I'll take that bet.Originally Posted by skimask
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.
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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.
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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!!!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.
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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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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I can not comment about the differences in the two chips.
Have you used this v-reg before? This is one part you may want to breadboard. I looked at the data sheet and did not see a minimum voltage, are you sure the batteries are charged. Try putting a known load on the v-reg and watch the output. Could be something wrong with the v-reg or cap size.
It still might be a good idea to build an adapter and bread board the PIC. Try another power supply.
Just looking back to basics. To many variables going straight to finished product.
Dave
Always wear safety glasses while programming.
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i just used my "power board" to power a 16f877A, the motor driver and both motors.. works good.. i would prefer to use teh 18f6585 because of # of I/O, memory size and speed..
i might just go back to using a 877A for now, just because i know i can work it..
i just dont know what else to do to get this 18f to work...
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You've got a 6 cell NiMH (or NiCad, doesn't really matter). Open circuit, they've probably got 1.3-1.4v per cell when fully charged. You put a load on them, they'll probably drop down to, say, 1.1v per cell, maybe less. As I stated earlier, with a regular linear regulator, you need a certain amount of 'voltage overhead' to keep the regulator working correctly...usually about 2 volts. Anything less and your regulator basically freaks and starts outputting a lot less voltage.
So, you've got that 6 cell pack, roughly 6.6v under a load, more likely less since you're driving motors (50mA no-load doesn't mean squat when you're trying to drive this thing around).
Looking at that datasheet you linked to earlier (Page 11, Figure 11), you need at least 6.1v @ 1.5amps of load to keep the regulator happy.
Try this for grins... lift the Treadbot up so it's wheels can free spin, power it up and see what your voltage is.
I'm thinking that you're going to have to run an 8 cell pack of AAA's instead of 6 AA's.
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well, right now my power board works great with a 16f877a, the motor driver and the motors. (both motors togetehr are around 200mA at full speed). when im playing with the 18f6585, i dont have the motors, motor driver and all the other little stuff isnt hooked up. just the pic and an led!!! when i measure the resistance across the board, (with the PIC in) i get about 1 Mohm. input voltage is around 7.4 (fully charged cells). but ohms law says that 5V going through 1Mohm, there is almost no current... not a short... even when i hook my multimeter up, it shows no current.. but the voltage drops right down to around 2V
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