Criticism on pcb routing and advice re pull up resistors

adegnes: Heres a version with capacitive coupling of the ignition signal between the board layers before it enters the circuit. I also moved stuff around a bit. What do you think?

Move the TMP 36 and its associated cap a couple of mm to the right to remove the kink from the connection to A2. Connect the 5V trace horizontally from the cap to the 5V line and remove the diagonal 5V trace from the TMP 36. Draw the 5V trace from the 1uF cap by the 3 pin connector horizontally to pin 4 of the 555. You may need to move the cap down a fraction to get it to line up. Also change the right angle connection of its 5v trace to a 45 degree one, pointing towards the connector. Draw a trace from the positive end of the 18K resistor vertically, under the bridge, to connect with the sloping 5V trace near the 5V pin. Remove any unnecessary traces.

Thanks. Here's the new version.

Oops, forgot the picture…

Found another stupid mistake; had the bc547 connected to pin 6 and 7 via the 18k, was supposed to go to pin 2 via the 10k… Can’t believe I missed that one!

That's looking neater. The 5V rail is still a little unconventional with all those branches. Look at other PCBs, you don't see wires branching like that.

The reason is that every corner or intersection in the trace acts like a reflector to certain (high) frequencies. The more reflections, the more noise. This is usually only a problem for high speed data circuits but that high speed data has to come from a power wire somewhere, so there will be high speed current pulses on the power wires.

The more normal layout is to wire to the components and branch off from the component holes. The corner that the current makes going up the component leg is an unavoidable reflector, so try not to add any more.

For this project, it doesn't matter, since you're not working with those frequencies. But keep it in mind for your next project.

adegnes: Oops, forgot the picture...

Found another stupid mistake; had the bc547 connected to pin 6 and 7 via the 18k, was supposed to go to pin 2 via the 10k... Can't believe I missed that one!

A little better, but you didn't connect pin 4 of the 555 horizontally to the 1uF cap 5V. You went round the houses! When you've done that, the trace then goes from pin 4 of the 555 to 10K, from the 10K to the 18K and from the 18K [u]straight[/u] up until it joins the 5V line near to the 100nF cap. That will get rid of one track join. When you've done that, I'll tell you how to get rid of the other two.

MorganS:
That’s looking neater. The 5V rail is still a little unconventional with all those branches. Look at other PCBs, you don’t see wires branching like that.

The reason is that every corner or intersection in the trace acts like a reflector to certain (high) frequencies. The more reflections, the more noise. This is usually only a problem for high speed data circuits but that high speed data has to come from a power wire somewhere, so there will be high speed current pulses on the power wires.

The more normal layout is to wire to the components and branch off from the component holes. The corner that the current makes going up the component leg is an unavoidable reflector, so try not to add any more.

For this project, it doesn’t matter, since you’re not working with those frequencies. But keep it in mind for your next project.

Thanks for explaining.

Henry_Best:
A little better, but you didn’t connect pin 4 of the 555 horizontally to the 1uF cap 5V. You went round the houses!
When you’ve done that, the trace then goes from pin 4 of the 555 to 10K, from the 10K to the 18K and from the 18K straight up until it joins the 5V line near to the 100nF cap.
That will get rid of one track join. When you’ve done that, I’ll tell you how to get rid of the other two.

Ok, I must have misunderstood you.

I rearranged things a bit, here’s what it looks like now.

You must admit, there is quite a difference from the first version. ;)

Yep. You should have seen the real first version, what I posted was maybe version 10 or something...

Thanks for all the help!

You could add pads from A2 to GND to accommodate a 10K resistor and a capacitor. If they are not needed, don't populate.

What is the diameter of the resistor pads, these could be bigger, even 80 mil is reasonable?

adegnes: Yep. You should have seen the real first version, what I posted was maybe version 10 or something...

Thanks for all the help!

Yes, much, much better.