Help with Four nano ch340g on one board

this is an off the wall thing I need to do, so I have questions. I have uploaded the schematic that I think would work for one of the 4 sections. What capacitors should I select for the crystals? Also since there are going to be four of these on the same board along with two 4 port USB hub circuits on the same board, (Which I still need to design) that will be a total of 10 crystals, can I use the same crystal for all four of the atmega and use the same one for all four of the ch340g chips? Obviously one will be 16mhz and 12 mhz. Also, if anyone has any recommendations for the USB Hub portion of my board, please chime in and let me know, as this is WAY out of my comfort zone of hardware. I do hardware professionally, but never did something like this before.

If I do have to use all 10, do I need to completely isolate and RF shield the individual circuits? Let me add in right now that I will be designing an actual PCB for this. Also is it okay to go with through-hole Quartz crystals so they are easier to solder? Or do I HAVE to use the ceramic resonators? Not to worried about making this as compact as possible considering most of the components are already compact and this is all going on a large 68 pin card edge connector type board. Thanks for any help that I can get with this.

What is the application?
Why don't you use Nano and if you are going to make a PCB, put headers on the PCB for the Nano to plug into.
The Nano is so cheap, why are you repeating, the hardwork has been done.

Here is an example on the prototype of a project.

Tom.... :smiley: :+1: :coffee: :australia:

Thank you for the reply. I am well aware of this solution already. Just like In the OP, I said I need four of them on one board with a USB hub circuit. These will be permanently attached to the host via USB. It is a 68 pin card PCB. I need everything integrated onto the one PCB, not a bunch of headers and cables all over the PCB... Furthermore I may have a lot of flat plane space to work with, but not exactly vertical space... there will be several other cards on either side of this card.

Also, this all has already been "prototyped" on breadboard and whatnot the way you are suggesting. I am ready for the final model and all I have left to build is this card. So again like the OP, is my reverse engineering of the ch340 nano correct? I am well aware as well that I left out the regulator, because I don't need it...

The whole point of using a PCB is to eliminate the interconnecting cables, but that does not preclude you using 4 Nanos plugged into sockets on the PCB

From this schematic I found Googling;

The CH340 crystal has them "omitted".
I had a look at a coupe of my Nanos and none of them have the two caps on the crystal.
Unfortunately you cannot parallel up the crystal pins of the Nanos because each Nano has a driver circuit for it.

Another way would be to edit the Nano fuses to accept an external Oscillator and fit a 16MHz oscillator block to supply all of them.

Hope this helps.. Tom... :smiley: :+1: :coffee: :australia:

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These will be permanently connected to the host via USB. Please read the whole post... I hope that I'm not coming off as rude or anything, but it has been stated already what I intend to do with this project... Just asking for some expert advice on the architecture of the NANO CH340G version that comes from 3 party vendors.

Thank you for this information. Wow, that schematic is as simple as I suspected! The reason that I put the caps on the crystals in my schematic is because I don't intend to use the ceramic resonators if I don't have to. Every time I have used just normal metal can crystals in the past I have had to put caps in place. So what this is telling me is that I don't even need them? I'm just a little confused here... Can you explain to me why they would be omitted? Above all, this is some really good information here. Honestly I could have probably just googled the schematic for the knock off nano board, but I have trust issues LOL. This one looks pretty close to what I found with a metre and scope on a physical board with parts that I don't need being omitted from my hand drawing.

Here is an example of the board that I will make with the Nanos and USB hubs. This is another one of the boards so just use this photo for reference only.

Hey, also, do I need to tie all the unused pins on the 328P to 5v or gnd via resistors (Pullup/Pulldown)?


Yes that would be my view too, why I don't know, you may have to put some pads down in case you need too.
I have had a look at many CH340G circuits on Google and they all seem to have 22pf caps on the crystal as standard.

Tom... :smiley: :+1: :coffee: :australia:

Putting 4 Nanos in sockets on the PCB does not preclude doing this and, as you will be designing the PCB you can position the Nanos as you require to create a neat arrangement of USB leads

Okay, will do. I'll put the pads on there just in case. always good to have more options on a PCB than just enough, this prevents waste! Love it.

I'm not sure if you are actually reading anything here or not, but I will say it again... I do not have a lot of vertical space on the board! Also it is completely pointless to hack up USB cables and have the routed and soldered down to a final product. This thing isn't going to look like some high school science project! I even uploaded a picture of one of the boards for reference. I only have about 6 - 8 mm between boards as it is. If you can find me a NANO compatible board with a header for the USB as well as the I/O pins, that would be an option then, because I can do short "Transistor type sockets" to plug them in, but until than, I need to do it this way... With a quick google search, nothing of the sort came up...

So how much vertical space do you have ? You have not said

Where have I suggested that ?

You said to create a neat arrangement of USB leads... What else would you mean? I already said now twice in this thread that I will be literally building USB hubs on to the same board... That would mean that I would have to hack up the USB cables to go down on to the same board that the NANOs are mounted on. . .

What would be really nice is if someone had already made a NANO compatible board with a M.2 connector on it that ported out all the I/O and the USB. I could get on board with that solution! :slight_smile:

I did say is post 13... 6 to 8 MM

Would be nice if the Nano were available in a castellated single-sided board, but even the Nano Every and Nano 33 series of boards do not bring the USB connections out to the castellated connections. Probably not a lot of market for intra-board USB communications on a processor that supports I2C, since the USB does need a hub.

In terms of wanting to use a common crystal oscillator for multiple devices, would your application work with the atmega328 running at 12MHz, so it could share the oscillator with the CH340?

Thank you for the reply. I believe so.eone tried to run the 328p on 12mhz and it didn't work. I don't mind using g several crystals to accomplish this. Pretty sure that I can isolate the individual circuits properly. The castellated option would work too. The other thing I'm a bit shady on is if I need external pullup/pull down resistors on the unused pins of the micro. Please refer to my OP schematic to see what I mean.


I have been searching around and found the Mini Pro board. By the looks of it, it is basically a NANO with the USB to TTL chopped off of it. Would I be able to hook these boards up to a CH340G and get the same result as a NANO and still be able to use it hooked to USB all the time?