Power problems

[menta]

Its amazing,
When I use the test board (http://dj-gil.com/PIC/posts/math.jpg) everything is ok.
When I put in the wireWrap board (http://dj-gil.com/PIC/posts/WW1.jpg)
(http://dj-gil.com/PIC/posts/WW2.jpg) its not working.

[skimask]

Its amazing,
When I use the test board (http://dj-gil.com/PIC/posts/math.jpg) everything is ok.
When I put in the wireWrap board (http://dj-gil.com/PIC/posts/WW1.jpg)
(http://dj-gil.com/PIC/posts/WW2.jpg) its not working.

Just because it works on the 'test board' and it doesn't work on the 'wirewrap board', doesn't mean you schematic/parts are correct for that particular application.
I don't see any capacitors across Vdd/Vss on the 'test board', but that doesn't mean there aren't any there (i.e. stray capacitance).
I see a single resistor leading over to MCLR, but no capacitor, again, doesn't mean there isn't any capacitance on MCLR (albiet stray caps). And it also doesn't specifically mean that you have to have a capacitor across MCLR to ground, but it sure doesn't hurt.
It also doesn't mean that your wiring, no matter how many times you've checked it, is correct and without fault.
It also doesn't mean that the program you wrote for your '877 is actually going to run on your '887, or the other way around, without any changes in the source at all. the 16F877A is an old chip, the 16F887 is a new chip. A lot of differences between the 2.
Maybe your programmer's power supply is a lot smoother than the other power supply you're using.
Maybe your other power supply can't handle the extra load and dumps causing a reset, maybe it doesn't come up fast enough to satisfy the PIC, maybe it comes up too fast.
1650 different reasons why stuff don't work. I think we've isolated like 3 possibilities...

[menta]

I think i'm not going to use the 877A.
Too much trouble comparing to the 887.
I spent 2 days on this issue and I still can't understand why it works or not.
Thanks.

[menta]

btw, I've reached a point where my WW board is working, only when I use LONG wires to the external crystal.
I guess this cause some kind of induction which makes it do work.
I was using a very expensive wire (some kind of wire used in plans, teflon isolation, non melting) and it didn't work. Only when I used some simple 26 AWG wire it is working.
go figure.

[Archangel]

btw, I've reached a point where my WW board is working, only when I use LONG wires to the external crystal.
I guess this cause some kind of induction which makes it do work.
I was using a very expensive wire (some kind of wire used in plans, teflon isolation, non melting) and it didn't work. Only when I used some simple 26 AWG wire it is working.
go figure.

Hi Menta,
every piece of wire, every component, every circuit board trace, exibits properties of both capacitance and inductance ( which means they act to some degree as both a capacitor and a coil ). The Oscillator in the PIC requires just a certain amount of each, or it will not work. When you use a crystal, you must use the correct value capacitors in the circuit or again, it will not work.<br>
That said, imagine the long wires running parallel to one another. every mm of that wire adds capacitance to the circuit, probably why it works with the long wires and not the short ones. One big however is, the long wires also work as coils and will throw off the frequency of the Oscillator. So as Skimask pointed out, put in the capacitors, on very short wires and enjoy your success.

[skimask]

btw, I've reached a point where my WW board is working, only when I use LONG wires to the external crystal.
I guess this cause some kind of induction which makes it do work.
I was using a very expensive wire (some kind of wire used in plans, teflon isolation, non melting) and it didn't work. Only when I used some simple 26 AWG wire it is working.
go figure.

Are you using any cap's on your crystal at all?
In fact, are there any capacitors anywhere on your circuit board?

[menta]

At first I used capacitors on each device just like the book.
Crystal to PIC with 2x 22pF cap.
Did everything nice smooth and easy. All looked very good.
The whole problem was due to that 2 wires to the Cystal.
Thanks.

[gringobomba14]

Morning Menta,

The 877A is a bit tempremental at times. I use it for a lot of projects, and I find that some times it works under strange conditions when it shouldn't. We've established that you have a resistor between VDD and MCLR, try wiring the MCLR direct to the 5V line. You will need 18pF or 22pF caps on that crystal. Back to super short leads and the caps between the xtal and ground on both sides. It's not just because we say it, it's because thats how they work.....
Your transformer (I noticed you never answered what the rating is/was) probably has a lot of noise on it, so try putting a 470uF cap accross the output of the tranny and if possible, accross the output of the 7805. That will smooth out any ripples that may be around. Just because it SAYS it has a complete DC output doesn't mean it's true.
Hope that helps some