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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!!!
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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.
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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..
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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???
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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...
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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..
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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
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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...
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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..
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