Adding ESD Protection on Miuni32

ATmega32u4 reference does not delve into the details of ESD protection in the USB circuitry. It merely mentions this:

Although TVS chip is simple to apply, I can’t be too careful since there is more than one type. And since ESD is something I can’t readily test on my own, I must make sure the choices are effective. Searching on StackOverflow led me to a few useful posts. This one discusses how 2 TVS diodes have the exact same SOT-23 IC packaging, but functionally very different (one is unidirectional while the other is bi-directional). To be honest I am still not clear on when to use which. I think the gist is that bidirectional TVS chips are used for data lines (such as USB D+ and D-), and unidirectional ones are used for DC circuit.

My 1st choice is TPD1E10B06 from TI:

As you can see, it is a dead simple part. It is standard 0402 package, bi-directional and can easily be reworked if needed to. The only downside is that I need 2 of these… and that it actually doesn’t support USB 2.0.

My 2nd choice is the following, found in this ESD guide from TI:

The ESD122 is a small bi-directional 2 channel ESD protection diode. The price is right and it is very simple to use. The packaging is 3X2SON, which is difficult to work with hands, but luckily I don’t plan to do that.

3rd choice is the most expensive, but the most simple solution CGA-MLC from Bourns:

This comes in 0402 / 0603 package. Dead simple, but pricey especially when I need a pair of these on every Miuni32.

Miuni32 Rev.2 Status

The original estimated shipping of Miuni32 quoted in Group Buy #2 was this month. Unfortunately, we are past the first week of October already and I am still a few weeks away from receiving a few samples. I would love to skip this sampling process altogether, but because of the few changes I made, I would like to tread carefully. Things I have to verify include changes I have made
(let’s call this Rev.2)  to the original Miuni32 PCB design include:

  • ESD protection on the USB circuit
  • Improved 2U stabilizer location (Plate still compatible with Rev.1)
  • Update the logo and other miscellaneous graphics on the board 

I should be receiving a few sample boards again in 2 weeks. If all checks out then, I should receive the rest of the order towards the end of the month. Fingers crossed!

Meet the Ingot

A high profile, top mounted, weighted case for the Miuni32 PCB! Brought to the world by u/Haaaaaandrew and u/Tesletron. 

Here are design features of the Ingot!

  • 7-degree angle
  • 3 layout options: full grid, 2u (left shifted), 2u (right shifted) [the plate in the renders only shows left shifted – actual plate has proper cutouts]
  • 3mm brass or copper plate
  • Massive brass or copper weight -Custom cut 3m bump on to span the bottom of the case (think m65-a style rubber feet)
  • Your choice of polished or raw brass or copper features
  • Support for R1 and R2 PCBs
  • Manufactured in the USA (plates may get cut abroad)
  • Expected kit price is $325-$425
  • Available colors (May change)  :
    • Black
    • Silver
    • Rose Gold
    • Orange
    • Purple
    • Blue

This case does not have a defuser so the PCB’s under glow won’t be leveraged by this case.

Group Buy #2 Status Update

Miuni32 – Phew, the 2nd Group Buy has officially ended (although you could still participate through for the next 2 – 3 days). I am already in the talks with, estimated to ship in October of this year! 

Premium Aluminum Case for Miuni32Still waiting for the prototype. Unfortunately it did not arrive on time for the Group Buy #2 window. So I will have to figure out how to accommodate the aluminum case GB participants down the road. 

It was nervous 3 weeks or so and I am glad things have gone as well as it did!

My review of

I have been using for more than 3 years now. I initially started off with OSH Park because I loved the fact that they were in the USA close to my home, and that they had the iconic purple PCBs. However their cost became out of my budget quickly when the time came to scale to larger quantities. is the 2nd PCB maker I ever tried personally, produced all my Miuni32 PCBs through them, and I have not had any reason to try any other in the past 3 years.

Top 5 facts about PCB

  1. Based in China. Will get back to you later on this.
  2. Active on SNS – they actually active in that they take participate on Twitter
  3. 1 stop shop that uses quality components (as far as I can tell)
  4. No hidden fees. What you pay is what you see in the invoice.
  5. Quality. Never once was disappoi nted.

Top 5 Likes

  1. Efficiency. is based in China, and during their business hours, you will get extremely prompt responses via emails and chat. Daphne – I don’t know if she’s real, but she’s the overseer who’s always prompt.  I used my email 100% for the communication and exchanged some 70+ emails on a single order. They were always professional and extremely efficient.
  2. Their DHL shipping *literally* takes 2 days to show up at your door in the USA. The shipping cost is calculated based on the weight and volume, and I paid $84 USD for an order of 200 assembled PCBs that are about a size of a large cellphone.
  3. When things go wrong, they are always extremely helpful. Things go wrong. DNP parts could show up soldered. You may have found out an error last minute in your design. Let me tell you, they will literally go talk to engineers on the floor and find things out and send you back videos and photos to let you know what exactly is happening.
  4. They actually tested every single board at no extra cost. Granted, there is no way to tell if they actually did what they said they did, but judging by video and photos, at least they ran the test on some portion of the order. This is a huge relief for a first timer like myself.
  5. Communication (again). Things get lost in translation. I asked to get the scraped parts along with the finished boards, but they forgot. They found and sent it to me promptly at no charge.

Top 5 Dislikes

  1. None… perhaps I am just an extremely optimistic and positive guy. I couldn’t come up with 5 dislikes.. Let alone one…

Top 5 Recommendations

  1. Check your BOM, schematics and special requests one more time.
  2. Break down your process. I asked to get 3 bare PCBs to get sent to me before they went ahead and assembled 200 of them.
  3. Once the bare PCB checked out, I gave them a green light to go ahead and assemble the boards. Again, I asked them to send me 3 finished boards.
  4. Run prototypes. Before I submitted the big order, I ordered bare PCBs which costed a little less than $100 all in all, hand soldered the boards, and tested them.
  5. Check Chinese national holidays. I wasn’t aware their Thanksgiving holidays were like a week long.

Thanks for reading this far, and please consider using my referral code.

I don’t get any compensation for the referral other than that I get a small discount on the next order of PCBs from It will help me reduce development cost, but more than anything I wholeheartedly recommend their service.

Miuni32 Aluminum Case is coming!

Good morning everyone! This is Adam from The GB2 of Miuni32 is currently going on (only $35!), so make sure you get yours if you haven’t :).

One of the questions I get asked a lot is “Adam, but what about the case!?”. The answer to my question is usually this:

  1. Check out u/lxkhn and u/jolimon
  2. Go on your own way and make a case yourself

And now there is the third option:

  1. [NEW] Participate in GB for an over-the-top aluminium / corian case which u/Haaaaaandrew and u/Tesletron have been working on. More images here.

The exact details on the colors and the material have not been decided. So please come on over to the Discord channeland let your thoughts be heard. I am personally very excited for this development.

Price? It is not decided yet as well, but obviously the more of us participate, the friendlier it will become. One of the reasons why I reduced the price of Miuni32 PCB from $60 to $35 is so that we can put aside extra money on a case for it. So if you are concerned about the price of this aluminum / corian case, you already saved yourself $25 ;).