Atmega328 - Newbie design

Are you sure that your printer is printing at exactly 1:1 ratio - check the board overall dimensions to scale the printer.

MK

All were working earlier. now all of a sudden its happening. I've also re-installed eagle. Below is the dimensions in mm

So when you print it what does the 109.22 dimension actually measure with a ruler ?

MK

That's a horrible layout (in my opinion). Did an autorouter do it? If the primary of your transformer has mains on it, you need much better spacing there than the minimum default setting. The ground layout on the secondary side could be much better too. Having the output cap for the regulator up next to the switches at the top seems like an odd placement. You might also want to increase the widths of the tracks (for current handling ability) around the load switch and the snubber components. The isolation figure for the opto device controlling the triac is meaningless if you push tracks from the low voltage side between the pins on the high voltage side.

If you have to have a single-sided layout, perhaps consider a few wire links on the top rather than the very convoluted paths on the bottom layer.

Sorry if that sounds like a bit of a brutal critique. It's meant to be helpful (so you can improve the layout) rather than stop you in your tracks (so to speak).

Hi Jon!

Yes, that's a typical output from its auto-router. You soon recognise the 'style' of its output : )

Thanks guys for the feedback. Am just getting starting, taking those baby steps.

Figured the printout size, it was the generic driver that the printer had. Changed it to the recommended driver and all works well. Was gonna etch it today. Will hold it back.

You're absolutely right - I was just responding to the dimension issue and I didn't look at the circuit itself.

@George, Google "ipc mains clearances" - you'll get lots of hits which will give some idea as to what a board with mains on it should look like.  Before you do put mains on your own pcb do please post it here again - for more good, if tough, advice.

MK

Hi Jon,

Would you be having a documentation or provide me some tips to place the components. I have downloaded the autoplace_v3.ulp to see it can help but that returned an error "access open c:\windows\system32\place.scr". Any idea how i can resolve this.

Hi Jon,

Would you be having a documentation or provide me some tips to place the components. I have downloaded the autoplace_v3.ulp to see it can help but that returned an error "access open c:\windows\system32\place.scr". Any idea how i can resolve this.

So far I've got this from what I could gather reading. Maybe not best placement but would this be ok.

[I wrote this quickly before seeing your subsequent post, so this refers to your first layout.]

Sorry, I realise I didn't phrase that very well. I was referring to the track layout - the component placement isn't all that bad. Parts are mostly where they need to be with some exceptions. Remember I can't see your circuit and I'm reconstructing it in my head from the layout.

The capacitor on the output of the bridge rectifier needs to be right there at the output. Perhaps make it a 5mm pitch part (or bend the legs of a 2.5mm part to fit a 5mm placement).

It looks like the crystal and its load capacitors are on the wrong side of the processor. The tracks to the crystal should be short.

It doesn't look like there's a decoupling cap for the processor - certainly not one in the right place (next to the supply pin)

What are the resistors with the links doing? They don't seem to be pull-ups. Are they necessary?

Imagine a line 5mm wide drawn vertically up through the centre of the opto driver for the triac the full height of th eboard. Try and get all the mains stuff on one side and all the low voltage stuff on the other and nothing on the line. Think of it as a moat that nothing can cross except the transformer and opto driver acting as bridges. That gives you a reasonable minimum level of primary to secondary isolation on the board.

Move the PLED connector across so that it's not with the mains stuff.

I'd use a wider pin pitch than 2.54mm for the AC and LOAD connectors. 3.95(?) or 5.12 would be better.

On the mains side go for as much clearance as possible. You certainly don't want the situation where the tracks wind round the connectors with 0.15mm or 0.2mm spacing. The situation with the triac, where the track from the top pin slopes down and comes to within the minimum spacing of the centre, is out too.

To get a sensible track layout for something like this you need to do it by hand.

What is the fuse rating of the load circuit? That tells us the maximum continuous current and we can then tell you the minimum track width you'll need to carry it.

wow that was a mouth full . So to understand. I need to separate the mains AC from the dc side. GOT IT ! About the resistors, which one ? the AC mains is 240v with a 5amp fuse in it. The PCB transformer is rated at 9v 1.5VA. This is the below circuit.

I thought the devices down the board were selection links. They're LEDs, so of course you need the resistors.

To carry 5 amps, at 25C, on a board with 1oz copper, with no more than a 10C temperature rise you need a track width of something like 2.8mm (that applies whatever the voltage). However a fuse doesn't blow at the rated current (at least not quickly - look in a datasheet which will have a graph of time-to-blow against current), so you would do well to increase that to cover more than 5A. If you want to see how current varies with track width there are plenty of track width calculators online.

I can't go any further than this with the mains side. It's not something that I normally do and I'm not qualified to hand out advice as to how it should be done (I know what you shouldn't do, but I'm less clear on what you should do). In particular, I can't advise you on the clearances you need. I know it gets complicated, because it includes making judgements about factors like the environment the board will be in, and being careful to distinguish clearance (the distance through the air between two conductors) and creepage (the distance along a surface between two conductors) which may have different ratings.

Are you sure you really need to be doing the mains layout? Can you not do what you want to do with a PSU and a solid state relay?