Power problems

[menta]

this is mostly hardware related, but maybe someone can help.

I'm using PIC16F877A as described in this circuit :
http://dj-gil.com/PIC/posts/SCHEMATIC4.pdf

When I use the programmer to power the circuit everything is ok.
But when I use the the 7805 to power the circuit I get junk on my LCD and nothing works.
Any ideas ?

BTW, the transformer is standard adjustable DC adaptor so it aleady has diode bridge inside.


Thanks.

[mackrackit]

BTW, the transformer is standard adjustable DC adaptor so it aleady has diode bridge inside.

What is the voltage out of the transformer?
May not be high enough.
What is the 7805 voltage when circuit is on (LCD)

[menta]

transformer output without load is ~16V.
7805 output is 4.95 while its on.

I have another circuit usining the same parts, with one change, I use the PIC Kit2 demo board with 16f887 which works ok.
When I use its 5V power for the second circuit I get the same results.

[gringobomba14]

Menta, 4.95V is good. Whats the current rating on the transformer? I can see maybe over an amp of current straight off without studying the schematic for longer than a few minutes. Perhaps there is just not enough current to power the LCD? Failing that, what is the current rating for your 7805? Depending on the package they're good for between 250mA and about 500mA. Try putting 2 in parallel (If the tranny has an output of greater than 1500mA)

[skimask]

In that schematic, I don't see anything connected to MCLR. If MCLR is floating, or worse grounded, the program might not get the chance to start.
Try adding a +5v line to the MCLR pin on the '887 and see what happens.
The program may already have the MCLR pin configured as an I/O, but we won't know without seeing the actual program itself.

Also, are you using an 887 or 877A? Because there is no 887A...

[menta]

Yes, its 16f877A, my mistake.
I tried connecting the MCLR pin to the +5v but it didn't help.
It also didn't help using 2x 7805.
Its very strange because I have another circuit just exact to this one but using a 887 on a demo board.
BTW, if I use the programmer voltage output (just + and - ) and connect them to the circuit its also working ok.

[menta]

From my first post

BTW, the transformer is a standard adjustable DC adaptor so it already has diode bridge inside.

I'm not using anything beside the PIC and the LCD.

[gringobomba14]

noise my friend, seems the only option at this stage.

[gringobomba14]

or your display is messed up. Checked the leads into the display?

Just out of curiosity, what is the rating on the tranny? and what was the total current draw on the circuit?

[skimask]

And once again, it sounds like it's time to go back to the drawing board with a 'blinky led'...
Yes I know it supposedly works fine on the '887 demo board, that's great.
Add an LED to the 877A board and get that working, then build back up to a clone of the 887 demo board.

[menta]

Guys,
Everything is working perfect when I use the programmer power.
A ~700 lines code.
The problem is very simple when connecting outside power source.

[mvs_sarma]

You are loading the 12V motor supply with regulator and on a 12V transformer.(16V~ on open circuit). when the motor is loaded, the transformer saturates probably and all the derived power supplies might go noisy.

Try to provide a separate supply for the 12V load. Things should improve.