pcb headache

W

wijnendael

New Member
This is my first post on the forum and hoping someone can give me some assistance with my problem.
I have made circuit for the PCF8574P and everything works ok when bread boarded and interfaced with the picaxe 18M2, however when i try the same circuit on a pcb that i designed in eagle the cct will not work. I have looked through it and find no difference between one and the other i have also tried a .1uf cap across the ic power pins but this also makes no difference can some tell me what is causing this, being new at this i am i am thinking it needs decoupling caps but where ?
 
Can you send your eagle files or .pdf of the board/sch?
More information will help.
 
I don't see a ground connection to R7-R9 on the pcb.
 
You need a capacitor from +5 to gnd close to IC1. A 0.1uf minimum. Maybe a 10uF and a 0.1uf.
I can't see the connection of R7-R9 but it must be there.
There is a yellow line from R1 back to the PIC on your layout. That indicates that the CAD program thinks the trace is not connected. It might be and it might not be.

I took paint and modified your layout to increase the size of ground and add a capacitor.
 
Thanks for the suggestion, i have made a few changes to schematic and pcb to incorporate your recommendations and will remake the board and see if it works. I don't etch the board but mill it on my cnc routerand therefore use pcb gcode to create my gcode file, below are a couple of images showing the pcb in eagle and also after pcb gcode has been run to show the milling pattern.
 
YES.
I tell people copper is free. Removing copper cost. (acid or milling time) Just leave all unused areas as ground or power.

You can try the capacitor on VCC to ground on the old board. Just solder it across the pins on the chip.

-----------edit--------
Did you put the copper in the top side or bottom side?
 
Although you probably don't need this, when view the PCB you can click the 'change' button, then 'package' and change the package of passives (resistors, caps and inductors) without having to change anything on the schematic. I often use this to change the pitch of TH resistors and caps, sometimes SMD, for easier layout.

I know you want a PCB, but the pinout of that device lends itself very well to stripboard, with the same pinout of your connectors.
 
The new board works a treat, however the old board also worked after having closer look one of the 4k7 pullup resisters had a dry joint on the +v when this was resolved the board functioned ok without the decoupling cap but it has been installed on the new one and the 10k address resistors have been removed and pins tied directly to gnd. Thanks everyone for the advise, all taken on board
 
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