finding short on motherboards with a shorty (with display)

[lux]

Really great work jdobry. I would like to buy one. I am from Germany. Can you reserve one for me? When are you ready for shipping?

[Miti]

I’m interested in the assembled boards as well. See that I said boards.

[trackersoft]

Put me down for one when you get ready! Great work!

[jdobry]

Hi all,
I am little bit surprise by interest to buy it. Ok, I am just another hobbiist, therefor I am not able to saturate request.
This is my final inventory for this moment:
4 complete devices or just complete PCB. Price is 35EUR + shipping fee in both cases. (complete device is possible to send only to EU, PCB as 50g letter anywhere)
3 incomplete PCBs (see to this thread history)

For complete device I have reservation in this (datetime) order: ddrl46(thread), prog willem(email), clearchris(thread), Martin72(??thread), lux(thread), Natale Maniaci (email), Miti(thread), giovannirat(PM), trackersoft(thread)
And I have only 4  to sell

It will be ready to ship next week. I will respect this reservation order, but without confirmation till end of week i will accept next in order.

Contact me by PM, shipping fee depend to destination and selected shipping.

PS: 3 incomplete PCBs is still free. But I don't have components to finish it.

[zoltanh]

Hi,
Referring incomplete boards could you, please, list the missing components?
Thank you.

[jdobry]

Incomplete PCB you can see on the photo.
https://www.eevblog.com/forum/testgear/finding-short-on-motherboards-with-a-shorty-(with-display)/msg4618300/#msg4618300

[timeandfrequency]

Hi jdobry,

Thanks for your comprehensive work and the sharing of that interesting project.

May you provide some explanation on how you choose the value of L2 (6.3 nH) ?
I checked against kripton2035s schematics and the power supply on the bottom is new in the design, because I guess, of using much smaller AAA batteries. kripton2035 used a 9V battery.


I understand that U2 is a boost switcher that clocks around 2 MHz to create the '3V3' digital power supply rail.
A second filtering around L2, C1, C3 and C4 leads to the analog power supply rail labeled 'A3V3'.
The latter powers the MCP3421 which is a really low power device (typically 145µA during conversion @ Vdd = 3V) and the AD8628 whose supply is 1mA.


By using the Thompson formula, the 2nd order LPF built around L2, C1, C3 and C4  (6.3 nH and 10.2 µF) has a calculated corner frequency of 627.8 kHz

6.3 nH is a really small value : it corresponds in air/vacuum to the inductance of a 1 mm diameter free hanging wire having a length of 1 cm.

What is the reason for keeping the corner frequency well above 500 KHz rather than setting it to a much lower value, that would filter out all of the switcher and digital noise coming from the µC, down to a few kHz ?

By changing L2s value to 47 µH (RDC= 5.8 Ohms Imax = 90 mA), which is about the biggest possible inductor value available in the 0603 size, the corner frequency becomes 7.2 kHz.

[jdobry]

About L2:
I want to use low resistance inductor just to reduce main noise source from step up (2MHz). I prefer low-resistance because I have bad experience with standard feritte pearls - unwanted feedback caused by variable current to power line voltage on another project.
But to be honest this value I just test and it works perfectly. You are right, selected inductor looks like piece of wire on ceramic substrate. Few additional mm of path on the PCB could made same service.
But I want to use 0603 part to allow change in problem case. I thing that "0R" resistor could work on this place too, but I don't test it.
Similar story is R17. I just want to have 0603 part on this place to define single point of connection between signal ground and main ground. A am using 0R, but i thing that 10R (for ex) will work too.

PS: all devices and PCBs are reserved or sold. For this moment I don't have plan to make more series (it is not my business, but just hobby project). I could co-operate with some company on the production, but made it manually is fine only for prototypes.

[natman69]

Very interesting project!

@jdobry: maybe you can manage to sell a kit of components and a pcb, making a small profit!!!

Or we can organize in this thread a group buying of all components, avoiding making multiple single orders on aliexpress.

[jdobry]

Buy & sell isn't technical problem for me. I can order for ex batch of 50 PCBs. Price will be less than $30 each include all parts (one side fully assembled, side with buttons and OLED in package as parts) include 3D printed case, 1m of cable etc. And sell it as DIY kit with price around $40.
But I have problem to do it legally (taxes, custom declaration, invoices, accounting etc). And of course worldwide shipping.
By my mean it need business partner in Cina a send it directly from China (they have experience and possibilities how to make this business). And I don't have trustful contacts for it.
But I thing that market for this device is too small to try something like kick starter and make business by this way.

Jiri

PS: series production can need some minor changes. For ex replace D2 by 2 diodes (BAS40-05-TP isn't available in JLCPBC SMT assembly service now), change type of Q1, change U1 by another chip (TPS7A20185PDBVR isn't in JLCPBC SMT assembly service now) and minimize parts in second side of PCB.

[natman69]

Hi Jdobry,
Of course, shipping worldwide is not easy. I was thinking really to a simpler plan: just count people interested in this thread and, at beginning, manage buying parts for all. You just will send to EU to avoid any custom declaration and taxes. After if you see that lot of people are interested worldwide you can think a different approach as a kickstarter campaign.

[jdobry]

OK, I can make group order for EU members.
Just one side SMT assembled PCB + parts for second side (buttons, beeper, OLED) + needeles + 3D printed parts. As DIY kit (I don't have production capacity)
Do you have idea how to organize it? Today I sold just 4+3 pieces and it took plenty of time to communicate with everybody, check payment, don't make mistake in addresses, etc.
I has some experience from history (we made bunch of 3D printers in group). And we are using shared spreadsheet. But it need 100% trust to anybody and it is possible only in closed group.

Jiri

[natman69]

My suggestion is you fix the price of the kit to cover all your costs. Shipping cost will be added after, depending on the destination country in EU.
Then wait people to ask for a kit with a PM. At a certain point, you will close the reservations. Decide also if you want collect money before ordering components or just when you will have kits ready to be shipped. Prepare a template with mandatory info for the shipping and send to all the buyers. This will help you to manage the shipping. Decide also how do you want to collect money (paypal, bank transfer, etc).

[jdobry]

OK. I can organize group order. In few steps:
1) fill form as reservation to count aprox batch size
2) Calculate final price (it depend to batch size). I expect less than $40 for complete DIY kit and less than $30 for PCB kit. Complete kit will be available only in EU (shipping)
3) wait for confirmation of pre-orders (pay it in advance) ~ February-March
4) shipping ~ April~May
It will be just as PCB kit (one side assembled PCB + all parts for second side) or DIY kit (PCB kit + 3D printed cas + needles + cable, only for EU)
Do  somebody have better idea?
PS: I can start this after next week. Next  week I need to send current batch.

[mariush]

Are you still using the DIN connector? 
If you only use 4 pins for the leads, why not repurpose  a 2x2 mini fit jr (cpu 4 pin) or 1x4 mini fit / milifit (smaller) and that would allow lower height devices and easy to crimp lead wires to the connector.

[jdobry]

Are you still using the DIN connector? 

I don't use any connector. https://www.eevblog.com/forum/testgear/finding-short-on-motherboards-with-a-shorty-(with-display)/msg4618285/#msg4618285

[lux]

I think the idea with the two kits is great and your roadmap is good.
You should prepare some photos for each kit so everyone can see what they are getting.
I think it's really worth the money.

[clearchris]

I yield my spot in the initial list.  I'm so slammed at work, I doubt I'll be able to even look at it for a few months.  Give my spot to someone who can do something and provide useful feedback in the near term.

Hopefully I'll be able to surface and get in on the next batch.

[Martin72]

Thank you jdobry ! 

[Martin72]

It´s really not necessary in this case, but just for fun I´ve grabbed some Isabellenhuette precision (0.5%) shunt resistors and measured them.

0R01 : 0.0100
0R05 : 0.0499
1R0  : 1.0050
(best values when contact is "100%")
This is not bad...

[PeterSpie]

Hello everyone, and special hello to jdobry for buidling this great shorty pen.

I am planning on building the pen also, I have ordered the PCB's form the list on gitlab.

Now, I want to order the parts, but I can't find one vendor that has all the parts in stock.
I have checked Mouser, Conrad, RS-Online etc... etc...

There is a beautiful BOM in gitlab, but I just have problems with searching for the parts.
Is there anyone here who has found all the parts, so that shipping costs can be reduced?

Regards, Peter

[PlainName]

If there are multiple vendors then perhaps one could arrange a group buy so the vendor with just one part gets an order for multiples. Obviously not as good as getting everything from one place, but with enough buyers in the group it could make a difference

[miklas]

Hey, jdobry may I ask what are those probes? and where to buy them if I may?

[abeyer]

The link in the BOM (from gitlab upthread) is https://s.click.aliexpress.com/e/_DBPslrD

[Ocela]

Greetings to everyone on the forum!
Great project, jdobry! I will definitely repeat!