 21, 2022, 10:28:08 pmThe answer is the same, although I admit lumping things together after that. The word microprocessor wasn't in common use at the time, so it's like the current situation with gigabyte vs gibibyte -- I know what you mean with either word if the context is there (and I still use the old words out of habit -- if I'm not understood, the person I'm talking to doesn't know the subject). TMS1802 happened in 1971 (became the 100 series, not 1000), and was used in Sinclair calculators in 1972. Even had segment drivers for the display. If you want something that's still around, I'd guess the 8051 launched in 1981 off the top of my head.My main point remains...it's the PRICE that makes these attractive as general purpose solutions vs the 555, not how old the design is.

author: Infraviolet
author_rank: Super Contributor
timestamp: September 22, 2022, 02:09:41 am
content: I'm fairly sure arduino supports ATTiny chips nowadays. And they appear to be programmable from a second arduino board (Arduino as ISP principles probably involving the avrdude command line tool in the background),https://create.arduino.cc/projecthub/arjun/programming-attiny85-with-arduino-uno-afb829.There is though erhaps one possible advantage of the 555 nobody has yet debated, availability and multiple manufacturers. Whilst there are ATTiny chips of the type wanted perhaps available right now, the next time a country somewhere starts a war, overreacts to a virus, speculates on a market, makes or breaks a trade deal, or the next time a factory burns down or a ship gets stuck in the suez or... then the specfic ATTiny you want and which you planned your design and PCB around might no longer be available. 555's being an old design, produced by multiple sellers, are a more generic device and so would be less vulnerable to production and supply chain disruption, probably, perhaps.I, for one, certainly find the idea of trying to do things using just generic parts to be an interesting challenge, though it definitely wouldn't be an ideal solution if logistics weren't so just-in-time-y and unreliable. If you want to avoid microcontrollers I'd think looking to something built up from multiple generic chips, perhaps 555's and some sort of counters, might be somewhere to go from.

author: Nusa
author_rank: Super Contributor
timestamp: September 22, 2022, 02:27:34 am
content: Quote from: Infraviolet on September 22, 2022, 02:09:41 amThere's another fun word: Arduino. You used it several times in your paragraph, each time with a different meaning!The 555 was never patented, so anyone can manufacture it. Everyone stole from everyoneat the time, patents or not, with a tacit understanding that this was good for the industry. At least for the small stuff. Signetics wasn't big enough to buck the system of the day, so they didn't bother. And they were acquired a few years later, so ceased to exist.

author: rdl
author_rank: Super Contributor
timestamp: September 22, 2022, 10:22:35 am
content: You know, some people just aren't that interested in programming or microcontrollers. They'd rather do things the hard way or the "old school" way. Maybe just for the challenge. I know, I'm a bit like that myself. I'm not saying it's the case here, just something to keep in mind.

author: floobydust
author_rank: Super Contributor
timestamp: September 22, 2022, 04:56:51 pm
content: It depends on how accurate you want the 9 minute and 0.5sec timing to be. Is 8-12 minutes ok for example.You can try a CMOS 555 timer with huge capacitor as you originally posted, but as I mention the cap's leakage current steals a big part of the charging current, and is not consistent with temperature, aging etc. so the delay time moves around, and it wastes a lot of your time with a stopwatch... waiting...Better way is a higher frequency clock with a divider IC to get down to the long delay time. Would you consider using aCD4060or CD4040 or CD4017 etc. counter IC that is fed a faster clock?Otherwise just build the 555 circuit and have some fun learning about it.

author: @rt
author_rank: Super Contributor
timestamp: September 25, 2022, 12:53:20 pm
content: It would take next to no time for me to achieve this with several types of microcontrollers.