Introducing the ARM PRO MINI board - ARM Made Easy

[zapta]

How do you get the metal stencil? Do they provide it when you make a pcb with them?!

It's an extra thing that you order and they make it from the gerber files. You can get plastic ones for chip from oshstencils.com (not related to oshpark) but am not sure if the resolution is good enough for 0.5mm pitch. Electrow and others such as dirty pcbs make them from metal (laser cut) and they have better resolution.

[paulie]

I built several of zaptas boards now and was lucky to have no failures. No stencil. The way I do it is tack the chip down with tiny speck of solder on two corners then add a big glob on all the pins. Heat each side and BANG the excess solder off by rapping the board edge on a hard surface. Like zapta says lots of resin helps then you can clean it off with isopropanol. This method has worked for literally hundreds of SMD chips and no failures yet.

All but one of my boards are only partially populated but still work 100%. The diagram for the "nada" has all the components needed which is much less than the full size version and will increase chances of success. After it is working you can always add the rest later .

ps. Another suggestion is to order more than one chip at a time. Not only do they cost less but you will have backups. I am the worlds cheapest man but IMO worth a few extra bucks for such a nice project.

[dansku]

Yeah, after doing some research, I found out that there are two things that would make the work SOOO much easier and faster.

1st - As described by zapta, the stencil/metal mask.
2nd - reflow oven.

The only problem is that I'm moving to Australia for a year in 3 weeks, so I won't build one DIY reflow oven now  , maybe when I come back!

How shitty would it be to try to reflow on a working small electric oven?

[uChip]

How shitty would it be to try to reflow on a working small electric oven?

According to Nate, their founder, SparkFun ran their business for a time using a hotplate for reflow.  You might try that method.  Or a toaster oven is not that different so I would think that would work as well.

Zapta, this is an awesome design.  Thanks for publishing!  Have you approached SparkFun or anyone to make these available commercially?  Seems like a good opportunity all round since not everyone is comfortable with SMT work.

  - Chip

[Mechatrommer]

...with the mbed online IDE. It's a very nice environment considering that it's browser based...

no! browser based is not nice for oldtimer like us. give us standalone based and we may consider programming with... and for us who have other things to do, we just prefer to buy it from you (if the price is reasonable) we dont have time to mess redesigning the board and ordering from pcb fab house and plethora of components suppliers. nice effort though on the hw side. after you settle the sw standalone ide side, you may expand your idea to larger pin count such as arduino mega, because mini is too limited for some larger application such as full color tft with other stuffs to do.

edit: i noticed the lpcxpresso now, downloading...

[zapta]

we just prefer to buy it from you (if the price is reasonable) we dont have time to mess redesigning the board and ordering from pcb fab house and plethora of components suppliers.

I may be able to supply the boards in small quantities for direct cost (or for free if it's only a few).  I will try to get the attentions of vendors such as Sparkfun and Tindie. I have a day job that pays the bills so my goal here is to make available an ARM board with great experience out of the box (I hate 'tool chains') and that can be used as starting point for custom PCB designs.

If you want one for free, send me a .bin file with the hello_world.cpp program modified to print your name and mailing address. (limited time and quantity offer).

[zapta]

I updated the u8g lib driver to work with the ARM PRO MINI. It can now be hooked to graphical displays via SPI. Here is my test unit with a 1.3" 128x64 pixel OLED, updated at 20 fps (frame update time is 8ms so it can go 100fps).



Sample program is here
https://github.com/zapta/arm/blob/master/pro-mini/lpcxpresso/u8g_example/src/u8g_example.cpp

Driver is here
https://github.com/zapta/arm/blob/master/pro-mini/lpcxpresso/u8g_lib/src/u8g_arm_pro_mini.cpp

[dansku]

I updated the u8g lib driver to work with the ARM PRO MINI. It can now be hooked to graphical displays via SPI. Here is my test unit with a 1.3" 128x64 pixel OLED, updated at 20 fps (frame update time is 8ms so it can go 100fps).



Sample program is here
https://github.com/zapta/arm/blob/master/pro-mini/lpcxpresso/u8g_example/src/u8g_example.cpp

Driver is here
https://github.com/zapta/arm/blob/master/pro-mini/lpcxpresso/u8g_lib/src/u8g_arm_pro_mini.cpp

Looking great!!

[dansku]

I was analyzing the arm pro mini schematics, and I have two simple questions.

What does the Optional A and Optional B does on the circuit?
Thanks 

[zapta]

I was analyzing the arm pro mini schematics, and I have two simple questions.

What does the Optional A and Optional B does on the circuit?
Thanks 

Optional A allows the MCU to control its USB enumeration by the host. The host will consider the board to exist only when the 1.5k resistor is pulled up. It is useful for example when switching from serial to ISP mode and vise versa, or if your USB initialization code is too slow after the reset (typically not a problem).

Without A the device exists whenever it is plugged in. To switch between serial and ISP you need to replug the board. This is exactly what I am doing with the ARM PRO NADA board (which is a very strip down version of the ARM PRO MINI).

Optinal B includes two functions, ESD protection and impedance matching. I removed both in the Nada board and everything still seems to function.

BTW, the USB connector itself is also optional. For example if you don't use USB and just want occasional firmware upgrade you can have a header or exposed pads as people do with ICSP.

BTW, I am not a USB expert so other may provide more details.

[dansku]

I was analyzing the arm pro mini schematics, and I have two simple questions.

What does the Optional A and Optional B does on the circuit?
Thanks 

Optional A allows the MCU to control its USB enumeration by the host. The host will consider the board to exist only when the 1.5k resistor is pulled up. It is useful for example when switching from serial to ISP mode and vise versa, or if your USB initialization code is too slow after the reset (typically not a problem).

Without A the device exists whenever it is plugged in. To switch between serial and ISP you need to replug the board. This is exactly what I am doing with the ARM PRO NADA board (which is a very strip down version of the ARM PRO MINI).

Optinal B includes two functions, ESD protection and impedance matching. I removed both in the Nada board and everything still seems to function.

BTW, the USB connector itself is also optional. For example if you don't use USB and just want occasional firmware upgrade you can have a header or exposed pads as people do with ICSP.

BTW, I am not a USB expert so other may provide more details.

Awesome, thank you for the info!!
Even that you can program the board using a ICSP, I think that the USB makes it even easier for people to start programing using the board!

[zapta]

Awesome! I will ship the current board to you, and you can take a look then!!
Thank you very much!!!

I will get your address on Private Messaging. 

Hi dansku, the board arrived, got fixed and will hopefully go out with tomorrow's mail.

The main problem was the soldering of the USB connector. It had shorts and one pin didn't have solder. I noticed solder paste that didn't melt so I reflew it again and this fixed the shorts. Also, the board has some white crust, probably from the flux, that I never seen before and it didn't come off easily with IPA. I wonder what solder paste you use.

The 0.5mm QFN MCU was soldered OK. It's interesting that soldering the micro USB connector is more challenging than the QFN. This is also my experience. Never had a problem with the QFN.

I think you need to refine your reflowing process. I am not an expert but others may provide more information.

I have used elecrow 5mil metal stencils but oshstencils says that their plastic stencils can do 0.5mm pitch. I have on order two stencils 3mil and 5mil so will see how this will go. The plastic stencils are cheaper and arrives in the US in few days. Will see how it will go. Placing the paste with toothpick or syringe doesn't work well for me, stencils do.

[dansku]

Awesome! I will ship the current board to you, and you can take a look then!!
Thank you very much!!!

I will get your address on Private Messaging. 

Hi dansku, the board arrived, got fixed and will hopefully go out with tomorrow's mail.

The main problem was the soldering of the USB connector. It had shorts and one pin didn't have solder. I noticed solder paste that didn't melt so I reflew it again and this fixed the shorts. Also, the board has some white crust, probably from the flux, that I never seen before and it didn't come off easily with IPA. I wonder what solder paste you use.

The 0.5mm QFN MCU was soldered OK. It's interesting that soldering the micro USB connector is more challenging than the QFN. This is also my experience. Never had a problem with the QFN.

I think you need to refine your reflowing process. I am not an expert but others may provide more information.

I have used elecrow 5mil metal stencils but oshstencils says that their plastic stencils can do 0.5mm pitch. I have on order two stencils 3mil and 5mil so will see how this will go. The plastic stencils are cheaper and arrives in the US in few days. Will see how it will go. Placing the paste with toothpick or syringe doesn't work well for me, stencils do.

Thank you for the help!
I tough that the problem was in the QFN soldering.

I know my soldering process was ridiculous, I only have the solder paste but no stencil, so what I was doing is using a toothpick to place the paste on the soldering and using a soldering iron to finish it... You saw the result.

I have the stencils coming, hope everything works better the second time. What do you use to remove flux after soldering? I had a lot of flux left on the board, which is gross and makes it look bad!

[zapta]

I am using this solder paste and it comes off with IPA. They also have a T5 type with finer solder balls but the T3 works good enough. Syringes are wasteful since you cannot return the leftover to the container so I use jars. For cleaning us use foam swabs (each lasts for many boards) and and a brush which I trim short to be stiffer (search ebay for: acid flux brush).

Never seen that kind of crust earlier. Must be from the the solder paste you are using. Try to search these forums for solder paste recommendation. May be a good topic for a new thread, good combinations of solder paste and matching cleaning chemicals and techniques. For example, I have a ultra sound cleaner, would be nice to just throw the boards in and let it do its magic. Never tried, not sure what non flammable liquid to use. I am not an expert.

http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&keywords=SMD291AX250T3

http://www.ebay.com/itm/100-PCS-Small-Foam-Tipped-Cleaning-Swabs-swab-for-Inkjet-Printer-Electronics-/290991199907?pt=LH_DefaultDomain_0&hash=item43c06d56a3

http://www.ebay.com/itm/12-Disposable-Acid-Brush-also-use-for-Craft-Glue-Epoxy-Paint-Flux-brush-and-more-/201266140243?pt=Model_Kit_US&hash=item2edc659453

[paulie]

IMO it makes little sense to get involved with solder paste and certainly stencils for one or two boards. That does seem to be popular with hobbyists, however saving time, money, and effort are never high on their list.  Regular 1% 37/63 wire solder with cheap (but plated tip) pencil iron is the key for those with "git 'er done and git 'er done with least fuss" philosophy.

I recall Youtube videos from one or two guys who actually do know how to prototype SMD the easy way. Unfortunately outnumbered 100:1 by the guys who don't. So the current hobby state of events is pretty understandable.

[zapta]

Here is Hackaday's entry for ARM PRO MINI

http://hackaday.com/2015/01/19/arm-pro-mini/

[dansku]

Here is Hackaday's entry for ARM PRO MINI

http://hackaday.com/2015/01/19/arm-pro-mini/

Congrats Zapta!!!

[Mechanical Menace]

I think I've just found the solution I didn't even know I was looking for. Thanks for the great work zapta.

[mtdoc]

Here is Hackaday's entry for ARM PRO MINI

http://hackaday.com/2015/01/19/arm-pro-mini/

Congrats Zapta!!!

Yes. Congrats! Well deserved (even if you are a wacky anti RE, anti EV 'er  ).  This looks like a really good easy ARM solution. It deserves more exposure.

[zapta]

Here is Hackaday's entry for ARM PRO MINI

http://hackaday.com/2015/01/19/arm-pro-mini/

Congrats Zapta!!!

Yes. Congrats! Well deserved (even if you are a wacky anti RE, anti EV 'er  ).  This looks like a really good easy ARM solution. It deserves more exposure.

Thanks mtdoc. Doubly appreciated ;-)

The main design goal was to make it simple and effective and a great out of the box experience. The wide selection of ARM devices and the 'tool chains' may be overwhelming. ARM tried to address it with the mbed cloud thing but I don't see it getting much traction in these forums.

[neslekkim]

Got your board today, pretty thing, and small!, need to figure out how to get it out of the printed enclosure without tearing off the usb connector (only thing to hold on), but very nice kit.

[zapta]

Got your board today, pretty thing, and small!, need to figure out how to get it out of the printed enclosure without tearing off the usb connector (only thing to hold on), but very nice kit.

The board is attached with two pieces of double tape, one below the USB connector and the other below the buttons. You can pry them gently. Heating it slightly may also help (don'g heat the PLA case to more than 50C or so). 

The case acts also as a protector during shipment. 

Have fun.

[neslekkim]

Ah, super!, I thought it was the case that very snug fit, but it was only the tape that was strong, nice!

What kind of tape did you use?, this was very much better tapes than the ones I have used before?

[zapta]

Ah, super!, I thought it was the case that very snug fit, but it was only the tape that was strong, nice!

What kind of tape did you use?, this was very much better tapes than the ones I have used before?

3M Outdoor tape http://amzn.com/B00004Z4BV . I use it a lot.



Edit: sorry for the oversize image. This is what I found on Amazon.

[neslekkim]

3M Outdoor tape http://amzn.com/B00004Z4BV . I use it a lot.

Great, thanks!