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1.036kohm across vdd and vss "with" and "without" the chip. i tried another regulator that isnt mounted to anything, and it comes back with the same reading.Originally Posted by skimask
5V without chip, 4.48V with chip
when i put my meter on the doide symbol (i have never used it before and dont know what it is), i get .324V without any power applied to the board (im assuming there isnt supposed to be)
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1-ish Kohm... hmmmm...no dead shorts. Something is turned on by the PIC.
Something's loading it down! Try disconnecting the motors? Try disconnecting and unsoldering stuff until you find the 'leak'. Maybe change your program a bit to make absolutely sure nothing is being driven for X seconds before something starts to happen.?.?5V without chip, 4.48V with chip
Try this with the 'diode' symbol on the meter. Hook the meter up to a plain ol' diode, 1N4148, whatever you've got handy. Whatever the meter reads (within range of course) is what the forward voltage drop of the diode is and if the meter leads are connected correctly. The datasheets on the diode will tell you what the nominal values are. You can also use this function to correctly identify leads on a transistor.when i put my meter on the doide symbol (i have never used it before and dont know what it is), i get .324V without any power applied to the board (im assuming there isnt supposed to be)
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to be honest, when i said everything was soldered to the board, i really meant there a couple things soldered to the board... right now it has the regulator, the PIC, OSC, power switch, headers and i have a diode, resistor and cap on the MCLR pin.. they are connected exactly the way it says too in the march 2007 nuts and volts... mclr goes to the programmer, then there is a diode off of that, with a 4.7kohm resistor to dvv, and a 1uF cap to ground.
it gets so hot so quick, that i havent programmed anything into the pic yet, and because its a plcc, i cant really use my breadboard to try it...
im heading to work though, so if i get a chance, i may look at it some more to see if i can find any shorts on any pins, and make sure i have the mclr stuff on right..
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I'll put money on the MCLR diode put in backwards.
Any takers for odds?
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i'll bet on at least one I/O short to GND (Vss) or short to another I/O. Try to set all unused I/O to input. But before, remove the PIC, measure impedance between ALL i/o and Vss, then Vdd.
Something suck juice here...
OR, a VSS is connected to VDD and so on... kind of routing mistake
If the MCLR pin was just put backward... the PIC would just act oddly... not suck as this juice.
How about the current measure?
Last edited by mister_e; - 16th April 2007 at 22:43.
Steve
It's not a bug, it's a random feature.
There's no problem, only learning opportunities.
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I'll take that bet.I'll put money on the MCLR diode put in backwards.
Any takers for odds?
It's got to be the Plethora of shorts that mister_e pointed out in the picture.
<br>
DT
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But the poster did say that the regulator/etc didn't get hot until he put the PIC in the socket. Doesn't really make sense to me either. Maybe the stress across a couple of pins on that socket are shorting out only when the chip is in.
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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.
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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.
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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!!!
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i just realized that im using a PIC18LF6585, not an 18F6585. from what i have read in the dtasheet, the only difference is that the LF will work at lower voltages, but i think it will still work at 5V.. does anyone know if thats true or not?? if its not meant to run at 5V, then that would explain my problem...
i dont get any heat now, but it pulls my voltage down to about 2V when the PIC is in it...
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