The perils of.. using breadboards (was.. of using any old schematic off the web) - Page 1
Forum section: electronics / projects

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 24, 2015, 10:53:18 am
content: I just knocked up a negative voltage generator with a 555 and simple capacitive voltage inverter on the output. To be honest I blindly copied the design off the web.So with a 1M load (the multimeter), yay -12v as expected. Not bad for a "I can't be bothered to design something properly" job.Let's try 20mA load which is a respectable amount of load so on goes a 560 ohm resistor. 21.4mA but close enough.Moral of the story: don't just copy anything off the web and assume it works nicely.EDIT: See later. The schematic is fine...

author: SeanB
author_rank: Super Contributor
timestamp: May 24, 2015, 11:36:36 am
content: I never got a 555 to go like that. Either it detonated and blows itself to bits or just sits there and does nothing. I did try running a ultrasonic generator using a 555, and used the TO100 can versions, so I could put a heatsink on it, I knew it was going to get hot driving essentially a 100n capacitor at 40kHz. It did, but survived.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 24, 2015, 11:41:45 am
content: Indeed same. It's why I decided to photograph it. Amazingly while it was smoking away it was delivering 9v @ 20mA so it was actually working. Going to stick a big emitter follower on a fresh one later.The smoked 555 still works as a timer as well which is impressive. Binning it though as the case is cracked. Not sire how much magic it lost.This is interim while I wait for some tl7660 devices to turn up.

author: Zero999
author_rank: Super Contributor
timestamp: May 24, 2015, 11:53:39 am
content: Care to post a link to the website?Was the breadboard damaged by the heat?

author: wagon
author_rank: Frequent Contributor
timestamp: May 24, 2015, 11:58:12 am
content: I had one of those blow up like that. Lump of charcoal....

author: Halvmand
author_rank: Regular Contributor
timestamp: May 24, 2015, 12:01:42 pm
content: I had the almost exact same experience yesterday.555 timer for negative rail. While testing it with different loads, the 555 gave up it's smoke.Turned out to be a misplaced 3,3 ohm resistor instead of the 330 ohm my box indicatedDon't always trust your parts boxes.What's wierd is your's crapped it self at 20 mA. Mine delivers 50mA without ripple and a 470 uF output cap while the temp is <50 deg C.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 24, 2015, 12:03:28 pm
content: Quote from: Hero999 on May 24, 2015, 11:53:39 amhttp://www.csgnetwork.com/ne555c1.htmlBreadboard was a little melted and burned. I tend to do all my first attempts at stuff on a cheapy breadboard rather than my nice wisher one as I have no intention of nuking that

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 24, 2015, 12:10:14 pm
content: Quote from: Halvmand on May 24, 2015, 12:01:42 pmYeah thats what I was hoping for. I need a simple -/+9v supply to run an op amp circuit off. I dont have the luxury of a working dual rail supply (well I do have an HP6236b but the tracking isn't working well and the caps are bad). Plus I'm trying to standardise on 12v sources due to a potential move to a boat.I checked the whole thing three times over before I powered up and checked all values. I've got a few 555s left - will attempt another go later.I've drafted a design with just transistors using a multivibrator, follower, diode-cap inverter and two simple regulators with zeners so will try that as well.Its all fun even if the remainder of the family are complianing about smoke inhalation

author: Zero999
author_rank: Super Contributor
timestamp: May 24, 2015, 12:17:56 pm
content: That circuit doesn't look too bad. I certainly would not have expected it to fail like that. Perhaps the 555 had already been damaged?Use lower value capacitors (try 10µF), add some decoupling and a 10nF capacitor from pin 5 to 0V. There should be no need for booster transistors at this low current.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 24, 2015, 12:19:29 pm
content: Was a fresh 555 straight out of a tube. Thanks for the suggestions - will look at those too.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 24, 2015, 12:36:24 pm
content: Cool thanks for suggestion.

author: Howardlong
author_rank: Super Contributor
timestamp: May 24, 2015, 12:38:26 pm
content: Moral: always use an appropriate current limit on your supply.Too many tales of my own that I now do that by default nowadays.I still have these little bugger ups though, particularly on power supplies.It works the other way too. You set current limit to what you think is appropriate on an MCU project, then spend two hours trying to figure out why it doesn't work when you turn the clock up to 11.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 24, 2015, 12:46:32 pm
content: Agree entirely. This was powered off 8xAA batteries which can shift a ton of current. I usually stick a 1W 470 ohm resistor in series with the supply but I didn't todayProblem I've got is I've got the kit (I have a working TTi PL330 supply) but no space to set up a bench at the moment.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 24, 2015, 12:48:20 pm
content: That's pretty strange. By an odd coincidence I happen to have the exact same circuit, from the exact same source, that I built up some weeks ago. Here it is with a 330 ohm resistor as load, 27 mA. No sign of misbehaviour from the 555, cool to the touch. (NE555P flavor)Powered by my bench supply at 12 volts.Is it possible that you made some mistake in your breadboarded circuit? Have you tried another 555 from the same batch?

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 24, 2015, 12:56:23 pm
content: I checked the circuit a few times. Plan is to rebuilt it with different components later and see what happens. I've bagged this entire BOM as suspect. I've got some different 555s and plenty of stock parts left.Human error is always possible. However it did work fine with no load which is weird.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 24, 2015, 01:01:24 pm
content: Here is mine with 13.5 V input, 200 ohm load. Perhaps the 555 is now running slightly warm... but maybe it's just warmed up from my finger. It is definitely not overheating. The load resistor is definitely heating but the 555 is not.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 24, 2015, 01:08:33 pm
content: Interesting. Will have another go later.Thanks for the test cases

author: SeanB
author_rank: Super Contributor
timestamp: May 24, 2015, 01:13:47 pm
content: Next time run it with a 1R to 10R resistor connected in series with pin 3, to reduce the current charge into the capacitor. As well place 1000uF directly across the 555 ( pins 1 and 8 ) to decouple the rather massive current spike when switching. The series resistor increases the output impedance of the supply but will protect the 555 output stage from the high current charging of the capacitor.edit to fix the SMF engine from thinking the close parenthesis was an emoticon.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 24, 2015, 01:20:07 pm
content: You're welcome. I've now tried several other flavors of 555:NE555PNE555NSA555PThese all work about the same, no sign of undue heating, output current through 200R load 47-48 mA (13.5 VDC in)TLC555CPOutput current dropped to 28 mA through 200R load (13.5 VDC in) but still no heating.I want to emphasize that I am using the _exact same_ circuit from the _exact same_ website as linked above.

author: Zero999
author_rank: Super Contributor
timestamp: May 24, 2015, 01:30:19 pm
content: Quote from: smjcuk on May 24, 2015, 12:19:29 pmWhere did you get them from?

author: atferrari
author_rank: Frequent Contributor
timestamp: May 24, 2015, 01:30:53 pm
content: Old schematic does not mean necessarily "wrong".How did you managed to get it still smoking and have time to take the picture. Quick reflexes, man!!

author: paulie
author_rank: Frequent Contributor
timestamp: May 24, 2015, 01:37:39 pm
content: I have also used a similar circuit many times with no hint of failure. Besides 555 a variety of other drivers from gates to MCU pins. Assuming no wiring error then almost certainly caused by intermittent plug-board contact. There are several points in this circuit that will cause self destruct if opened even briefly.I stopped using those years ago. IMO strictly for the beginner/tarduino crowd who need the education (generally what NOT to do). Contrary to urban myth, solder/deadbug is actually quicker and more convenient in addition to being a cheaper and infinitely more reliable method.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 24, 2015, 01:40:34 pm
content: Purchased from CPC/Farnell so not dodgy eBay ones.My other half was taking eBay sales photos so I snagged the camera off her quickly.Thanks for the further suggestions. Incorporating them into mk2 smoke machineEdit: this could be breadboard actually. Some of the contacts are knackered in this one. Will build mk2 Manhattan style. Recent experiment with building in that style is holding up nicely (AF gen)

author: paulie
author_rank: Frequent Contributor
timestamp: May 24, 2015, 02:29:20 pm
content: One alternative is to use CD4069 or similar part. A bit less rugged than 555 but fewer external components and gets you more voltage and current.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 24, 2015, 04:09:41 pm
content: Circuit's smoking... I know, let's take a picture of it first, before shutting off the power or anything...Moral of the story, RTFDS.Tim

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 24, 2015, 04:22:09 pm
content: Blowing up stuff is half the funOk so after a couple of hours of playing with this I've come to the conclusion: yes it was the sodding breadboard. I found that the moment you apply pressure on one part, two of the rows shorted out. They happen to be the ones that would short the output to ground meaning it sinks as a short, latches down and goes phut. The output voltage still stays high due to the size of the capacitors. I went round the entire board with a multimeter and two pins to found this out.So the thread title should be, The perils of using a breadboard. If any moderators fancy changing it, please do.So I played around with the component values and found a suitable operating point. I built the entire thing ugly style this time as well:Running that into a 470 ohm load which sinks ~20mA of current shows the following outputs which is fine. I'm drawing 10mA from this so I'm going to stick a small linear reg on the end of it as well to float the voltage at a reasonable level. Meters show source current and output voltage.And a hat tip to Bob Widlar, the breadboard has been dealt with appropriately:Thanks to paulie for the education which was very valuable here

author: paulie
author_rank: Frequent Contributor
timestamp: May 24, 2015, 05:11:31 pm
content: LOL. Yes, THAT's the ticket. Are those UT33? If so very good meter. And that is proof it's better to buy a couple low cost instead of taking out a loan for one bulky overpriced "real" meter.Quote from: T3sl4co1l on May 24, 2015, 04:09:41 pmDatasheets are for GIRLS!!! Real men use the wire 'n fire method. The trick to that approach is never buy just one component but get a whole bag of the damn things.

author: c4757p
author_rank: Super Contributor
timestamp: May 24, 2015, 05:26:13 pm
content: Quote from: smjcuk on May 24, 2015, 04:22:09 pmIt ain't Widlarized until it's powder!

author: IanB
author_rank: Super Contributor
timestamp: May 24, 2015, 05:46:26 pm
content: Quote from: smjcuk on May 24, 2015, 04:22:09 pmNo need for a mod. Just edit the first post and change the title.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 24, 2015, 06:06:52 pm
content: Quote from: paulie on May 24, 2015, 05:11:31 pmYes they are indeed UT33As. Lovely meters - cheap and reliable.Quote from: paulie on May 24, 2015, 05:11:31 pmExactly this. If there isn't the burning acrid smell of semiconductor or resistor in the atmosphere you haven't learned anything.As for powdering the breadboard, my piddly little hammer didn't have enough watts.

author: dom0
author_rank: Super Contributor
timestamp: May 24, 2015, 07:38:04 pm
content: Quote from: smjcuk on May 24, 2015, 06:06:52 pmMore like you not having enough watts

author: atferrari
author_rank: Frequent Contributor
timestamp: May 25, 2015, 05:17:59 am
content: Quote from: paulie on May 24, 2015, 01:37:39 pmYes. Time "lost" in planning the distribution even in perfboard and then soldering ends being less than chasing random "failures" in a protoboard. These have also an awful distributed capacitance.A Month ago, a transistor, refused to switch in about 2 usec until properly soldered in perfboard. Little by little, my basic proof of concept are all soldered.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 25, 2015, 09:22:08 am
content: I really can't do perfboard. Just doesn't work for me. I'm probably doing it wrong. Some people seem to use component leads for tracks but I can't get on with that approach as I switch out components a lot. I've settled on (as of yesterday), Jim Williams style prototypes then Eagle+OSHpark. I've got three perfboards here; one burned to death and two unused.

author: tggzzz
author_rank: Super Contributor
timestamp: May 25, 2015, 09:33:20 am
content: Quote from: smjcuk on May 25, 2015, 09:22:08 amWhy don't youdesignthe circuit?On second thoughts, if you use a breadboard with its unpredictable parasitic capactiance, inductance, and resistance, you probably can't design a circuit.Throw the damn things out, save yourself time and money, and get a sense of accomplishment when your circuit works according to theory and your design.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 25, 2015, 11:42:47 am
content: I do design the circuits...In this case I was purely being lazy. TBH breadboards have been little trouble for me under 4MHz or so over the last 20 years. This is the first identifiable failure caused by one.I'm using neither perfboard or breadboards now. Perfboard is inflexible and requires too much effort. Breadboard is unreliable. So dead bug/Manhattan. Seems to be the best compromise. When it works, over to PCB.For ref this entire design is scrapped now. I've designed something far more efficient on paper using discretes. 64KHz multivibrator, buffer, inverter, two 10v +/- regulators. No ICs. Just transistors, zeners, diodes, caps and resistors. 22 components for the entire solution.

author: Zero999
author_rank: Super Contributor
timestamp: May 25, 2015, 12:07:33 pm
content: Quote from: smjcuk on May 25, 2015, 09:22:08 amI'm not a fan of perfboard either.My advice is when you do use perfboard, don't use the component leads to make connections. Use thin lacquer coated wire, the kind you can just solder directly to. It's much easier. Any components you think you may change can be socketed.I prefer stripboard for prototypes. I'm not a fan of breadboard but use it occasional for small things.

author: tggzzz
author_rank: Super Contributor
timestamp: May 25, 2015, 12:12:32 pm
content: Quote from: smjcuk on May 25, 2015, 11:42:47 amI agree, except that I use perfboard for up to 4 components or where I need a little mechanical strength.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 25, 2015, 01:06:28 pm
content: I'm using offcuts of stripboard glued to the PCB blank for that sort of stuff. I assume there is no mechanical stability to start with after having a toddler attempt to kill an entire box of my stuff

author: tggzzz
author_rank: Super Contributor
timestamp: May 25, 2015, 02:05:06 pm
content: Quote from: smjcuk on May 25, 2015, 01:06:28 pmYou used to be able to buy that kind of thing, whit varying track width for different characteristic impedances. Very useful for RF stuff. The radio hams still use such techniques as a matter of course.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 25, 2015, 02:21:28 pm
content: Yeah I've got the ARRL handbook here and read about that. I'm trying to stay under 20MHz as it's a bugger above that. The company I used to work for was all microwave RF stuff. Waveguides, cavity resonators and the like. Ugh couldn't be bothered with all that.

author: Howardlong
author_rank: Super Contributor
timestamp: May 26, 2015, 11:54:10 pm
content: FWIW I do every construction method under the sun bar wire wrapping.It depends on the situation. For almost every MCU project that has a DIL part I'll use a breadboard or perfboard, and if there's some nastiness like SMPS or high speed mixed signal then it's either Manhattan/dead bug or I design a board. Sometimes it's a hybrid with the MCU still on breadboard. For larger prototypes with large SMD devices, I tend to use Schmartboards or other breakout boards together with the odd mini custom board as appropriate. Schmartboards are pretty good because they have ground planes making decoupling and ground connections easy with 0603 caps and 0R resistors.For HF and below with SMD parts, it's either perfboard or I make up a board. VHF and above I always make up a board, too much time wasted trying to make any other way work IMHO.I realise that there's a tendency to complain about breadboards, but I rarely have a problem with them and I do use them pretty much every day: I can have a basic initial rubber stamp DIL PIC project up and debugging in 10 minutes, but I am geared up for exactly that scenario as it happens so frequently. The trick is knowing when to move off the breadboard... and I'd say a 20mA charge pump really oughta work on a breadboard, so I don't know what to make of what happened. Indeed I made a charge pump last week from an oscillating PIC pin to aid bootstrapping a mosfet gate, no problems at all, although it was only a few hundred uA rather than 20mA.Irrespective, it's time to get out that current limiting PSU of yours!

author: kolbep
author_rank: Frequent Contributor
timestamp: May 27, 2015, 12:30:13 am
content: I had a 555 and 4017 blow their lids into the ceiling and across the room.Hint: if you do not know enough about capacitive power supplies, you DO need the Zener diode....Come to think of it, a pic also suffered the same fateThat is why it is only linear power supplies for me