Yes.
Now to clear uyp things... what would happen if the unused pin are set to output... and their initial state is high????
BTW once a PIC becomes hot... his lifetime is already reduced.. if it isn't already finished...
too bad
|
Yes.
Now to clear uyp things... what would happen if the unused pin are set to output... and their initial state is high????
BTW once a PIC becomes hot... his lifetime is already reduced.. if it isn't already finished...
too bad
Steve
It's not a bug, it's a random feature.
There's no problem, only learning opportunities.
|
Your board looks good for a first try or two. Your problem is like the others said “a short”. Are the stand-offs causing the trouble? Looks close in the picture. An exacto knife or insulator will fix it.
A few more things to keep in mind for the next one.
Traces should be no closer than 0.007 to each other 0.010 is better.
If VSS and VDD are next to each other, try to allow more, 0.010 may not be enough in the long run. Solder will grow “whiskers” over time and cause the gap to close. The more amps the more gap and wider the trace.
Clean all rosin from the board. Rosin will become conductive at elevated temperatures. Then use a sealer when finished testing. Spray lacquer works good to keep the air off.
Think of you board as a capacitor. Components and traces from top to bottom may have a capacitor effect. The large fields of copper that mister e spoke of will add to this problem. For fun you can build high voltage caps from pc board.
Most of all triple check your routing.
You will pick up more as you go.
Dave
Always wear safety glasses while programming.
|
come on guys, give me at least a little credit... all those shorts he pointed out have been scratched away, and tested with my multimeter..
i looked at it again quickly (while i was stopped at a red light), and i think the diode is the right way, but i did just notice i have a 470 ohm resistor instead of a 4.7kohm. could be part of the problem!!!stupid colour codes... too many different ones!!!
|
Easy now, we are not bashing you. Your problem sounds like a short. Sometimes this happens. I have been at this for a long time and just two weeks ago when all of the parts were stuck in the box things started just as you tell us yours is. Guess what. SHORT mashed a wire. Took a while to find it. replaced reg and chip. ..IT HAPPENS.Originally Posted by dragons_fire
I normally use a 470 from MCLR to VDD. I know this is not what is recommended but for some reason, can not remember, started doing it a few years back. So I would say that part is OK.
Take you board off of the machine and strip/unplug all you can. Add parts until you see smoke. If you have a box of chips
Like some one else said, look for somethin external that is hooked up causing the problem.
How are you driving the motors? Are the hooked up when the problem occurs?
Dave
Always wear safety glasses while programming.
|
i know no one is bashin me... im just jokin around a bit... when nothing is on the board, it works great, as soon as i add the PIC, i get problems. almost nothing is soldered to the board yet, just the essentials to get the pic running.. the reg, plcc socket, mclr stuff, the OSC and a header for ICSP...
i might go back to photoetching my boards, i just got a laser printer, so i thought i would give it a try for the toner transfer method.. this board came out ok for a first attempt at it, but it takes so long to get the paper off after its heated... i do like how i can see the design before i etch it, and if its not good, i just use a bit of acetone and start over... no transparencies (i dont have to go to staples to get them either), less nasty chemicals, ability to start over fairly easily and cheaper boards (because they arent presensitized.. i also dont have to worry about timing and stray light..
reading how others have done it, i used staples photo paper, and it took forever to get off the board. i tired using regular paper, and it seemed to work just as good, so i might experiment with it a bit more too...
it was a late night last night when i was soldering this stuff on... upon closerr inspection, im pretty sure it has to do with my MCLR stuff.. it looks like i might have confussed Vdd and Vss, so i think my resistor goes to ground when i think it should go to Vdd right??? im still in my van workin, so when i get home im going to check all the MCLR connections and make sure i got it right... but im almost positive thats where the problem is.. i cant see any shorts on the board, and everything works great without the PIC..
|
I just got back from a circuit card repair school, 7 weeks, got my Class 3 CCR Tech certificate. I got some serious training on the effects of 'tin whiskers' and old Rosin. Those 'tin whiskers' aren't nothing to play with. Got really good pictures of whiskers approaching 1/8" long after only a year on a PCB. And we took ohm readings across old, warmish rosin, and they were LOW...less than 1K in a lot of cases. Cool class though...
Far from it... I'm relatively impressed at the quality of that home-brew board.
Could you post a picture with and without the components? Might be a lot easier for us to help you troubleshoot this...upon closerr inspection, im pretty sure it has to do with my MCLR stuff.. it looks like i might have confussed Vdd and Vss, so i think my resistor goes to ground when i think it should go to Vdd right???
|
heres a couple pics of my boards:
first one, an old board from about 2 years ago, made with a sharpie marker.. PIC16F84A robot controller
second one, a board i made about 6 months ago using a presensitized board and on overhead transparency.... GPS interface for robot
third one, the one for this robot, using the toner transfer method...
|
here is a copy of the board layout im using for this thing, i have modified it a bit since i used it.. im not happy with this one that i made..
looking top down, blue is silkscreen, red is top and green is bottom copper layers.
top left 9-pin header is motor controller (wired properly, not installed yet), big thing in the top middle with 7-pin header is an SD card writer (not installed yet), top right labeled "tilt" is a memsic 2-axis accelerometer (not installed yet), 3-pin header in middle left is switch, right below the switch is the vreg, to the right is a 6-pin and 10-pin and 2 x 2-pin headers to go to top board (not made yet), OSC on right side of Socket, 10-pin header below socket goes to top board. LCD and my ultrasonic sensors arent installed yet..
|
What regulator are you using?
You said 5V @ 5A
The 5amp TO-220 ones I'm familiar with have Vout on the Tab.
It looks like your tab is connected to ground.
<br>
DT
|
My earlier statement about a 470 from MCLR to VDD is not quite correct for this chip. I have not used this one and after looking at the data sheet for it things are just a little different. VDD does go to MCLR but MCLR on this chip can also be used as an INPUT and has some different characteristics.
If I am looking at your board layout correctly, you may want to look at page 34 of the data sheet. I see MCLR going straight to VDD on your board. Do not know if this is the problem and I am getting a little fuzzy. Been up for 48hrs.
Dave
Always wear safety glasses while programming.
|
Lots of fingerprints...gotta clean those boards good before you etch. Pretty nice for a sharpie.
Lots of extra flux, but no fingerprints I can see. And again, pretty good. 90 degree corners aren't the best though once you start dealing with higher frequencies.second one, a board i made about 6 months ago using a presensitized board and on overhead transparency.... GPS interface for robot
Get some rubbing alcohol and those soft acid brushes ( http://www.tecratools.com/pages/asso...ics/15215l.gif ) to break down and clean off the excess flux when you're done soldering. That stuff will harden up over time and eat away at everything, as well as possibly cause high resistance shorts (low resistance opens?third one, the one for this robot, using the toner transfer method...
|
youre right, the vreg im using has an output on the tab. so thats been fixed now, but i still dont think that was part of my probelm, since everything works when the pic isnt in it..
i tired taking out all the MCLR stuff so it doesnt connect to anything, and it still heats up pretty quickly.. im starting to wonder if the chip is destroyed and that causing it to heat up now, or if there is still something wrong..
in the schematic, MCLR is connected through the diode to the resistor and cap. its also connected to the prog pin. i see where you thought it connected to Vdd, but it actually doesnt.. the data sheet i have, its a notes page on page 34. page 35 has stuff about resets and shows the same wiring that i have.
when i etched this board, there is copper on the top too, and some of my pins dont match up perfectly, so there could be a short under the socket. i checked before i soldered, but i could have missed something..
im going to play around with the toner transfer, and see if i can get it any better. if not, i will probably make a new photoetched board.
so changes to the board now are:
vreg tab connected to output,
no more ground planes
MCLR stuff layed out better,
copper pads on top are gone, (except for the top traces)
.01 gap between pads and traces, .02 betweeen traces
more gap between Vdd and standoffs (Vss)
thanks for the comments on the old boards i made.. when i started, i thought the sharpie was the only way to do it, and that it needed sprecial equipment to make boards any other way. the photoetched one, was actually something called RCAP, its an autopilot for RC planes. its an opensource project, and the board layout was straight out of their website. it runs at 2400 baud, so i dont think it will have too many problems with 90 degree corners.
but i will stop typing now and go play with my toner and see what i can do..
|
All of the MCLR stuff? resistor and all?
Chip destroyed - entirely possible it's shorted internally...
I wouldn't throw that board out just yet. There's plenty you can do with an exacto knife, fix-it-jumper-wires, and a soldering gun.when i etched this board, there is copper on the top too, and some of my pins dont match up perfectly, so there could be a short under the socket. i checked before i soldered, but i could have missed something..
Nothing wrong with ground planes, as long as they're connected to ground! It's the unconnected ones that may cause trouble. Also, a big slab of copper under a part also makes an effective heat sink, whether it's connected to ground or not. Good calls on the rest of the notes...so changes to the board now are:
vreg tab connected to output,
no more ground planes
MCLR stuff layed out better,
copper pads on top are gone, (except for the top traces)
.01 gap between pads and traces, .02 betweeen traces
more gap between Vdd and standoffs (Vss)
It's not the communications at 2400 baud that you'll have trouble with, it's those signals running at 10mhz+ hitting that 90 angle, causing a reflection, that reflection bouncing back on it's input and possibly pulling an input back low somewhere else, or something this or something that.it runs at 2400 baud, so i dont think it will have too many problems with 90 degree corners.
Don't forget, just because your PIC is only running 10mhz or whatever, each edge of each signal (square wave) is a small chunk of a wave of a much higher frequency (depending on how fast it rises and falls). The higher the frequency, the worse the problems. Suffice to say, 90 bad, 45 good enough, at least it's worked for me up to about 80mhz.
|
i needed a little sense of accomplishment, so here it is!! it running off of an 877A with a pololu micro dual serial motor driver..
|
heres the .PCB file (PCBexpress) of my board as it is right now.. if anyone is bored and wants to take a look and see if they can see anything wrong, let me know...
if you have any suggestions on how to make it better, those would be appreciated too..
i think im going to remake the board.. i like making them, its half the fun..
i had to ZIP it or else it wouldnt let me upload it...
thanks for all the help guys.. i like playing with this stuff until i can get it to work... but this time its getting a little frustrating because i cant really seem to find the problem..
|
A lot of people, myself included, would be more than happy to have a look-see.
Could ya dump the file as a pdf or some sort of 'standard' file besides that PCBExpress file?
|
Skimask- PCB Express is free and a small download, turn layers on and off, nice program.
Dragonfire- by chance have you breadborded this this yet, at least the parts giving trouble? Looking at your layout now.
Dave
Always wear safety glasses while programming.
|
well, i was thinking about a pdf, but the reason i left it as a PCB is that it will still have the layers... but here it is as a jpg
i think i will attempt a new board, i just wanna make sure everything is good before i do it...
did you watch the video???
|
Video is good. When it is finished it would make a good kit.
Dave
Always wear safety glasses while programming.
|
Again, I have not used this chip.
The trace I mentioned before was the program trace. But I still think the MCLR part is different than the data sheet, data shows diode going VSS?
Other than that and a few sharp turns, I do not see a problem.
The sharp turn thing also give a real nice place for arcs to show up.
Whats the law? Things in motion want to keep going in the same direction? Even electrons.
Dave
Always wear safety glasses while programming.
|
im at work now, but i will have a look at the MCLR diode when i get home... like i said, im just going by what the nuts and volts says for ICSP, it may be wrong for this chip.. and thats exactly why i appreciate youre help... because i have never used this chip before either, so im learning lots as i go..
about breadboarding, is there an easy way to put a PLCC on a breadboard?? without making a board with a header than can be plugged into the breadboard???
when you said "kit" i dont know if you meant selling it, cause im just doing this fur fun, but i guess anything is possible...
i will look at the sharp corners... i know they arent good, but i didnt think it was as big of a deal as it seems....
|
If I had a dollar for every one of those magazine articles I've seen that was obviously wrong (well, I'd have about 10 bucks, but the point remains the same).
It's not as big of a deal as we're making it out to be....but again, it could kick you in the arse in the future...i will look at the sharp corners... i know they arent good, but i didnt think it was as big of a deal as it seems....
P.S. Watched the video...pretty neat stuff...
|
i just remembered that the MCLR schematic is also in the stuff that came with my programmer... i should look there too!!!
if i had a dollar for everytime something is going to come back and kick my in the arse, i would be rich!! (at least until i die from the viscious arse kickins!!!)
thanks for the comments on the video. the controller does 128 speeds, so i made it ramp up from 0 to 127 with a pause 20 between each step..
i also get an unbelievable amount of noise when the motors are running.. with both going full speed, i cant even make out the picture on my tv. i think i may need to add some caps to the motors..
|
Cap's across the motor may help, but it's probably the result of the frequency of your PWM. What is the freq anyways? Maybe we can help you come up with something a bit higher so you can't hear it (but your dog will go nuts!!!).
Last edited by skimask; - 17th April 2007 at 23:07.
|
could be from the PWM, im using a serial motor driver, to keep things simple.. so i cant "easily" change the freq. its not the "hearing" noise im worried about, its the static (snow) on the tv. im just worried that it may affect my circuit since the motors are only going to be an inch from the board..
|
The noise showing up on the tv shouldn't affect the motors (ever noticed when you run a blender in the kitchen that the tv in the living room goes nuts?).
Can you 'scope the PWM to the motors or put a meter with a freq reading on it?
Any reason why you're using serial motor drivers? Other than it's already done and one less thing to worry about...which is handy...
And I just thought of something. You said the gear ratio is something like 298:1. All that noise is probably just regular motor noise. How do the motors sound on straight DC battery type power?
Which reminds me...where did you get the tracks? I've been wanting to build another R/C lawnmower and want to drive it with tracks instead of tires...
|
im using them because they are already done... all i need to do is output a serial command, and the motors drive...
example command:
serout2 motor, motorbaud,[$80,0,lfwd,speed]
$80,0 are commands for the driver. lfwd is left forward. and speed is one of 128 speeds
i send one command and the motor driver keeps it at that speed until i tell it to change.. lots less for the PIC to worry about..
im jsut worried about the "electronic" noise affecting the PIC and other stuff on the board...
my tracks are probably a little small for you... the "tiles" on the floor are 6 inches across, so my tracks are tiny... they came from a tamiya dozer kit, it was the leftover track parts. each side has 3 pieces of track connected together...
when i get home, i will upload a picture of the tracks on one of my other toys... they would be almost perfect for a lawnmower, except that they would rip up all the grass!!!!
|
heres pictures of my tracks on my bigger robot... (its not really a robot yet, its controlled my RC right now... ) theres a 9v battery on top for a size reference...
this link is for the programmer im using.. its wired almost the same as mine, except they dont have the cap.
http://www.melabs.com/images/icsp1.gif
reading about what they say about ICSP, i need to modify my board some more.. it looks as though i need to connect AVdd and AVss too, and it says i need to pull PGM low with a 100k resistor. i also forgot a cap across the vreg.
|
You're right on everything you mentioned so far. AVdd and AVss NEED to be tied to Vdd and Vss during programming only. During normal ops, they can be seperated. And pulling PGM low is a good idea (in my mind) whether you are using HV-ICSP or LV-ICSP, maybe throw a jumper in there or something for future 'optionability'.
And put .1uf cap's across every chip, every Vdd/Vss pair, heck throw a couple extra in there when a power or ground trace runs for a few inches without one, if you've got the room for it whether you actually plug one in or not. It'll save you future headaches and give you extra spots to pull a power or a ground.
Since you are wanting to redo your boards, you might want this hint...
For a couple of years now, every time I design a board, I put extra via's on every trace/signal/line/whatever, whether I actually use them or not. Doesn't matter where I put them, I just put them wherever they can fit, and they don't have to be double-sided via's. This way I leave myself a load of future re-config options. I can cut a trace here or there and install jumper wires if I want (or more likely, fix a screw up!
And those tracks...that's a good idea. I didn't think of putting cleats on chains like that. How well do the chains track over the sprocket when the bolt heads hit the teeth on the sprockets?
Motor drivers - can't argue with that...
|
my problem with this board, is that i rushed into it, without fully thinking things through, and doing my research.. now that i have done some research, snd thought about this board more, i feel more confident that its going to work.. im also going to omit the pads in the top that arent being used (pcbexpress automatically makes pads on the top and bottom of holes). i have been thinking about the 90 degree angles all evening (ive been installing IPTV all evening, and even using staples that hold the wires snug can destroy the signal.. wires need to have a certain radius for each corner, and cant be kinked...) so i angled some traces so they have 45 degree bends now..
i will upload another copy of the board later, to see what people think..
if you look closely to the sprockets, some teeth are actually cut out to make clearance for the bolt heads. imworking on changing that design too. i think im going to use only one chain for drive, and make some kind of wheel to support the otehr side. the chains dont stay on well now, because it was almost impossible to make both sprockets line up perfectly... i also want to say, its driven by 2 windshield wiper motors, with 3 x 8.5A 12V sealed Gell cells. one for each motor, and one for the headlights.. we have lots of old coal mines and caves around, so its meant to be able to explore them...
|
Maybe spot weld those cleats to the top of the chain links?
And the bigger bot---do I see one (or more) of those cheap Walmart wireless camera's (one of those that transmit direct to channel 3) on your shopping list? I've got one of those...works pretty good with crappy antenna's out to about 200ft with a bit of overvoltage at the TX (11.1v vs 9v, 12v w/3 diodes in series).
|
never seen wireless cams at walmart.. gonna have to go tomorrow... i already have some wireless cams though, and one of them is a lot more powerful than most of the "consumer" ones.. its great havin a "ham" license...
i tried welding the cleats to the chain, but it wrecked the "bearings" in it, and so the chain couldnt "flex" very well. the bolts work great, i used to have 3/4" ones on every second cleat, and there was no way it would slide then. it had some trouble turning though because of it, and it scratched the driveway pretty good.
so do ineed the cap in on the MCLR to ground? or should i just leave it in??
my chip has a max speed of 40mhz but all i have is 20mhz resonators. most equipment on the board is meant to use serial commands at 2400 to 9600 baud. i would also like to experiment with some mapping. would it be worth it for me to run it higher than 20mhz, or do you think it will be fine?
|
An adapter is the only way I know to board a PLCC making one should be easy or http://www.arieselec.com/products/18014.pdf
Yes, selling it. Looks like something that would get some interest.
BIG BOT looks like a better snow plow than lawn mower
I think 20 mHz will work, as you say, the motor drivers free up the PIC.
So your a fellow HAM north of the line, cool.
Dave
Always wear safety glasses while programming.
|
They're really cheap cams. Resolution isn't all that good, color's a bit off, but they work.
Welding - I didn't think of that. The pins on those chains are probably pretty cheap metal anyways.
MCLR cap - usually, it's there to keep MCLR held off for a split second during power up. The built-in power up timer handles that for 72ms if enabled. And the cap will also help with keeping transient power flux's from tripping MCLR.
40mhz vs. 20mhz - If you've got anything 5-10mhz laying around, try enabling the internal 4XPLL. The board should run at 40mhz, especially since you aren't trying to interface with anything major like static ram or whatever...yet...
|
i actaully thought about it, there the backup cams arent they?? i have seen them...
we have a wonderful store here called "princess auto", its a surplus store. sprockets were a dollar each, chains were $8 for 6 feet.
it was actually designed as a snow plow, not a lawnmower. we have a driveway big enough for about 6 cars, and its a real pain to shovel it. at no load, the motors run at about 1.4amps each, and when im sitting on it, riding around, it runs at about 3.5 amps each. in a couple minutes, i will upload the new board design, and see what you guys think, then maybe i will make a new one..
|
heres the board as it is now.. rught below the tilt sensor, i have a resistor, its supposed to be a cap, i just put the wrong symbol, so that has already been fixed..
let me know if you see anything wrong, i will probably start making it soon.. or if you have any opinions on what i should do differently.
|
Nothing wrong that I can, but I think I would make another +5v line run from your regulator up the left side of the board to make a complete loop instead of a half a loop. The way you've got it right now, whatever is at the 'end' of your 5v run will probably pick up a lot of noise, and if it draws any sort of load, it'll really put spikes on the run going back towards the PIC. Might mess it up.
Maybe a 'sprinkling' of .1uf cap's across +5v and ground here and there, if you can fit an extras in there, might not be a bad idea, even if they're surface mount and you have to solder them across the traces themselves. I've done that a few times just as a precaution, used 0805 sized, just laid them right there, no marking or anythiing, just added them in...
And I think it looks much better without all those 90 degree angles in there...
|
I knew it! Been 20 years since I have seen snow, BIG BOT brings back memories.
The board looks good. Agree with Skimask about the VDD trace, if you do not have room put the caps at the end of the run.
Dave
Always wear safety glasses while programming.
|
Want me to send you some snow?
|
i think it looks better too without the 90 degree angles.
i added a complete loop around for the power. the thing at the end, was the motor driver. it uses battery voltage for the motors, and 5V for the components on the board..
i also added 2 more caps around the board.
Members who have read this thread : 0You do not have permission to view the list of names.
Posting Permissions
Bookmarks