555 Timer educational kit board

[Dariusrussell]

Hey, I have all the info needed on my project at , blinkyboard.blogspot.com
Anyway, could someone with good pcb engineering experience tell me if all my connections check out, and if just the board checks out in general?

[c4757p]

I haven't gone through every little bit of it, but a few things jump out at me:

1) What's with the extra holes between the resistors?
2) Your routing will be much nicer if you pick perpendicular directions for the two sides of the board - horizontal traces on top and vertical on the bottom, for example.
2b) If you need double-sided for a 555 circuit you should rearrange your components. This circuit can be done neatly with one layer and no jumpers, with a little work. For an educational circuit it might be helpful to have all the traces nicely visible on top (omit a ground plane - or put it on the bottom) so people can follow them.
3) If this is supposed to be educational in some way, perhaps the arrangement with the 555 at the bottom and all the components dumped in a row at the top isn't the best? You might want to make it more obvious how they connect by putting them closer.
4) "Rev 25"? 

[dr_p]

1) What's with the extra holes between the resistors?
[...]
3) If this is supposed to be educational in some way, perhaps the arrangement with the 555 at the bottom and all the components dumped in a row at the top isn't the best? You might want to make it more obvious how they connect by putting them closer.

I think he's planning on using sockets for the IC and other components, so that's a DIL18 socket.

[c4757p]

No, it's not, it's spaced at 400mil.

Edit: But obviously it could be two SIL headers. --- If you're going to socket everything, why not just use breadboards??

[AndyC_772]

What do the students actually learn by plugging in the components - other than that trying to plug in bent components which other classes have already used is tricky?

It seems like an odd project to me. If they're meant to be building something for themselves, give them breadboards and a guide to what they should plug in where. That's quite a useful skill and worth teaching, IMHO.

Alternatively, if the object of the exercise is to analyse the 555 timer circuit itself, then maybe it makes sense to have a pre-assembled circuit which students can probe. Such a board would be robust, re-usable, and guaranteed to have been built correctly. In that case, having the components plug in is a waste of time, just solder them and be done.

[Dariusrussell]

Ok well this is for a school and getting soldering irons for every class is a bit difficult, and yes they are supposed to analyze the 555 timer and how it works. I double checked to see if the spacing is 400 mil, its at .1 inch. I might try what c4757p said and just have each component socketed on its own. Thanks for the advice.

[c4757p]

I meant the space between the rows - that is 400 mils. If you wanted to use a DIL socket it should be 300 mils for a narrow socket or 600 mils for wide. Your column spacing is correct at 100 mils. I'd prefer a wide DIL socket (600 mil) for socketing axial components.

This being for a school, I think you should just use plain breadboards. In fact, I personally think that the students should be presented with a block diagram of the 555 and have to figure out for themselves how to make it work. It's a very simple chip and plugging shit in doesn't do much to help them.

Especially don't give them the PCB traces. There's a lot you can do with a 555 if you deviate from the usual circuits that enterprising students will be able to figure out.

[Dariusrussell]

Hey thats a great idea, I might go with a DIP socket, but I will defiantly consider a breadboard too. I did get a single sided board layout too.
At this point it all depends on the cost because of school budgets.
Anyway thanks for all the help and suggestions!
Darius