200 Minute Timer Circuit Design Help – 8A 120VAC Load. - Page 1
Forum section: electronics / projects

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 13, 2024, 04:25:03 pm
content: I am asking the communities help in designing a circuit with the following parameters.Timer needs to be fine-tuned once and then left as is.The timer is going to be roughly 200 minutes.The circuit is going to switch an 8 A load at 120VAC 60 Hz. (In this particular case the load is primarily a heating element.) with a momentary LED switch. The switch initiates the timer as well as abruptly ending the timer sequence should that be necessary.I have built plenty of these types of circuits in the past. They all pretty much start out the same.I take a 120V AC to 12V DC power supply and use that for the momentary switch as well as for the timer circuit. The momentary switch is a lighted LED switch. The timer circuit is usually some sort of microcontroller. I have even used off-the-shelf products that are compatible with home assistant to get the ability to control the device from anywhere as well as giving Wi-Fi accessibility to the device.The timer circuit then drives the SSR (solid-state relay) to switch the load on and off. The SSR is typically rated to 100A AC and is controlled by 3-32V DC at 20mA (typically).The load also incorporates a fast blow fuse in its own dedicated fuse holder wired on the hot side.I am primarily looking for advice on how to implement the timer part of the circuit, maybe other variants. However, any overall ideas are also greatly appreciated in terms of improving what I am currently doing.Based on my previous posts on here on the 555 it was suggested to get a CMOS variant. I now have those in stock primarily the LMC555 CMOS Timer from Texas Instruments.https://www.ti.com/lit/ds/symlink/lmc555.pdf?ts=1715555308343Is it worth creating a timer circuit out of this chip (Monostable mode)? The resistor values are in the 1G ohm range with a 100uf capacitor, or is it better to just stick with a microcontroller?Is there a better solution than those two for a timer to accomplish what I am looking to do?As always thank you to everyone in advance that participates

author: themadhippy
author_rank: Super Contributor
timestamp: May 13, 2024, 05:17:14 pm
content: binary counter and a few and gates?

author: PCB.Wiz
author_rank: Super Contributor
timestamp: May 13, 2024, 05:55:49 pm
content: Timer parts like HEF4541, HEF4521, and even 4060 x 2 avoid very large values and make testing easy.You could also look athttps://www.eevblog.com/forum/projects/how-to-shorten-the-signal-to-my-doorbell/msg5467111/#msg5467111Where a timer-relay was the best (simplest,quickest,least wiring) solution.

author: xvr
author_rank: Frequent Contributor
timestamp: May 13, 2024, 06:04:04 pm
content: QuoteQuoteWhy not microcontroller? You can use some tiny MCU with 8 pins, it will be even simpler than 555 timer and post dividers.

author: Gyro
author_rank: Super Contributor
timestamp: May 13, 2024, 06:33:35 pm
content: It depends on the OP's skill set,either method is valid. The technique they intend to use to determine and adjust the required time may also be relevant.Edit: Scrub that, he has used microcontrollers before. Also, trying to use a monostable with such high resistance and capacitance values will be far too sensitive to board leakages, contamination, atmospheric humidity even. I'd consider that a non-starter.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 13, 2024, 06:39:16 pm
content: Quote from: themadhippy on May 13, 2024, 05:17:14 pmI am familiar with both of those components and the proposed solution although I have never done it. However I am unaware of how to implement it. I will have to look into it.What would be the advantage of this over a microcontroller or a cmos 555?

author: Gyro
author_rank: Super Contributor
timestamp: May 13, 2024, 06:43:25 pm
content: Sorry, I was just posting an edit to my above post when I saw yours. As I explained, there's no way you'll be able to do it in a single CMOS 555. You need to start with a faster clock and divide it down to stand any chance over 200 minutes.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 13, 2024, 06:49:12 pm
content: Quote from: PCB.Wiz on May 13, 2024, 05:55:49 pmI have read the data sheet for the HEF4541 it would definitely work and it is similar to the first responders post just an all-in-one solution.I read that post they had some interesting suggestions. Thank you for sharing all that information.

author: xvr
author_rank: Frequent Contributor
timestamp: May 13, 2024, 06:50:40 pm
content: Quote from: JJ_023 on May 13, 2024, 06:39:16 pmThere is impossible to beat MC over everything. 1 IC without any external circuitry (except blocking capacitor) - there is impossible to do any smaller/better.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 13, 2024, 06:51:54 pm
content: A microcontroller is what I currently use as I stated in the opening post. An Arduino would work as well. I was just looking to expand my knowledge and see if anything could be improved upon or be made aware of something I was not. Thank you.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 13, 2024, 06:55:10 pm
content: Quote from: Gyro on May 13, 2024, 06:33:35 pmThat was my concern with the monostable approach. Thanks for pointing out and confirming this. What do you think would be a good solution for a long timer besides microcontroller (that's what I am currently using)? Definition of long timer being three hours.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 13, 2024, 06:58:02 pm
content: Quote from: Gyro on May 13, 2024, 06:43:25 pmThank you for elaborating on this. I had reservations about the time length that's why I wrote this post. I wanted to see if there is another solution besides a micro controller. Don't get me wrong I have no issues with using a microcontroller. I've done dozens and dozens of projects with them. I just want to see if there is another solution to expand my knowledge and maybe broaden my exposure to things that are out there that I had no clue exist.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 13, 2024, 07:01:28 pm
content: Quote from: xvr on May 13, 2024, 06:50:40 pmThat was my thought process as well. Also for people that might be reading this in the future that are not comfortable with microprocessors I would recommend looking at some of the home automation modules which interface with home assistant.You don't really need any programming skills to be able to get them to function in this intended manner.

author: Gyro
author_rank: Super Contributor
timestamp: May 13, 2024, 07:03:45 pm
content: Quote from: JJ_023 on May 13, 2024, 06:58:02 pmAs PCB.Wiz points out, using a 74HC4060 (or two) even a CD4060, will give you a 14 stage binary divider (1/16384), a simple cmos gate oscillator and a clear input, all in one chip. Your RC time constants then become a lot more sensible. I've used them before for very basic battery charger timers. The datasheet should give you all you need.

author: themadhippy
author_rank: Super Contributor
timestamp: May 13, 2024, 07:13:05 pm
content: Quoteclock a binary counter once a second (the above mentioned cd4060, a 32.7khz crystal and a dived by 2 circuit for example) and combine the counter outputs with AND gates so when the count reaches 10111011100000 it stops

author: mariush
author_rank: Super Contributor
timestamp: May 13, 2024, 07:13:12 pm
content: Easier than a microcontroller? Probably a small motor and a bunch of reduction gears that would cause a wheel to make a half rotation or full rotation in 200 minutes.basically a simplified version of thisOr... thinking cassette tapes ... have a cassette tape run at slow speed so that the tape ends at exactly 200 minutes... you can detect tape end with an optical sensor (tape becomes transparent at the end)

author: Gyro
author_rank: Super Contributor
timestamp: May 13, 2024, 07:18:47 pm
content: Quote from: mariush on May 13, 2024, 07:13:12 pmI sense a competition coming on.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 13, 2024, 07:59:08 pm
content: Quote from: Gyro on May 13, 2024, 07:03:45 pmThank you for that. I looked at the data sheet for the Texas Instruments. Maybe I will order one and play around with it.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 13, 2024, 08:00:30 pm
content: Quote from: themadhippy on May 13, 2024, 07:13:05 pmI get the gist of this but do not fully understand how to do this. I'll try to look into it. Thank you.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 13, 2024, 08:01:44 pm
content: Quote from: mariush on May 13, 2024, 07:13:12 pmThat is a great post apocalyptic design.Thank you for the ingenuity.

author: Zero999
author_rank: Super Contributor
timestamp: May 13, 2024, 08:06:40 pm
content: Quote from: JJ_023 on May 13, 2024, 06:51:54 pmYou can use the smallest, simplest, 6-pin microcontroller you can find and program it in assembly, rather than C.

author: mag_therm
author_rank: Frequent Contributor
timestamp: May 13, 2024, 08:36:37 pm
content: I am working on a separate "hardware" watchdog timer to stop ham sdr radio transmitter in event of cpu hang.The timer I selected is "DC 12V FRM01 Timer" one of the generic modules available on Amazon, $17 for (2).It has 18 modes, 0.1 s to 270 h and a 14 page programming manual that can be downloaded separately.The c/o contact is rated 125V AC 10 Amp, but recommended rating is 1/2 for resistive or 1/3 for inductive/capacitive.The AC contacts look well sized, separate from circuit and surrounded by ground planeThe modes are programmed with onboard buttons and led numeric display. There is a terminal for 1 20 ms pull up/pulse contact.This timer comes in versions for 5V, 12V and 24VDC supply, and there are a number of similar ones to this part number.

author: ledtester
author_rank: Super Contributor
timestamp: May 13, 2024, 09:12:18 pm
content: Quote from: Gyro on May 13, 2024, 06:33:35 pmMight check out the "C005" timer COB module which can produce delays from "5 seconds to over 40 days."https://westsideelectronics.com/delay-timer-ic/

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 13, 2024, 09:17:33 pm
content: Quote from: Gyro on May 13, 2024, 07:18:47 pmHow about a narrow throated funnel, filled with fine sand, which drops on a plate below which is attached to a strain gage?Now seriously , the CD4541 or other similar long range counter is actually your best bet, as previously suggested.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: May 14, 2024, 01:08:51 am
content: Quote from: JJ_023 on May 13, 2024, 04:25:03 pmQuestions here are how much fine-tune and for what values of 'roughly' ?Digital dividers are very simple, and you can get very accurate binary multiples, from any frequency. (mains, or 32.768kHz)With a programmable divider, like a 40103, you can get finer digital controlRC oscillators are easy to adjust, with a trimpot or fixed resistors, and should be stable to 1%~ 0.1% from setpoint.A small MCU would need to have some ADC ability, to allow for the adjust side.If it is done using Logic, or a MCU, some test pin that is meter-able quickly, can let you know what the setting is, without waiting 200 minutesSome of those logic parts have a fast-test pin so a MCU design could do similar.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: May 14, 2024, 02:14:03 am
content: Quote from: JJ_023 on May 13, 2024, 07:59:08 pmAnother part well matched to your problem is the 74HC5555. Now EOL but some still available.That is a 2^24 divider + monostable, so needs 1398.1013Hz for 200 minutes pulse, when /2^24It has 4 divider choice pins, so you can pick faster test times. eg a 2^17 choice would give 93.75s test times, for 200 minute setting.Or, on a pre-built MCU side, AliExpress have LCD versions of the venerable relay-timershttps://www.aliexpress.com/item/1005001800364875.htmlThe LCD ones seem to all use Nuvoton N76E003, which is a 16K 1T 8051 core.Addit : here is a relay timer based on the CD4541https://www.aliexpress.com/item/1005006185622775.html?

author: Uunoctium
author_rank: Frequent Contributor
timestamp: May 14, 2024, 02:40:52 am
content: I prefer using Omron timing relaysH3CR-A8 dial wheel, 1,2s-300h: starting at $9,50H3CA-A 306 LCD, pushbutton preset, 99,9s-9999h: starting at $25! both versions need the matching base/socket !above prices are for bay items from Hong-Kong labelled ‚made in PRC‘, so i can't guarantee, if they are not fake(I own many from the U.S.A. and they have worked accurately for years)

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 14, 2024, 02:48:06 pm
content: Quote from: Zero999 on May 13, 2024, 08:06:40 pmThat is a great suggestion. I can code in C not assembly. Thank you.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 14, 2024, 02:51:12 pm
content: Quote from: mag_therm on May 13, 2024, 08:36:37 pmI am familiar with those particular timers. I usually avoid them because it's just the board and then you have to figure out some sort of enclosure. When I use off-the-shelf components like that I actually look to the home automation space. Those devices are super simple to configure as a timer and enable you remote access to the device both to monitor and control.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 14, 2024, 04:07:00 pm
content: Quote from: ledtester on May 13, 2024, 09:12:18 pmThank you so much. That C005 chip is pretty neat. I read a few articles on it as well as the TPL5111 and variant from Texas instrument.The problem with the C005 that I see with this application is from the following."The chip is not repeatedly triggered, meaning that in the time between it is triggered and resets, it will not respond or keep track of any other falling signals from the external controller."https://westsideelectronics.com/delay-timer-ic/https://www.ti.com/lit/ds/symlink/tpl5111.pdf?ts=1715637205537https://www.ti.com/lit/ds/symlink/tpl5110.pdf?ts=1715617409200So this would prevent the user from stopping the cycle if that need arose. Unless I am misinterpreting something.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 14, 2024, 04:09:57 pm
content: Quote from: schmitt trigger on May 13, 2024, 09:17:33 pmI will have to look into how to implement that particular chip. Thank you for the suggestion.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 14, 2024, 04:17:22 pm
content: Quote from: PCB.Wiz on May 14, 2024, 01:08:51 amThank you so much for the suggestions.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 14, 2024, 04:24:10 pm
content: Quote from: PCB.Wiz on May 14, 2024, 02:14:03 amThose timers that you are showing I am very familiar with. I prefer not to use them. In a previous post I stated that I think there are better options available in the home automation section that not only enable you to control the device but to monitor it remotely. They also come in finished cases and are very small and compact in nature. Most of these types of home automation devices are actually rated for 10 A. I however never connect them directly without something in the middle like a SSR.Thank you for the suggestion on 74HC4060. I tried to look it up but almost every place is out of stock. I try to avoid EOL chips.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 14, 2024, 04:27:02 pm
content: Quote from: Uunoctium on May 14, 2024, 02:40:52 amThose I think would definitely work. I prefer my current solution that I described in the opening post. But thank you for a great suggestion.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: May 14, 2024, 07:56:23 pm
content: Quote from: JJ_023 on May 14, 2024, 04:24:10 pmThe 4060 should be very much alive from multiple sources.You may have meant the 74hc5555, which is single sourced, and now EOL? (Tho Rochester show ~500,000)The 74hc5555 has good data, and is operationally very close to what you ask for.QuoteThe stop on same button feature is rare, so you would need to do that in separate hardware.Most common would be a simple RC from the trigger button to reset, so a long press would stop.If you want a true toggle button, you would use a D-FF with Schmitt clock, and probably a RC POR reset and the timer reset.TI have a new family of 74HCSxx parts, that document Schmitt on every pin.Nexperia 74LVC parts also mention Schmitt pins.Release of new logic families shows MCU’s have not entirely replaced logic.

author: temperance
author_rank: Super Contributor
timestamp: May 14, 2024, 11:20:24 pm
content: Run's on two lemons.Adjustable Wake-Up Period: 250ms to 39 Dayshttps://www.analog.com/media/en/technical-documentation/data-sheets/2956fa.pdf

author: PCB.Wiz
author_rank: Super Contributor
timestamp: May 14, 2024, 11:41:24 pm
content: Quote from: temperance on May 14, 2024, 11:20:24 pmThat looks to be a pulsed-wakeup design timer ? (period = time between pulses?)There are a few niche parts like that, tho I'm not sure who buys them in volume, in 2024, at those premium prices ?Analog Devices LTC2956IM 1 $6.9000 10 $6.2320 1000 $2.8700Maybe those who really need the edge features, like 36V max, or sub 1uA timing, or small size ?It could allow designers using bigger MCU/MPU to focus on features other than deep sleep.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 15, 2024, 12:18:06 am
content: Divider off the mains frequency perhaps - more accurate than RC. 200 mins = 12000 secs. CD4020 & a couple of diodes to stop when bits 12 and 13 go high ( 12,288)

author: temperance
author_rank: Super Contributor
timestamp: May 15, 2024, 03:34:24 am
content: QuoteI have no idea who might be using those. But there must be a market for them because TI has something similar.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 17, 2024, 12:25:09 am
content: Quote from: PCB.Wiz on May 14, 2024, 07:56:23 pmI probably made a mistake and looked at the wrong chip. I just looked at the chip again and see that a bunch of it is in stock. Thank you for pointing that out.All the suggestions that you make as well as other community members really open up the possibilities for me and expand my knowledge as to what is out there. For that I am truly grateful.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 17, 2024, 12:26:15 am
content: Quote from: temperance on May 14, 2024, 11:20:24 pmDefinitely a neat little chip thank you.

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 17, 2024, 12:39:37 am
content: Quote from: mikeselectricstuff on May 15, 2024, 12:18:06 amKeep in mind I am still somewhat of a beginner. The way I understand what you wrote is that you would use the 60 Hz mains as a clock that you would then use a counter to keep track of time. When it reached 12000 it would stop. This is a great solution for this part of the equation.Is this correct?The part I don't get is how do you use a couple of diodes to stop. I don't have any real experience with counters or dividers.Thank you in advance.

author: themadhippy
author_rank: Super Contributor
timestamp: May 17, 2024, 01:24:37 am
content: Quotehave a look athttps://tinyurl.com/23jvjxtjthe top counter just keep counting from 0 to 15 ,the bottom one gets to 9 (q0 and q3 high),on the next clock pulse outputs q1 and q3 are the next to go high,causing the and output to go high which resets the counter back to 0

author: exmadscientist
author_rank: Frequent Contributor
timestamp: May 17, 2024, 02:09:38 am
content: Quote from: temperance on May 15, 2024, 03:34:24 amThe people who buy them are the people who don't want their critical functionality (watchdogs, life-critical timing, etc) done in software. Basically people who don't want software supervising software. Or people who have no programmed parts on a board and don't want to add a programming step just for that one little function. (This used to be more common, but most designs now have some kind of programmed part, and it's gotten much cheaper to do either way.)The6995is also probably an option here but would need some glue gates to muck with RST.I love these little guys and would buy tons of them if they were priced sanely. Alas, they're not. So no sales.

author: Smokey
author_rank: Super Contributor
timestamp: May 17, 2024, 02:27:04 am
content: Quote from: schmitt trigger on May 13, 2024, 09:17:33 pmEven better would be if the strain gauge was being measured by a microcontroller that had an ADC timer set to take a reading every 200 minutes...

author: PCB.Wiz
author_rank: Super Contributor
timestamp: May 17, 2024, 03:08:14 am
content: Quote from: JJ_023 on May 17, 2024, 12:39:37 amYou can get close, but you do need a bit more than a single 4020 divider.If you have 60Hz mains, that's /720000, and most long counters are binary.Thus log2(720000) is 19.45763738 binary bitsThe closest binary taps for your target of 200 are2^19/60/60 = 145.635 minutes2^20/60/60 = 291.271 minutesIf we assume you have outputs available on all binary counters, you can wait a bit longer, for more than one output to be HIGH.thus(2^19+2^17+2^16)/60/60 = 200.248 minutes - ie an AND gate combining counter taps at 19,17,16 will first pulse high at 200.48 minutes.You wanted some adjustment, so you could for example pick taps at 19 and 17..14 for 16 choices (4 switches or jumpers), next longest is 204.8 mins or a ~2.2% step size.More taps give finer digital settings, eg 5 taps/switches or jumpers is ~ 1.1% step size.Or, if you like analog, you can use weighted resistors and a RRIO comparator and trim pot, to 'pick a step'.

author: quadtech
author_rank: Regular Contributor
timestamp: May 18, 2024, 10:17:50 am
content: Quote from: mikeselectricstuff on May 15, 2024, 12:18:06 amHere is an example for this -https://www.electroniq.net/other-projects/power-supply-connection-delay-circuit.htmlThe timing chart is based on 50Hz. For 60Hz, the timing increments will be in 4.25 seconds instead of 5.1

author: soldar
author_rank: Super Contributor
timestamp: May 18, 2024, 10:48:02 am
content: https://www.ebay.com/itm/176152872783

author: Gyro
author_rank: Super Contributor
timestamp: May 18, 2024, 12:01:55 pm
content: Quote from: quadtech on May 18, 2024, 10:17:50 amNote that Elektor (the original diagram source) were sometimes not very careful with their mains circuit schematics. The whole circuit is at mains potential, so should not be grounded or connected to the case (which needs to be double insulated, or grounded if metal). See attached...EDIT: Input mains ground should also be carried through to the load of course.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: May 18, 2024, 12:28:19 pm
content: Good Morning JJ, yet another ready-made option:http://www.paragoncontrol.com/timer.html

author: JJ_023
author_rank: Frequent Contributor
timestamp: May 25, 2024, 01:15:15 am
content: Quote from: themadhippy on May 17, 2024, 01:24:37 amI get the overall concept. It's the finer details that somewhat elude me I think I just need to get a a circuit together and play with it. Thank you for that cool simulation. I've played with that simulation tool in the past I think it is incredibly underrated for what it is.