The offset design allows for the use of the onboard 5v power supply as a voltage source which has a convince advantage. It could also be done as a SMD setup. But using 5v onboard can also be limiting for specific scenarios like overclocking 5v cpus.

This is why I went externally powered on my device. Also mine has option jumpers for setting many different tweaks.

If you want to integrate my tweaks into that design feel welcome 😀 some peope will prefer the onboard voltage source design for convince/tidyness. Even if it is limiting in some scenarios.

I've updated my own PCB to a 4 layer design. It's pretty much the same just with vin and vout on their own layers and the top and bottom layers have the traces between pins mirrored, it should keep the people who are concerned about interference happy.
I just felt like a trying a 4 layer PCB and here we are.

Add tweaks! :p

Sphere478 wrote on 2023-01-14, 19:08:

Add tweaks! :p

Honestly since this is largely someone else's project I think it would be for them to set the feature set of this. I just felt like taking a stab at building in an onboard regulator to see how it goes.
Going 4 layer made this PCB much easier to make and implement the tweaks as you suggest but it is up to ScrapComputing. They did reply to my first PR and I decided to close that and make another from scratch.

I hope this is actually a good design and that this hasn't been a waste of time. I know very little about power regulators and design, but I've done some research and I think this isn't completely terrible.
I would be very interested to see this on a scope just to see the ripple but I don't own a scope myself and JLC are not making "economic" 4 layer boards this month.

Needs caps as close to the cpu power pins as possible with short high amperage connections. See the sxl2 interposer in my pcb projects for ideas

The next version of mine I will try to add these. It was much easier on the sxl2.

I was thinking there today

An overclockers edition of this PCB that has a little pot to tune the voltage between a pretty narrow range so that the pot drifting a little shouldn't impact anything. I wonder if that can be done.
IE: the pot is in parallel with another resistor and the two together set the voltage.

I've been up the walls with some home improvement and cleaning taking up my spare time but I might have the time to work out the math at work this week to see if it's doable. It could be good and for people who don't want to set the voltage then can just have a resistor to set the voltage with no pot, no change to the PCB just the BOM.

We shall see. what would the range be, like 3 to 4 maybe? I'll have to check some amd 5x86 overclocking threads to have an idea of range.

CalamityLime wrote on 2023-01-17, 23:31:

I was thinking there today […]
Show full quote

I was thinking there today

An overclockers edition of this PCB that has a little pot to tune the voltage between a pretty narrow range so that the pot drifting a little shouldn't impact anything. I wonder if that can be done.
IE: the pot is in parallel with another resistor and the two together set the voltage.

I've been up the walls with some home improvement and cleaning taking up my spare time but I might have the time to work out the math at work this week to see if it's doable. It could be good and for people who don't want to set the voltage then can just have a resistor to set the voltage with no pot, no change to the PCB just the BOM.

We shall see. what would the range be, like 3 to 4 maybe? I'll have to check some amd 5x86 overclocking threads to have an idea of range.

Well, you basically make a voltage divider on some regulators and it gives a reference voltage the trim pot would let you adjust that.

Range would probably ideally be like 3.3 to 5-point something so that overclocking of 5v cpus can be accomplished. But this isn’t possible using onboard without some sort of boost circuit. (Or external power)

You could use a low drop out regulator/buck style and a jumper that passes 5v to the cpu so you could get true 5v as the max option.

Sphere478 wrote on 2023-01-17, 23:39:

Well, you basically make a voltage divider on some regulators and it gives a reference voltage the trim pot would let you adjust that.

Range would probably ideally be like 3.3 to 5-point something so that overclocking of 5v cpus can be accomplished. But this isn’t possible using onboard without some sort of boost circuit. (Or external power)

You could use a low drop out regulator/buck style and a jumper that passes 5v to the cpu so you could get true 5v as the max option.

I can't do higher than 5 without making a more complex circuit. Personally I'd think that the majority of people looking for a voltage adapter would want faster 3v 486's working on 5v motherboards. I'm open to being proven wrong but I doubt it's worth it. Maybe a fan header would be worth it though, 5 volt fans are decently available, there is the obvious noctua but I have some sunon ones I pulled from things too.

Hard to say. I imagine there are both camps. Maybe more for 3.3v though 😀

There wouldn’t really be another good way to over volt the cpu without over volting the whole system. So a interposer seems to be the go to.

I took a go at making a circuit with limited range on the voltage.
This is what I came up with and the over all resistance is still inline with the datasheet.

There is some wiggle room for a slight over volt and under volt and you should need to turn the pit a good bit for a change in voltage so drifting should be a non issue. Best part is that it'll be super easy to just set the voltage of 3.3 or 3.45 with resistors for those who don't want to fiddle with the voltage.

What do ye think?

That looks like resistance movement would be quite small indeed.

Could not this also be accomplished with two pots in series? (Would give more range) though be more confusing for the user. Adjusting two dials at once.

CalamityLime wrote on 2023-01-18, 13:22:

I took a go at making a circuit with limited range on the voltage. This is what I came up with and the over all resistance is st […]
Show full quote

I took a go at making a circuit with limited range on the voltage.
This is what I came up with and the over all resistance is still inline with the datasheet.

There is some wiggle room for a slight over volt and under volt and you should need to turn the pit a good bit for a change in voltage so drifting should be a non issue. Best part is that it'll be super easy to just set the voltage of 3.3 or 3.45 with resistors for those who don't want to fiddle with the voltage.

What do ye think?

Your schematics shows R2 as 40.2 ohm, not k. Confused me a little until I read the table below 😀

H3nrik V! wrote on 2023-01-18, 21:29:

Your schematics shows R2 as 40.2 ohm, not k. Confused me a little until I read the table below 😀

Ah, oops.
Yeah it's 40.2k i always go into LCSc and look for common sizes so stock should be available. 40k worked math wise but far less stock of 40k so 40.2k it was.

Still I'm pretty sure that should work, I'll have to try to find room for the parts on the PCB at some point and double check the range to see if it's all good. The datasheet for the regulator (if I'm reading it right) seems to imply that it wants a drop of just over 700mv at least. So that's where the 4.2v comes from.

I took a go at adding the pot to the PCB.
The layout of the PCB changed a bit based on feedback from the Retro Web.
Github: https://github.com/LimeProgramming/486SocketB … r/4-layer-kicad

Rigo (previously known as cats) provided a lot of feedback and made their own variant of the layout but they haven't uploaded anything to github yet.

Very nice! :p

It’s worth noting that there were a few different pins used for multipliers on the 486 socket platform. So your switch won’t apply to all cpus. I think you already know that though. You should note on the silk which pin that jumper is using. That’s one of the reasons my unit has so many jumpers 🤣.

I’m thinking of doing a respin of mine using a few resistor networks to save space and make it smaller by ditching the pin map.

Dips in the center are also possible.

Sphere478 wrote on 2023-02-05, 04:32:

Very nice! :p

It’s worth noting that there were a few different pins used for multipliers on the 486 socket platform. So your switch won’t apply to all cpus. I think you already know that though. You should note on the silk which pin that jumper is using. That’s one of the reasons my unit has so many jumpers 🤣.

To be honest, not really.

This has just been about adding an onboard regulator. The only other thing I've been tempted to add is a 5v fan header but maybe that would be silly.

Thought I should just update this for the sake of completeness

Here is video 3: https://youtu.be/CLPSJ0jOQsU

I decided that I want to order a few of my own fork and I was just updating it a little bit. Improved the silkscreen a bit and changed the caps on the outside side to hopefully keep ripple down. I ran through the numbers and formulas on the dc-dc converters datasheet and the numbers are so small I don't believe them so I'm not going to share them.
so, yeah, thats all for now.

Very nice 😀