from Eagle Schematic to Board problems... rules of thumb? Advice? Help?

Hi All

I am working on building a small pcb for a 3 band guitar eq. I am using the schematic of someone from a guitar forum, the Phabbtone EQ. I have adjusted his schematic a bit, and I have put the schematic in Eagle. But then it takes me ages to turn it into a board in Eagle. At one point, I had a nice layout, and after that, the making the actual pcb with photosensitive boards and a light unit is pretty easy. But I had made a mistake and now it is taking me hours again to get it into a board. Are there any rules of thumbs or guidelines to make this process a bit easier? Or is it just a matter of keeping on trying?

Cheers

Erik

PS this is the schematic, not that difficult I would say:

erikb1971 said:

...I have adjusted his schematic a bit, and I have put the schematic in Eagle.

Click to expand...

Maybe adjust it again to get it working at all. (Connect the neg.supply rail to opamp pin-4 instead of IC1A's feedback loop).
The schematic better would have pots (with parts value and type of taper) connected, so you'd have a better chance to revisit or fix it some day.
Trim1/2+3 without a resistor in parallel might wake up the neighbours when the trimmer fails one day, causing this gain stage running open loop. Trimming R7 instead will give less annoying results in case of parts failure.

But then it takes me ages to turn it into a board in Eagle. At one point, I had a nice layout, and after that, the making the actual pcb with photosensitive boards and a light unit is pretty easy. But I had made a mistake and now it is taking me hours again to get it into a board. Are there any rules of thumbs or guidelines to make this process a bit easier? Or is it just a matter of keeping on trying?

Click to expand...

Keep on trying. Every iteration process will probably get you to a better layout than the 1st try, but maybe only a [ripup] of the wrong routed traces already gets you there, so you don't have to start from scratch. Just remember to have both files (schematic and board) open while editing, else the result will be inconsistent.

Harpo said:

erikb1971 said:

...I have adjusted his schematic a bit, and I have put the schematic in Eagle.

Click to expand...

Maybe adjust it again to get it working at all. (Connect the neg.supply rail to opamp pin-4 instead of IC1A's feedback loop).
The schematic better would have pots (with parts value and type of taper) connected, so you'd have a better chance to revisit or fix it some day.
Trim1/2+3 without a resistor in parallel might wake up the neighbours when the trimmer fails one day, causing this gain stage running open loop. Trimming R7 instead will give less annoying results in case of parts failure.

Click to expand...

aahhh of course.. it was that way.. but.. never mind.. thanks! What kind of parallel R are we talking about? And do I really need the pots in the schematic even if the pots will not be connected to the boards? Or do I only have to describe them?

Harpo said:

But then it takes me ages to turn it into a board in Eagle. At one point, I had a nice layout, and after that, the making the actual pcb with photosensitive boards and a light unit is pretty easy. But I had made a mistake and now it is taking me hours again to get it into a board. Are there any rules of thumbs or guidelines to make this process a bit easier? Or is it just a matter of keeping on trying?

Click to expand...

Keep on trying. Every iteration process will probably get you to a better layout than the 1st try, but maybe only a [ripup] of the wrong routed traces already gets you there, so you don't have to start from scratch. Just remember to have both files (schematic and board) open while editing, else the result will be inconsistent.

Click to expand...

OK.. thanks a lot!

erikb1971 said:

What kind of parallel R are we talking about? And do I really need the pots in the schematic even if the pots will not be connected to the boards? Or do I only have to describe them?

Click to expand...

From your schematic the pots will be connected to the board, else they wouldn't make much sense. Doesn't matter if you use pots footprints or have them connected thru some piece of wire, but footprints for these specific pots (pin spacing is dependant on type of pot) will give you the option for a direct mounting/connection at the desired location on pcb. The trimmer will have a footprint anyway, but this more likely will be a log taper pot as well. Value of a resistor in parallel to this rheostat will depend on the not shown pots/trimmers value. Having parts values in schematic is easier to follow than only parts designators with designators values on a seperate sheet/BOM.
When revisiting your schematic to add a 0V reference voltage symbol to your bottom trace, you might as well add some missing parts, such as protection diodes to prevent a momentary reverse connection of the 9V batteries, cap at the neg.supply rail, pcb mounting holes, ...

adjusted schematics

Is R10 in the right place? And considering the 100K Lin trim pot, what value should it be?

Cheers

Erik

erikb1971 said:

adjusted schematics

Click to expand...

partly adjusted

Is R10 in the right place? And considering the 100K Lin trim pot, what value should it be?

Click to expand...

Yepp. 100K trimmer (why do you need up to 40dB gain in this stage when dropping 6dB in front and another 6dB behind ?) as already said will more likely be a log taper pot. Resistor in parallel maybe 100K as well, giving a 50K total feedback resistance in the pots full CW position for 34dB of this non inverting gain stage. With your lin taper trimmer/pot, the 1st.20dB of gain is within 10% of pot rotation, 5dB of gain is within the last 60% of rotation. A log taper will give you a more linear dB increase.

Partly adjusted.. grrr.. pfff..

Harpo said:

When revisiting your schematic to add a 0V reference voltage symbol to your bottom trace, you might as well add some missing parts, such as protection diodes to prevent a momentary reverse connection of the 9V batteries, cap at the neg.supply rail, pcb mounting holes, ...

Click to expand...

The 0V reference at the bottom trace. Hmm... I really lack basics in this aspect. For me.. that trace is an extension of the shield in the guitar cable. I think that is what I would call ground. Why add a 0V reference to that? Or is that just another word for ground?
Protection diodes for the connection of the 9V battery: It is not going to be a stomp box, it will be connected to a power supply.. do I still need them?
Cap at negative supply rail... eeehhh  ??? NO clue what you mean with that...
PCB mounting holes: those will come when designing the board right?

Hope I am not annoying you.. this newbe is really trying!

erikb1971 said:

The 0V reference at the bottom trace. Hmm... I really lack basics in this aspect. For me.. that trace is an extension of the shield in the guitar cable. I think that is what I would call ground. Why add a 0V reference to that? Or is that just another word for ground?

Click to expand...

From your schematic you have a 18VDC supply connected to your opamp. You called it +9V and -9V, but without a reference connection to the PSUs 0V or the 2x9V batteries series connection this would be floating. You could as well have called it +18V or +12V and -6V or whatever. With 0V connection established, the opamps now can operate your signal in reference to this potential to swing more or less in positive or negative direction.

Protection diodes for the connection of the 9V battery: It is not going to be a stomp box, it will be connected to a power supply.. do I still need them?

Click to expand...

No, but wouldn't hurt either to play safe if you change it from a mains powered PSU to battery supply one day.

Cap at negative supply rail... eeehhh  ??? NO clue what you mean with that...

Click to expand...

Similar to C11 that is connecting close to the IC between your positive supply rail and 0V reference voltage, but now for the negative rail. Watch parts orientation for this polarized cap. You might bypass both electrolytic caps with maybe 100nF c0g caps.

PCB mounting holes: those will come when designing the board right?

Click to expand...

Mounting holes with maybe 3mm diameter are a part in eagle as well. If you don't have these in your schematic, you couldn't place them on your board layout.

conceptually I understand what you say about the reference to 0V. Sort of.. I think. But does that mean that I just have to connect it to the bottom trace?

Yupp. Better use the 0V or GND symbol instead of the PE symbol at C11. This is not safety ground.
A through-hole solder pad for this 0V PSU connection (similar to your +9V or -9V) would be a nice to have as well.
A molex- or screw terminal connector (at whatever avail.pin spacing) for all 3 PSU potentials might be overkill for this project.