It is based on a design I found elsewhere. I think it say it was for short protection or some such thing. But doesn't the LM317 already have that?

I will make the change at your recommendation.

They are only 10uf caps. Would they store that much of a charge?

See the National Semiconductor datasheet for the LM117/LM317, top left on page 9. Explanations are at the bottom of page 8 and top of page 9.

What drains the larger filter caps? That always seemed to be the bigger issue with this supply. The original designer suggested a permenent load.

They will eventually drain via the constant load of the regulators. Keep in mind that each regulator represents at least a 5mA load on the filter cap, depending on your "R1" values. The 7805 is approximately 5mA.

I think we've been over this before.

I will go ahead and add the center tap back in. One diode rectifier, just like before?

Yes.

 

Sorry do not understand. Do you mean it does not matter which way I go? If so I think I want to go with a separate board again. It will make a nice simple first PCB.

I was simply trying to say to cut your PCB a little bit bigger than you need for your design. If you try to make it exactly the size you need, it will make it that much harder to line up the mask properly. I didn't say anything about a 2nd board.

As far as the PIC part, leave that separate for now. No point over-complicating things. You can always use manual switches to test the thing out in the beginning, and add the PIC and voltmeter later.

Yes I know, I wanted to make sure I was doing it correctly in the small areas. Do they look ok? Just cover the whole board now?

Sure, it's OK. It's easier to just do the entire board in one swell foop. I haven't used ExpressPCB except for fiddling a bit, but in Cadsoft Eagle, you can lay out a polygon (copper pour) and give the polygon a signal name, like GND or VCC, and it will connect all of your GND/VCC nodes for you. This is handy when you are doing a two-or-more sided board.

OK I will fix those. But it creates problem for my DMM board but we can discuss that when the time comes.

I'm just saying to keep your pads/vias (you aren't using vias) out from the middle of a trace. Were you having the boards made by a production PCB house, it wouldn't be much of an issue. You CAN actually put pads/vias in a trace if need be, but it's best to avoid doing so whenever possible - and it's not like you are cramped for space.

If you were designing for production, you would want to cram things as tightly as possible; as each square inch costs money. If you had any wasted space, that would give your competition a cost advantage.

As far as clearance, that is why I had things spread out before. Maybe I got a bit too crazy trying to save space. I will spread things out a bit.

The only places you really might need extra space is around the regulators themselves (for heat sinks) and perhaps the capacitors, in case you can't get the exact size you originally specified.

I thought I got all of the pads in the middle of runs. Maybe I am not understanding. Is it one of the ones you marked above? Or are my traces going to the pads too big? Or do I need a longer trace to the component coming from the main trace?

o===o===o See that "o" in the middle of the trace on the left? Avoid doing that, whether the trace is straight, or curved. Any pad or via should be at the end of a trace, not in the middle of a trace.

BTW Thank you for using a blue pen and not a red pen, where you might risk lowering my self esteem.

I have my red pen and baseball bat handy, right here.

 

See the National Semiconductor datasheet for the LM117/LM317, top left on page 9. Explanations are at the bottom of page 8 and top of page 9.

Ahhhhhh. I see now. Should have given that datasheet another look. Making changes now.

They will eventually drain via the constant load of the regulators. Keep in mind that each regulator represents at least a 5mA load on the filter cap, depending on your "R1" values. The 7805 is approximately 5mA.

I think we've been over this before.

Sorry forgot.

Yes I know they drain eventually. Just takes a little while.

 

I was simply trying to say to cut your PCB a little bit bigger than you need for your design. If you try to make it exactly the size you need, it will make it that much harder to line up the mask properly. I didn't say anything about a 2nd board.

Understood. What I meant,should that extra piece be copper? Because I would have to mask it. Or just let that part etch off?

As far as the 2nd board, maybe I was not clear. It had nothing to do with cutting the board. I meant a 2nd board for my PIC power. I am still torn on that. One one hand one board is more efficient but on the other, it is a nice simple board. A good first time project.

As far as the PIC part, leave that separate for now. No point over-complicating things. You can always use manual switches to test the thing out in the beginning, and add the PIC and voltmeter later.

Yep wayyyyyyy ahead of you. Well this one time anyway.

o===o===o See that "o" in the middle of the trace on the left? Avoid doing that, whether the trace is straight, or curved. Any pad or via should be at the end of a trace, not in the middle of a trace.

Yeah I understand that. What I do not understand is where I am still doing this. I thought I got them all.

I have my red pen and baseball bat handy, right here.

Wow you know they outlawed corporal punishment some time ago?

 

Understood. What I meant,should that extra piece be copper? Because I would have to mask it. Or just let that part etch off?

I just etch it off.

As far as the 2nd board, maybe I was not clear. It had nothing to do with cutting the board. I meant a 2nd board for my PIC power. I am still torn on that. One one hand one board is more efficient but on the other, it is a nice simple board. A good first time project.

Make it separate.

Yeah I understand that. What I do not understand is where I am still doing this. I thought I got them all.

I got out the red pen.

The pads in the middle of traces are circled in red.

Possible clearance issues are circled in violet.

Not certain if you wanted it connected or isolated circled in yellow - either connect it, or give it more clearance.

 

Now you have gone and done it. My self esteem is now crushed. I am going to have to quit my job because I can no longer work. I will be a burden on society.


Seriously, thanks for your help! I see now what you mean. Thanks.

I pretty much have the whole thing redesigned and will post shortly.


But first I am submitting another design change. I got my hands on a couple of 16VDC wall warts. One is 2.2 amp the other 4.5 A. This way I don't have to buy that chack transformer. The downside is no center tap for my 5v supply.



1. Where would I place a fuse? (yes I know I should use a 1 amp fuse).

2. I know I need to eliminate the bridge. Should I still use my large filter caps? I know someone posted a wall wart psu and will look at that but wanted to get your opinion.

 

Now you have gone and done it. My self esteem is now crushed. I am going to have to quit my job because I can no longer work. I will be a burden on society.

Get back to work.

 

Get back to work.

Too late you used that red pen. The damage is done

Oh BTW I see BMorse recommends a bridge with a wall wart. It makes the supply more flexible. But you loose a volt or so. I think I will eliminate it.