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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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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.
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Lots of fingerprints...gotta clean those boards good before you etch. Pretty nice for a sharpie.Originally Posted by dragons_fire
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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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.
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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..
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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..
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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?
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