RESET push button really necessary or ever used for products? - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: October 30, 2024, 03:59:09 am
content: Hi,just curious....for years I added a reset push button (for the micros MCLR pin) in the products for various customer, but to be honest I don't think it has ever been used once because people just turn off then on the entire equipment.Does anybody ever add reset button in products where the entire system is running ONLY if the micro is running? i.e. if the entire system is off (and safe) when the micro has no power.If so, why? What are the advantages and practical uses f having it?Thank you

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 30, 2024, 04:09:35 am
content: There are multiple cases either way :We did work for Alarm companies, and they specified a power-removal watchdog.That covers a lot more locked-up cases than a reset pin, which is better labeledreset requeston some parts.Energy from close by lightning strikes can latch-up some parts, which a MCU reset pin has no hope of correcting.Systems with contained batteries often have some 'reset hole', as power removal on those is not simple.

author: Smokey
author_rank: Super Contributor
timestamp: October 30, 2024, 05:37:48 am
content: I put a place for the button on the PCB, but I almost never actually install it for production boards.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 30, 2024, 07:10:21 am
content: mcu resets, or equipment are neededi have one with many people use, and they have a tedency to f... things up, i have to forcefully reset it once in a while, but the hard ways, have to delete config files in it thru a console ...The latest iteration now has a full reset on 5 secs hold ....eh eh i asked for this one ..

author: Siwastaja
author_rank: Super Contributor
timestamp: October 30, 2024, 07:53:52 am
content: Almost never found any use for microcontroller reset. It would be pushed in rare troubleshooting procedures in which case it is much easier to instruct users to plug off power and plug it in again, which has the added advantage of resetting "everything else" on the board too.It would make more sense to add a generic push button to GPIO pin so that you can assign it a more complex purpose when needed. Something reset-like, "reload configuration" or "run self-check" or whatever.

author: SteveThackery
author_rank: Super Contributor
timestamp: October 30, 2024, 10:00:15 am
content: I think there is a case for a push-and-hold reset function. Not connected directly to the microcontroller's reset pin, because that's not much different from a power cycle. Rather, as a way of initiating a "factory reset" feature which dumps all the "learned" parameters and returns it to its out-of-the-box state.

author: PGPG
author_rank: Frequent Contributor
timestamp: October 30, 2024, 10:11:19 am
content: In 80s/90s when microcontrollers didn't had integrated brown-out detection and watchdog I used RESET pin to force reset on power on, but never used any reset push-button.Since I don't remember how long I don't use external reset as self contained brown-out does the job.

author: Haenk
author_rank: Super Contributor
timestamp: October 30, 2024, 10:21:59 am
content: That's more of a "reset to factory defaults" than "restart" today, I guess.

author: CaptDon
author_rank: Super Contributor
timestamp: October 31, 2024, 01:16:51 am
content: Yes,we included them, much like the ones on laptops. A non-evident little hole in the case with a click detent PCB mounted push to reset button. Why, because power line glitches, nearby lightning strikes and dry atmosphere static sparks can crash boards with microprosessors and sometimes even the watchdog can get fooled. We need to include the "Insert paperclip here" forced reset.

author: ricko_uk
author_rank: Super Contributor
timestamp: October 31, 2024, 12:00:26 pm
content: Thank you all for the feedback.For those of you who say that they include them, going back to my OP, you obtain the exact same result by switching off and on the equipment (in the scenarios I mentioned), so I still don't understand the advantage.For example @CaptDon mentioned that power lines glitches, lightning etc can crash the board, but what does the rest button achieve that powering off/on the board does not?Thank you

author: tszaboo
author_rank: Super Contributor
timestamp: October 31, 2024, 12:13:58 pm
content: I had them previously. The systems we were selling were integrated, complex. You had dozens of PCBs each with their own microcontroller, and one power switch. Our customers were running tests on them that lasted sometimes months, you wanted to be able to reset individual boards without affecting the other ones.Or you would want to reset something and keep the external SRAM.Or reset the microcontroller to invoke a bootloader, without powering off the USB transceiver thus disconnecting it from your PC. Some bootloader won't even work if you don't do it that way.So there are some reasons to do, depends on the product you make.

author: ricko_uk
author_rank: Super Contributor
timestamp: October 31, 2024, 12:21:46 pm
content: Yes, all fair points.I was thinking about simple products with just one micro and as mentioned in the OP, no external "dependencies" i.e. the whole system runs only when the micro is running.Thank you

author: PGPG
author_rank: Frequent Contributor
timestamp: October 31, 2024, 12:27:43 pm
content: Quote from: ricko_uk on October 31, 2024, 12:00:26 pmIt is not a question what reset button achieve that powering off/on board does not, but if it is easier for user to use paperclip to reset laptop (it was@CaptDonexample) or to open its case and find the battery to disconnect it.

author: eleguy
author_rank: Regular Contributor
timestamp: October 31, 2024, 12:37:48 pm
content: Reset button is more than useful when doing development. At least my code seems to get stuck now and then.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 31, 2024, 12:39:48 pm
content: Quote from: CaptDon on October 31, 2024, 01:16:51 amThis make no sense. MCU reset pin is completely different to what those "paperclip holes" in consumer devices do. They are mainly for resetting to factory settings; the whole point is they do something totally different than cycling power, because every user can cycle power. They are not wired up to reset pins of any CPU or MCU, they connect to an IO pin which triggers a specialized piece of software (like I suggested in my earlier reply). This code would, for example, override all user settings with factory defaults and then restart the device.Stuck laptops are normally turned off by holding the power button for 5 seconds, after which you can restart as usual. I'm not aware of a laptop with a paperclip hole but I'm 99% certain the switch behind the hole is not directly wired to any reset signal of any microcontroller or processor.

author: PGPG
author_rank: Frequent Contributor
timestamp: October 31, 2024, 01:05:29 pm
content: Quote from: Siwastaja on October 31, 2024, 12:39:48 pmI'm not sure what are these peperclip holes rests for but if the consumer device has any user interface than resetting to factory settings need not any reset pin - user can select the right menu item.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 31, 2024, 01:11:58 pm
content: Quote from: PGPG on October 31, 2024, 01:05:29 pmThese holes are usual in devices which have no physical menu available. Like a home router / wifi access point. If you lose the admin password or configure the network weirdly, you can't access the "menu". Then you reset it to factory settings.

author: SteveThackery
author_rank: Super Contributor
timestamp: October 31, 2024, 01:19:27 pm
content: Quote from: PGPG on October 31, 2024, 01:05:29 pmOnly if the UI is actually working. Sometimes, bad parameters in flash memory can render a product unusable. In that case a press-and-hold "factory reset" feature is essential.We need to be clear about the difference: a switch connected to the reset pin of the microcontroller does much the same thing as a power cycle, so is usually pointless. A press-and-hold button to reset any flash-based parameters (ie a factory reset) is a different thing and might be essential.Finally, if it is not possible to power-cycle the microcontroller due to it being permanently connected to an internal battery, then a switch connected to the reset pin is probably essential.It is a good design discipline to build a degree of resilience into a product. "Resilience" in this case being the facility for the end user to restore the product to working order if it somehow enters an illegal state.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 31, 2024, 01:43:03 pm
content: Quote from: SteveThackery on October 31, 2024, 01:19:27 pmOne obvious example would be password lockout of the configuration menu, very typically available to prevent unauthorized people accidentally or purposely changing settings. If you then lose the password, you would use the paperclip. Maybe it would physically hidden in a hard-to-access location. It's not security against true malice - anyone can use the paperclip after all -, but security against unnecessarily zealous workers/customers changing settings on a whim.

author: ebastler
author_rank: Super Contributor
timestamp: October 31, 2024, 01:54:49 pm
content: I have used a Reset button as a simple soft power switch a couple of times: Use a "magic number" in non-initialized RAM to let the microcontroller check whether it was previously running or switched off. Depending on the previous state, either put the system to deep sleep/standby or boot it up.This allows you to also power off under software control e.g. after a certain inactivity period, and has the option of storing operating parameters in EEPROM (or flash, if that's all the µC has) before really shutting things down. And the reset will ensure that the system always responds, even in case the software got stuck before.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: October 31, 2024, 03:44:42 pm
content: Texas Instrument calculators have a reset button. On my go-to scientific calculator, the TI-34, the reset button is under the case though in the form of only carbon tracks for a carbon soft button. You'll have to short those to reset the calculator.On higher end calculators like the TI-84, the reset button is built-in.

author: Salitronic
author_rank: Contributor
timestamp: November 02, 2024, 11:33:18 am
content: Normally one reason you might need a reset button (apart from development purposes) is if you want a way to jump to some kind of bootloader on a battery powered device. But even that is not normally done with just a reset button. In a commercial design a reset button is rarely included.

author: CaptDon
author_rank: Super Contributor
timestamp: November 02, 2024, 01:42:16 pm
content: Our 'secret' reset button WAS connected to the watchdog / CPU reset and WAS NOT a flash recovery. What does that do that a simple power cycle won't do, actually nothing! Did you ever think that in industrial settings the 'power cycle' could be a disconnect mounted on the wall 10 feet away? Those machines typically have an ESTOP and not a handy power switch. And maybe during maintaining or calibration or indexing procedures it might be handy to have a local reset? Not every hidden reset on laptops does a factory restore of bios!! It helps get past the stupid 'soft switch failure' when the system crashes and hangs and you can't shut the laptop off. Insert paper clip OR remove external power AND take the battery out, oh wait, what about the ones where you can't take the battery out? Well, then you hold the secret button handshake for 30 seconds in some cases. Yes, there are certain cases where a reset button is very handy and certain cases where no one should have access to any form of reset. It just depends on the product.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 02, 2024, 04:37:22 pm
content: Quote from: CaptDon on November 02, 2024, 01:42:16 pm... but it's still not connected to the CPU or MCU reset pin.Really, read the opening post of the thread you are replying to.

author: Kim Christensen
author_rank: Super Contributor
timestamp: November 02, 2024, 05:47:11 pm
content: I've used the reset input as a start button on a small MCU with limited pins. User pushes the reset/start button, MCU runs it's code, and then enters sleep mode.

author: CaptDon
author_rank: Super Contributor
timestamp: November 02, 2024, 08:20:59 pm
content: I could have connected it to the MPU reset directly BUT the watchdog WHICH IS CONNECTED DIRECTLY TO THE MPU RESET has a built in delay for power up stability AND an external reset input which will trigger the power up reset timer. And yes, on earlier products prior to incorporating watchdogs we always connected the reset push button directly to the MPU. The MPU reset consisted of a timing capacitor to ground, a timing pullup resistor to +5, a drain diode to remove the charge from the capacitor during a brief power fail thus insuring a good reset after a power glitch and the manual forced reset. These were 8085 based systems. Dedicated watchdog+power rail monitor combo chips came along long after the release of the 8080/8085/6800 stuff nearly all of which had a front or back panel reset push button tied directly to the MPU or possibly through a buffer I.C. to protect the MPU reset pin from static electricity coupled into the reset button. The problem with watchdogs is that usually during software development you have to jumper two pins on the PCB to disable the watchdog, otherwise the system keeps resetting anywhere from every ten seconds to every two minutes.