Electronics > Electronics

Need quick PIC help

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jsmoker:
I found a "solution" but I still want to know why this happens if anyone can tell me.

I found that by adding a capacitor >30uF between the voltage regulator and the PIC rather than where I tried before between the power source and voltage regulator, things work fine.  Why is the capacitor necessary?  Why do I need so much capacitence.  I still get a start up delay when I use like 10uF.

-JSmoker

Admin:
what is your power supply? a battery? it sounds like you have a very low current problem . . .


the regulator issue seems odd, cause you need at least 6V input for a voltage regulator to output 5V (there is like a 1V dropout) . . .

as for the capacitor, its better design for it to be between the regulator and PIC . . .

i have no idea what is causing your problem . . . do you have a schematic you can upload?

jsmoker:
I tried both battery and power supply, but mostly I was relying on a power supply.  The batteries I tried were a 7.4V Lithium Polymer and a Alkaline 9V. And there's also the 5V from the programmer that worked.  I can post the PCB Layout that I'm using. But I'm not sure how to use the "Image" option.   The layout might look a bit complex, but when I did the above tests, I only had one LED which is on the corner of the board out from Portb3,3 switches, the two 8 pin SOICs and voltage regulators.  The switches you can consider shorted, and the SOICs aren't doing anything right now.



-JSmoker

Admin:
hook your circuit up to a power supply and let me know what the current draw is. it should be under 50mA (with the LED on) . . .

also, get out a multimeter and check various pins across your circuit for anything unusual (if you haven't already). also, do a resistivity check on connections that are close to each other and make sure nothing is shorting.

to upload schematic:
there is a text link that will say 'Additional Options...' towards the bottom of a reply post.
it will bring down a drop down menu that allows you to post attachments. schematics save best in the .png format for good image compression.

the other method is to use the image button. you put the image on your server, and just link to it.

jsmoker:
The current is actually around 100mA and I've found this to be true for other models I've built,  I think due to the fact that I'm using the PLL option.  I've read several times that running a chip at it's greatest speed draws a lot of current.  I'm not positive, but I think the PLL might also be the source of my start up issues.  I just wish I knew what the details are so I can make sure I prevent this in the future.

-JSmoker

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