From Cerb 40 v1.1 to v2

Hi there :wink:

I am working on a project with a Fez Cerb40 v1.1.
I need both 5V and 3.3V on this project.

My first prototype has 2 regulators, one for 5V and one for 3.3V, connected in series with an external 9V wall wart.
Runs fine with this setup.

However, I see that GHI now only sells v2 with added onboard regulator and cap, so I guess I will have to deal with that.

My project only uses USB for firmware update, and I want to let the possibility to the user to use a common regulated wall wart.

I guess I can keep one 5V regulator and connect this to VBUS on the Cerb 40 v2.
This will feed the internal regulator and it will work.

But what will happen when both wall wart and usb will be connected at the same time?
I read on this forum that this will work fine but I also know that paralleling voltage sources is not really something to do because voltages may be slightly different (and I think USB specs say that voltage might be between 4.75 - 5.25V, which is a rather huge tolerance).

Any opinion on this issue accepted :wink:

Best regards,

Please take a look at the schematics. It will help a lot.

VBUS is connected to the regulator but also is exposed to you. This means you can use it to power your own circuit or you can feed in 5v if you do not want to use USB. Of course you can always remove the regulator and then you will be compatible with old cerb40.

You can also order old cerb40 if you need volume.

Welcome to the community.

Hi Gus,

Thanks for the warm welcome and for the bloody fast answer :wink:

I have the schematics and I know that I can provide 5V to VBUS pin.
In fact, the only thing that bothers me is sending 5V to this pin while the USB cable is connected.
This means 2 voltage sources at the same time.

See 1st post:

Correct and that is why i said if you are using USB, like the module is inside an enclosure not exposing USB. Hopefully one of the options will work for you.

Problem is I can’t prevent the user from plugging both USB and wall wart at the same time.

Looks like I either need auto power supply detection (like in some Arduino board) or stick with the older Cerb 40 design.

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or remove the regulator

Obviously :wink:

I’m in the same boat. From the start I liked the [em]option [/em]of getting a Cerb40 with an installed regulator.

But the improved version involves paying 5 dollars more and removing parts every time I build the board I designed around the original.

Buuuut I’m not buying large quantities, and I guess we are in the minority here.

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@ FireyFate Looks like it.

But you need to see why it was done that way as well.
I believe when it (Cerb40) was introduced there were request to add reg and cap and no real objections of not doing that. It seemed that it would benefit more users with these parts added.

I understand that it is easier to start with the added reg and cap.
But Cerb40 was designed to live permanently in a product, not as an easy to use powerful arduino for beginers, there are other Fez boards for this (although I admit the price tag of the cerb40 board certainly help beginners to do this choice instead of the other easier to use Fez boards).

I want medium to large quantities of the v1.1 version, I’ve asked the sales guys for the minimum quantity, still no answer.

I think GHI either:

  • need to offer both versions in their catalog
  • need to clearly state the minimum quantities needed to buy the 1st version. But if this number is too large, maybe I will think at designing another compatible board and send the design files to a fab house to have my own boards.


remembering that you’re TOTALLY allowed to make your own boards based on the open designs that GHI offer, it’s always an option

Thanks Gus, good to know.
I will talk about price and shipping delay to the sales dept, as this is a bit OT.

Yes, that’s why I went the cerb40 road.
If for any reason they decide to stop the production, I can make my own boards, which is very important when a commercial project is based on these boards.