Post by thread:[PIC] Dying PICs

I have a project I set aside a few months ago in a "mostly done" state. I finally got back back to it today planning to fiish it up. When I powered it, it seemed completely dead. After 30 mins of troubleshooting, I decided to see if I could read the PIC (16F628) in my PicStart plus (using MPLAB IDE 7.21). It showed up in a weird state, the config bits wrong, including code protect set to all (I don't use code protect during development). I tried blanking the device which doesn't generate any message then when I try to program it, MPLAB says: "Program Memory or EEPROM Data is protected. Reprogram the entire part. If "Auto select memory areas and range" on the Memory Ranges tab of the programmer settings is enabled, it must be disabeled before proceeding." Even with the auto select feature disabled. I decided the chip might have been damaged, so I got out a new 16F628, programmed it and put it in the project. It worked fine for about 20 seconds, then the PIC got so hot it would burn me if I touched it for more than a fraction of a second and the project stopped working. When I put the PIC back in the picstart it behaves exactly as the original chip that wasn't working. When I put a damaged pic back in, the project is totally dead, but the pic stays cold. Any ideas what could be going wrong here? It was working fine when I shelved it a few months ago. I spent a lot of time looking for loose connections that might be shorting, and the only possibility is that I grounded pin 16. This is RA7/OSC1/CLKIN. My oscillator is set for INTRC/IO. I've fixed the loose connection that might have caused the short, but I really don't want to blow another chip, especially since I only have one F628 left. Jason

> When I put a damaged pic back in, the project is totally dead, > but the pic stays cold That's because it got as munted as it could be before you took it out. Probably it latched, drawing a lot of power and heating up. When you turned the power off to remove it, that fixed the latching but the damage had been done > Any ideas what could be going wrong here ? Is the power on the correct way ? (It happens) Are there any floating inputs, by accident or oversight ? Is there any other damage ? eg moisture, corrosion Is there any possibility of voltages below 0V getting on to pins ? I've sent a couple to PIC heaven with sub-0V spikes. They also got very very hot before they, before they...sniff > I've fixed the loose connection that might have caused the short, > but I really don't want to blow another chip, especially since I > only have one F628 left Might not be a short - something could be open, leaving a pin vulnerable to damage. I'd suggest checking the board very thoroughly (which you probably have done already but check it again anyway, and methodically). Then put power on it, without the PIC in, and measure around. To state the obvious, there is a logical reason why this is happening Maybe someone should pop around and take your last PIC into protective custody.................

From: "Jinx" <spam_OUTjoecolquittTakeThisOuTclear.net.nz> Sent: Tuesday, October 18, 2005 1:19 AM >> Any ideas what could be going wrong here ? > > Is the power on the correct way ? (It happens) Yep, first thing I checked :) > Are there any floating inputs, by accident or oversight ? There is one floating input. The wire that shorted pin 16 to ground was supposed to be tying pin 17 (RA0, configured as an input) to ground through a 1k resistor. The way the wire broke lose left pin 17 floating for sure, and might have grounded pin 16. Leaving an input floating can fry the chip? > Is there any other damage ? eg moisture, corrosion There doesn't seem to be on the original chip, and the second one is brand new. > Is there any possibility of voltages below 0V getting on to > pins ? I've sent a couple to PIC heaven with sub-0V spikes. > They also got very very hot before they, before they...sniff I'm using an unregulated DC wall wart...so I don't think so, but I don't know 100%. > Maybe someone should pop around and take your last > PIC into protective custody................. I guess my next order to glitchbuster will be a lot sooner than I thought :( Jason

> > Are there any floating inputs, by accident or oversight ? > > There is one floating input............. > Leaving an input floating can fry the chip? http://www.piclist.com/techref/logic/xtrapins.htm The author says (about a floating input) - "The power loss due to rapid switching of a tri-stated input pin may be significant. Disclamer: I do not have hard data on this, but I believe I'm correct. Rapid switching will not fry the chip" That is unproven AFAIK, but maybe Microchip have documentation. In either case, as you know, best not to let pins float > > Is there any other damage ? eg moisture, corrosion > > There doesn't seem to be on the original chip, and the second one > is brand new I was thinking more of the board > > Is there any possibility of voltages below 0V getting on to > > pins ? I've sent a couple to PIC heaven with sub-0V spikes. > > They also got very very hot before they, before they...sniff > > I'm using an unregulated DC wall wart...so I don't think so, but > I don't know 100% Noise (eg ripple) coming from the PSU "probably" won't do any harm, but spikes, especially sub-0V, coming from other sources into pins can fatally damage a PIC. The reason is that the internal diode conducts and the pin's circuitry burns out. The cure for this is to protect the internal diode with an external Schottky diode, which will conduct before the internal one and so shunt the spike away Now, that's assuming the problem you have is noise. What other components are there ? motor ? relay ? solenoid ? or maybe even lighting ?

From: "Jinx" <.....joecolquittKILLspam@spam@clear.net.nz> Sent: Tuesday, October 18, 2005 1:52 AM {Quote hidden}>> Leaving an input floating can fry the chip? > > http://www.piclist.com/techref/logic/xtrapins.htm > > The author says (about a floating input) - > > "The power loss due to rapid switching of a tri-stated input pin > may be significant. Disclamer: I do not have hard data on this, > but I believe I'm correct. Rapid switching will not fry the chip" > > That is unproven AFAIK, but maybe Microchip have documentation. > In either case, as you know, best not to let pins float I know it's best not to let pins float, but this was due to a wire that broke loose. So far it's the only thing I can see being wrong, but I can't see how it can damage the chip, and you seem to be saying it shouldn't too. >> > Is there any other damage ? eg moisture, corrosion > > I was thinking more of the board There's no damage I can see beyond the wire and resistor broken loose (it was a temporary modification and I was finally going to redo it more cleanly nad neatly with the permanent parts). There's no visible corrosion, etc. > Now, that's assuming the problem you have is noise. What > other components are there ? motor ? relay ? solenoid ? or > maybe even lighting ? There's about 1 amp of LED's being driven off the PSU controlled through transistors from the PIC. There are diodes between the transistor and the power rails. It might be causing a fair bit of ripple, but I don't think a negative voltage on any pin is possible. Jason

Hi Jinx. > > > Are there any floating inputs, by accident or oversight ? > > There is one floating input............. > > Leaving an input floating can fry the chip? > www.piclist.com/techref/logic/xtrapins.htm > The author says (about a floating input) - > "The power loss due to rapid switching of a tri-stated input pin > may be significant. Disclamer: I do not have hard data on this, > but I believe I'm correct. Rapid switching will not fry the chip" I believe that rumors about switching tri stated pin will cause chip damage are complete nonsense. Floating pins are proved to cause extensive current sonsumption ( in battery application power saving modes ) but not to extend frying the chip out. I rather check with scope if electrolytic capacitor in power adapter has dried out and power adapter is out of specs or pulsating above the +5 power specs. Output pin shortages to +5 power or ground is seconds thing to check. > Noise (eg ripple) coming from the PSU "probably" won't do > any harm, but spikes, especially sub-0V, coming from other > sources into pins can fatally damage a PIC. The reason > is that the internal diode conducts and the pin's circuitry burns > out. The cure for this is to protect the internal diode with an > external Schottky diode, which will conduct before the internal > one and so shunt the spike away I would recomend to place small resistor i.e. 200 OHm is series with PIC inputs connected to outside 0 to 5V signals to limit ingoing current to prevent that possibility in most situations ( for higher possible input voltages resistor should be increased ) After all if ESD is an issue ( all mystical deaths when winter time is approaching ) ESD protection elements should be used on the board entrances. WBR Dmitry.

From: "Dmitriy Kiryashov" <vze27bymKILLspamverizon.net> Sent: Monday, October 17, 2005 6:19 PM > I rather check with scope if electrolytic capacitor in power adapter > has dried out and power adapter is out of specs or pulsating above > the +5 power specs. Output pin shortages to +5 power or ground is > seconds thing to check. Since it's a sealed wall wart, I can't get at the cap inside it. It reads around 7.3 volts no-load (it's rated at 5v, 2 amp). One of the first thing I checked was output pin shortages to ground. I did find that pin 16 (RA7/OSC1/CLKIN) might have been grounded. Actually it's a bit more complicated on closer consideration. All of port A is set for digital input. I'm using RA0 in my project with the rest left floating (bad design I know, but It's a retrofit on a pre-existing board which limited my options). This did work fine during about 48 hours of continuous on-time a few months ago. It was originally based on a F84 with an external RC circuit which is still physically connected to the OSC1 pin. The F628 I'm using is configured for INTRC/IO, and I'm not doing anything with the other port A pins in software. > I would recomend to place small resistor i.e. 200 OHm is series > with PIC inputs connected to outside 0 to 5V signals to limit ingoing > current to prevent that possibility in most situations ( for higher > possible input voltages resistor should be increased ) This will be quite hard to do as it's on a pre-made PCB. How likely is this to help? > After all if > ESD is an issue ( all mystical deaths when winter time is approaching ) > ESD protection elements should be used on the board entrances. I did think ESD was a strong possibility for the first blown chip. I was extra careful in my handling of the second one. Jason

MCLR is going through 100k to Vcc. There is no reset switch. I just tried powering it again to take some voltage measurements with the first blown chip. It got super hot again, worse than before since I wasn't feeling it and I didn't notice until I started smelling it. I know for sure that the clkin pin was not shorted to anything this time though. If 2 outputs from the driver transistors get shorted, it should not cause a problem for the pic; just the transistors will get hot, right? (I'm trying to narrow down where to look) Jason {Original Message removed}

Measure +5 supply with _scope_ right on the PIC Vcc pin. ( no pulses above specififed in 628 datasheet supply voltage ) It is reasonable to use 7805 regulator if you didnt do so yet. Question : Anybody heard of PIC heating up not being properly reset or when no clock is applied ? Jason wrote: {Quote hidden}> > MCLR is going through 100k to Vcc. There is no reset switch. > > I just tried powering it again to take some voltage measurements with the > first blown chip. It got super hot again, worse than before since I wasn't > feeling it and I didn't notice until I started smelling it. > > I know for sure that the clkin pin was not shorted to anything this time > though. > > If 2 outputs from the driver transistors get shorted, it should not cause a > problem for the pic; just the transistors will get hot, right? (I'm trying > to narrow down where to look) > > Jason > > {Original Message removed}

I afraid you damaging the PIC like that. Use voltage regulator to supply the PIC. Jason wrote: {Quote hidden}> > From: "Jan-Erik Soderholm" <EraseMEjan-erik.soderholmspam_OUTTakeThisOuTtelia.com> > Sent: Tuesday, October 18, 2005 3:03 AM > > >> it's a sealed wall wart,... It reads > >> around 7.3 volts no-load (it's rated at 5v, 2 amp). > > > > How do you regulate/limit that down to 5V ? > > I don't :) > > > What voltage do you have with no LEDs on ? > > Around 6.2V, but that's measuring now with the problem.

>-----Original Message----- >From: piclist-bouncesspam_OUTmit.edu [@spam@piclist-bouncesKILLspammit.edu] >Sent: 18 October 2005 11:20 >To: Microcontroller discussion list - Public. >Subject: Re: [PIC] Dying PICs > > >From: "Jan-Erik Soderholm" <KILLspamjan-erik.soderholmKILLspamtelia.com> >Sent: Tuesday, October 18, 2005 3:03 AM > >>> it's a sealed wall wart,... It reads >>> around 7.3 volts no-load (it's rated at 5v, 2 amp). >> >> How do you regulate/limit that down to 5V ? > >I don't :) And there you have your problem, or at least one of them. Have a look in the PIC's datasheet under absolute maximum ratings. The 16F628 has an absolute maximum voltage on Vdd wrt Vss of 6.5 volts. This specification does not even mean the PIC will work properly at 6.5, it's just the maximum voltage you can apply without permanent damage occuring. The maximum operating voltage is 5.5 volts. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. =======================================================================

> >> around 7.3 volts no-load (it's rated at 5v, 2 amp). > > > > How do you regulate/limit that down to 5V ? > > I don't :) I think you mean "Oh no ! I don't ;-((((((((" Absolute maximum rating for a 628 is 6.5V. You're asking for trouble running it over 5.5V. The problem is that your PIC isn't taking anywhere near 2A (admittedly you're doing your very best to make it do so ;-) ) and so the voltage isn't going to drop significantly below 7.3V with a temporarily healthy PIC The LEDs can be run on the 7.3V, although the more you have on, the dimmer they'll get, but the PIC must be down at 5V-ish. The margin between 7.3 or 6.2 is too low for a 78L05, you'll have to use a low drop-out (LDO - there are a few common ones around like the LP29xx) regulator, or, as so much power is being used by the LEDs anyway, a 5V1 zener. The zener's series resistor, together with a reservoir cap on the PIC side, say a few 100uF, should give you a smooth stable PIC 5.1V Your PIC's aren't dying, they're being murdered. You, you, you .... murderer you ;-)

From: "Michael Rigby-Jones" <RemoveMEMichael.Rigby-JonesTakeThisOuTbookham.com> Sent: Tuesday, October 18, 2005 3:29 AM > And there you have your problem, or at least one of them. Have a look in > the PIC's datasheet under absolute maximum ratings. The 16F628 has an > absolute maximum voltage on Vdd wrt Vss of 6.5 volts. This specification > does not even mean the PIC will work properly at 6.5, it's just the > maximum voltage you can apply without permanent damage occuring. The > maximum operating voltage is 5.5 volts. It did work for before I set it aside for a few months. It's not my design. It's a commercial LED light show display I'm modifying because I don't like the factory designed show. All I've done is replace the original CF745 that had the code I don't like with a 16F628 with my code.

{Quote hidden}>-----Original Message----- >From: spamBeGonepiclist-bouncesspamBeGonemit.edu [TakeThisOuTpiclist-bouncesEraseMEspam_OUTmit.edu] >Sent: 18 October 2005 11:48 >To: Microcontroller discussion list - Public. >Subject: Re: [PIC] Dying PICs > > >From: "Michael Rigby-Jones" <RemoveMEMichael.Rigby-JonesTakeThisOuTbookham.com> >Sent: Tuesday, October 18, 2005 3:29 AM > >> And there you have your problem, or at least one of them. >Have a look >> in >> the PIC's datasheet under absolute maximum ratings. The >16F628 has an >> absolute maximum voltage on Vdd wrt Vss of 6.5 volts. This >specification >> does not even mean the PIC will work properly at 6.5, it's just the >> maximum voltage you can apply without permanent damage >occuring. The >> maximum operating voltage is 5.5 volts. > >It did work for before I set it aside for a few months. > >It's not my design. It's a commercial LED light show display >I'm modifying >because I don't like the factory designed show. > >All I've done is replace the original CF745 that had the code >I don't like >with a 16F628 with my code. Perhaps the PSU has died then? If there is no onboard regulation then the PSU should be of the regulated type. Either way 7.3volts is enough to damage a PIC. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. =======================================================================

Ah... The C745 can take 7.5 volts vdd in contraty to the opposing and lower 5.5 volts of the F628. That's your problem then; You where careless selecting the right pic for the right job! Sean On 10/18/05, Jason <picEraseME.....canadaspeaks.com> wrote: {Quote hidden}> > From: "Michael Rigby-Jones" <EraseMEMichael.Rigby-Jonesbookham.com> > Sent: Tuesday, October 18, 2005 3:29 AM > > > And there you have your problem, or at least one of them. Have a look in > > the PIC's datasheet under absolute maximum ratings. The 16F628 has an > > absolute maximum voltage on Vdd wrt Vss of 6.5 volts. This specification > > does not even mean the PIC will work properly at 6.5, it's just the > > maximum voltage you can apply without permanent damage occuring. The > > maximum operating voltage is 5.5 volts. > > It did work for before I set it aside for a few months. > > It's not my design. It's a commercial LED light show display I'm modifying > because I don't like the factory designed show. > > All I've done is replace the original CF745 that had the code I don't like > with a 16F628 with my code. > > >

From: "Jinx" <RemoveMEjoecolquittspam_OUTKILLspamclear.net.nz> Sent: Tuesday, October 18, 2005 4:09 AM > The 16C745 has a max Vdd of 7.5V, so it wouldn't have > died at 7.3V. It has a working Vmax of 5.25V, less than > the F628. Pretty poor design to expect it to work properly > unless the majority of LEDs were on to get Vdd down Then would you recommend I try with an F84 (that also says absolute max of 7.5V in the datasheet) which I happen to have on hand? I'm obviosuly not going to be able to get a CF745. The 16C54 and 16F54 which would be the direct replacements aren't as common.

pic@canadaspeaks.com wrote: > I decided the chip might have been damaged, so I got out a new 16F628, > programmed it and put it in the project. It worked fine for about 20 > seconds, then the PIC got so hot it would burn me if I touched it for > more than a fraction of a second and the project stopped working. This should have been a strong clue. Obviously something about your circuit is blowing up PICs. That has to be fixed before anything else. > When > I put the PIC back in the picstart it behaves exactly as the original > chip that wasn't working. Big surprise, since fried PICs can have all sorts of strange behavior. > When I put a damaged pic back in, the project is totally dead, but the > pic stays cold. Note that fuses work the same way. They get really hot, once. > Any ideas what could be going wrong here? Your circuit is frying PICs. Turn on the circuit without a PIC in there and carefully look at the voltage on all the pins. You'll probably find something very wrong. Also make really sure you're not plugging the PIC in backwards. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com

> Then would you recommend I try with an F84 (that also > says absolute max of 7.5V in the datasheet) which I > happen to have on hand ? No. You're too close to the edge. It would be much better to give the PIC the 5V it should have. It will take just a zener and a resistor. Either that or look for a PIC with "Stunt" written on it Are the transistors low-side ? ie, are their emitters to 0V and their collectors to the LEDs ? If so then a 5V PIC o/p will drive them on just as hard as at 7.3V, you'll not see any difference in LED brightness To be honest, I'd be looking for a more stable supply for the LEDs too. How are they arranged ? 2 or 3 in series or just one per transistor ? How about resistors ?

Jinx: you do not know what is a CF745 and I guess not many people know that part. It is not a 16C745! 16C745 will be too high cost for the vendors using CF745. CF745 is a special part by Microchip specifically for the Chinese market to combat the low cost Taiwanese clones. It is the same as 16C54 without the testing part to lower the cost. Apparently Jason knows this. It is not advertised by Microchip since it should not goes to the retail market. The idea is to let the vendors using the part do the tests. Regards, Xiaofan {Original Message removed}

From: "Chen Xiao Fan" <RemoveMExiaofanTakeThisOuTspamsg.pepperl-fuchs.com> Sent: Tuesday, October 18, 2005 5:32 PM > CF745 is a special part by Microchip specifically for the > Chinese market to combat the low cost Taiwanese clones. > It is the same as 16C54 without the testing part to > lower the cost. Apparently Jason knows this. I know this thanks to you :) When I first started working on this project I posted here asking what the CF745 was. From: "William Chops Westfield" <EraseMEwestfwspamspamBeGonemac.com> Sent: Tuesday, October 18, 2005 11:58 PM > You didn't accidentally switch from a regulated wall wart to an > unregulated version, did you? Easy enough to do if you read the specs > printed > on the warts and actually believe them... Nope, it's the same wall wart, the project has just been sitting on a box on a shelf for about 3 months. Nothing at all should have changed from when it was working, but clearly something did. For the people who are saying I should be using a regulated supply. You're right, but I don't think that's the problem here. The project worked in a 48 hour constant running test with the 16F628 before I shelved it temporarily. Now it doesn't work. So while I should regulate the power supply I don't think it will fix the problem, I'm pretty sure something else is blowing the chips. The second one that blew yesterday lasted about 20 seconds and blew, and while running it's got enough LEDs lit to bring the power supply voltage down. I have a few untouched versions of the project, so maybe my next step should be to start from scratch with a new one. It's just so hard to desolder the 18-pin chip.

If it's been 6 months since you last used it you may have had some change in your AC supply. An increase here due to a change in supply or operting conditions will increase the voltage out of an unregulated wall-wart. It could be as simple as operating at a different time of day. The 7.3V you are measuring is also probably an average - there may be peaks and/or transients well above this - again this can change with season, time and weather. I'd start with making sure the supply voltage is close to 5.0 and then spend more time searching in the unlikely event that this doesn't fix the problem. Once you do desolder the chip - sloder a socket in its place. That way you can almost guarantee you won't ever have to change the chip again. Richard P On 19/10/05, Jason <RemoveMEpicKILLspamcanadaspeaks.com> wrote: {Quote hidden}> From: "Chen Xiao Fan" <xiaofanSTOPspamspam_OUTsg.pepperl-fuchs.com> > Sent: Tuesday, October 18, 2005 5:32 PM > > > > CF745 is a special part by Microchip specifically for the > > Chinese market to combat the low cost Taiwanese clones. > > It is the same as 16C54 without the testing part to > > lower the cost. Apparently Jason knows this. > > I know this thanks to you :) > > When I first started working on this project I posted here asking what the > CF745 was. > > > From: "William Chops Westfield" <spamBeGonewestfwSTOPspamEraseMEmac.com> > Sent: Tuesday, October 18, 2005 11:58 PM > > > > You didn't accidentally switch from a regulated wall wart to an > > unregulated version, did you? Easy enough to do if you read the specs > > printed > > on the warts and actually believe them... > > Nope, it's the same wall wart, the project has just been sitting on a box on > a shelf for about 3 months. Nothing at all should have changed from when it > was working, but clearly something did. > > > For the people who are saying I should be using a regulated supply. You're > right, but I don't think that's the problem here. The project worked in a > 48 hour constant running test with the 16F628 before I shelved it > temporarily. Now it doesn't work. > > So while I should regulate the power supply I don't think it will fix the > problem, I'm pretty sure something else is blowing the chips. > > The second one that blew yesterday lasted about 20 seconds and blew, and > while running it's got enough LEDs lit to bring the power supply voltage > down. > > I have a few untouched versions of the project, so maybe my next step should > be to start from scratch with a new one. It's just so hard to desolder the > 18-pin chip. > > > -

Are you measuring 7.3V RMS, (average)? If so, you'll regularly be getting peaks of 10 V or so, with line noise on top of that. -->"For the people who are saying I should be using a regulated supply. You're right, but I don't think that's the problem here. The project worked in a 48 hour constant running test with the 16F628 before I shelved it temporarily. Now it doesn't work."<-- That's not evidence of anything. Could be that the act of switching it off damaged the wall wart, or damaged some component on the board. Then it just waits in the closet 6 months before you find out. Could be that the act of getting it out of the closet damaged something with a static zap. In any case.. it's all speculation. You may never find out why it failed. But what you need to do now is troubleshoot using standard procedures. The standardest procedure of all is.. use a power supply that is unimpeachable. And yes, start with a new board, with a socket for the PIC. Are there many other components? Start by adding just the PIC and nothing else, and test with the UPS (== Unimpeachable Power Supply ;-). If that works, (doesn't burn) you can add more components, etc.

At 04:52 AM 10/18/2005, you wrote: > > > Are there any floating inputs, by accident or oversight ? > > > > There is one floating input............. > > > Leaving an input floating can fry the chip? 1. Check the power connections and voltage and polarity again. DC, not AC? Within chip limits? Ground and +Vdd correct? Right PIC pins? Add a blocking diode or bridge and a current limiting resistor for continuing testing, so you don't blow more chips. Even you "think" you've checking power, you may be blind to your own assumptions. Clear your mind of preconceptions and check in detail. 2. You might consider putting in an unprogrammed PIC and seeing if it gets hot. If so, stop it within the first few seconds and pull the power. The chip should survive this. If it gets hot, you have a problem with applied power polarity and pins. 3. If the unprogrammed chip does not get hot, and the programmed one does, then you have a problem with logic and design. E.g., you ground a pin, but then declare it output in the program and pull it high. This will short the output and ruin the chip. ================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: KILLspamralspamBeGonelcfltd.com Least Cost Formulations, Ltd. URL: http://lcfltd.com/ 824 Timberlake Drive Tel: 757-467-0954 Virginia Beach, VA 23464-3239 Fax: 757-467-2947 "Vere scire est per causas scire" ================================================================

At 08:23 PM 10/18/2005, Xiaofan wrote: >Try it and you will learn more about 7805. ;-) > >A 7805 will not work with input voltage as low as 6.2V. >An LDO like LP2980-5.0 will. Actually, the real input voltage was 7+ VDC from the unloaded wal-wart. The 6.2 V was with the maximum load drawn from a blown PIC device. The 78L05 should work fine with this application. The wal-wart is rated for 2 A, so the current draw should not appreciably drop the voltage. ================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: EraseMEralEraseMElcfltd.com Least Cost Formulations, Ltd. URL: http://lcfltd.com/ 824 Timberlake Drive Tel: 757-467-0954 Virginia Beach, VA 23464-3239 Fax: 757-467-2947 "Vere scire est per causas scire" ================================================================

From: "Richard Prosser" <@spam@rhprosser@spam@spam_OUTgmail.com> Sent: Wednesday, October 19, 2005 2:15 AM > Once you do desolder the chip - sloder a socket in its place. That way > you can almost guarantee you won't ever have to change the chip again. > Richard P This one is a given. I have never soldered a chip to a board, I always use a socket. From: "Neil Baylis" <spamBeGoneneil.baylisKILLspamgmail.com> Sent: Wednesday, October 19, 2005 7:29 AM > Are you measuring 7.3V RMS, (average)? If so, you'll regularly be > getting peaks of 10 V or so, with line noise on top of that. I'm getting 7.3V DC. It's a DC power suppy. It's a DMM, so it samples, but the 7.3 is steady. > And yes, start with a new board, with a socket for the PIC. Are there > many other components? Start by adding just the PIC and nothing else, > and test with the UPS (== Unimpeachable Power Supply ;-). If that > works, (doesn't burn) you can add more components, etc. Besides the PIC, the only other components are the 8 output driver circuits (transistor, resistor, diode), the LEDs, a cap across the power supply, a resistor on MCLR to Vcc, and an RC oscillator circuit (which I ignore in INTRC/IO mode). These are all part of the original factory build. It also has a resistor from one of the previously unused/not-connected IO lines to Ground and pushbutton to Vcc that I added. From: "Robert A LaBudde" <.....ralspam_OUTlcfltd.com> Sent: Wednesday, October 19, 2005 8:59 AM > The 6.2 V was with the maximum load drawn from a blown PIC device. > > The 78L05 should work fine with this application. The wal-wart is rated > for > 2 A, so the current draw should not appreciably drop the voltage. I doubt the blown pic was drawing "maximum" load... with no LEDs lit. Under normal operation before I opened the control box, that 2 amp wall wart got very hot, as did the output transistors. There's 160 LEDs in the project, and I get the impression it draws pretty close to (if not over) 2 amps. I actually picked up a few of these quite cheaply as surplus, and I believe it was because the power supply and transistors are underrated. Part of the changes I've made are to PWM the outputs to reduce power so it won't run so hot. I still think it's pulling an average of around an amp. The output will be well below 6.2 V under normal load, but I didn't measure it when the thing was working. Besides that, I've always been told I need at least an extra 3 volts for a 7800 series regulator, so I should have at least 8 volts under load.

-->"I'm getting 7.3V DC. It's a DC power suppy. It's a DMM, so it samples, but the 7.3 is steady."<-- Have you measured it on the AC range of your DMM? You need to know how much ripple is there, as well as the average, DC voltage. With the ripple, you could easily see peaks that will damage the PIC if the DC component is 7.3. Ripple increases with load, and it sounds as though your wall wart is way overloaded. The wall wart getting hot is a bad sign. It's OK if the output transistors get hot. Instead of a 7805, you could use an LT1085 or similar LDO regulator. Also, I've got a feeling you're going to need a different power supply. Neil -- http://www.pixpopuli.com

>> I've got a feeling you're going to need a different power supply. >> In the short term, do you have any sort of regulated 5V supply that you can use for testing? A better wall-wart, lab-style supply, or even a connector into your PC's supply? This would let you find out pretty quickly if the power supply really IS the problem... I can't help but notice that the suggestions to throw in a 7805 don't match well with the fact the current supply is spec'ed at 2 amps :-) A lot of LEDs end up using a lot of current. (Perhaps your problem is even along the lines that your modified code doesn't cause the LED drivers to consume enough current to keep the unregulated supply down to a reasonable voltage...) You mentioned you have several units - do ALL the power supplies put out 7+V? It's potentially possible that the particular supply was damaged somehow... BillW

From: "William Chops Westfield" <TakeThisOuTwestfw.....TakeThisOuTmac.com> Sent: Wednesday, October 19, 2005 6:44 PM > In the short term, do you have any sort of regulated 5V supply that > you can use for testing? A better wall-wart, lab-style supply, or > even a connector into your PC's supply? This would let you find out > pretty quickly if the power supply really IS the problem... I can use my PC power supply, but I was thinking 4 NiMH AA's would work too. They should be around 4.8-5v, and able to handle 2 amps. > I can't help but notice that the suggestions to throw in a 7805 don't > match well with the fact the current supply is spec'ed at 2 amps :-) Yeah I noticed that too. I hadn't looked up the specs of the 7805's yet but I figured at least I was looking at a TO-220 with a hefty heatsink. A few volts a a couple of amps is a big amount to turn into heat. > A lot of LEDs end up using a lot of current. > (Perhaps your problem is even along the lines that your modified code > doesn't cause the LED drivers to consume enough current to keep the > unregulated supply down to a reasonable voltage...) That's an interesting idea, it's quite possibly the problem if the chip is frying due to overvoltage. > You mentioned you have several units - do ALL the power supplies put > out 7+V? It's potentially possible that the particular supply was damaged > somehow... The other units are still sealed in their retail packaging, I haven't measured their power supplies.

At 11:17 PM 10/19/2005, Jason wrote: >>I can't help but notice that the suggestions to throw in a 7805 don't >>match well with the fact the current supply is spec'ed at 2 amps :-) > >Yeah I noticed that too. I hadn't looked up the specs of the 7805's yet >but I figured at least I was looking at a TO-220 with a hefty heatsink. A >few volts a a couple of amps is a big amount to turn into heat. This is one of the things that doesn't make sense in your story. No one would drive 2 A through 200 LED's controlled by pass transistors through a linear regulator unless absolute brightness control were necessary, and even then they'd wire the transistors as current regulators instead. Otherwise, the LEDs and transistors don't need highly regulated power. The PIC does. A 78L05 on the PIC power supply should be more than sufficient. Running all the current through a 78xx regulator would just waste 30% of the power that could have been used to light LEDs instead. Driving a PIC beyond its absolute maximum voltage will cause breakdown and shorting within the chip, which could be why the voltage drops to 6.2 V from 7.3 V, and the LEDs (which are through resistors) don't light. It would also, of course, fry the PIC. Once you've determined you are violating a key endurance specification, why not fix that problem and then see what happens? Why is any more discussion necessary? ================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: TakeThisOuTralKILLspamspamlcfltd.com Least Cost Formulations, Ltd. URL: http://lcfltd.com/ 824 Timberlake Drive Tel: 757-467-0954 Virginia Beach, VA 23464-3239 Fax: 757-467-2947 "Vere scire est per causas scire" ================================================================

> > I would recomend to place small resistor i.e. 200 OHm is > > series with PIC inputs connected to outside 0 to 5V signals > > to limit ingoing current > > That is recommended by MC in their circuit for taking /MCLR > low with a reset switch. Jason, do you use a reset switch and, > if so, does it take /MCLR direct to 0V ? The correct question is "is there a >100nF cap directly on the /MCLR pin?". The failure mode for which this series resistor is the cure is the Vdd dropping below /MCLR, which could cause the whole circuit to be powered from the cap via /MCLR, which is not a mode the PIC die is designed for. Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products docent Hogeschool van Utrecht: http://www.voti.nl/hvu