Minimal design thoughts

[hek]

@sharath-krishna

http://forum.mysensors.org/topic/510/minimal-design-thoughts/140

[tbowmo]

@Anticimex

I don't solder any pinheaders for the serial port, just putting the pins from the ftdi module in the holes on the micro board, and then holding it in place. Done the same thing for the ISP port, but it's a bit more problematic. The last two boards that I have assembled, is with pins in the ISP port.

I expect to have a "standard" bootloader in the boards (Together with a standard sketch for reading / reporting sensor values), when we receive them from China, so the ISP port is not necessary for the average user. only serial port for reprogramming (if not going for OTA).

But it might be an option for a future module, to have better access to the headers. Also might go with the nrf24 smd modules. But that's another project at the moment

[tbowmo]

@Anticimex

btw. the only painfull thing about the current layout, is handsoldering it it's a nightmare.. Almost regret that I used the new footprints for resistors / capacitors, as it makes things a lot more difficult.

[Anticimex]

@tbowmo Sure. But after a chat with @hek I believe you have dabbled with a bootloader that can flash in new FW from the external SPI flash. This is to me very interesting because that means we can deploy FW updates OTA using the MySensor library to flash the external flash, write some EEPROM byte to inform bootloader that new firmware is available, reboot to have the FW transferred by the bootloader and then boot the new FW. And this in turn means that we can transfer the new firmware signed, therefore support signed FOTA and THAT is very much interesting to me
So for me, the ideal would be that the board was preflashed with that bootloader (patched to be triggered by MySensors logic if necessary). Then there would be no requirement to have any extra headers, as you can push whatever you want, and signing can be implemented without actually changing the bootloader (headers will probably be needed during development, but that could just as well be done on breadboard).

[hek]

@Anticimex

But you would still need to set the keys...

[Anticimex]

@hek Well, not really. If you like, you can FOTA down the personalizer with your PSK and execute it by remote on a "virgin" unit Then FOTA down your application FW. It is only when your application tells the GW that it require signing, signing actually kicks in.

[tbowmo]

@Anticimex

Yes, I have a bootloader, that copies external flash, to internal. It's also verified as working, with a local firmware update where I downloaded a sketch to the micro, which put another sketch into the external flash, so no OTA in the verification phase. I used DualOptiboot from lowpowerlabs (There is a copy on my github account.)

The bootloader looks for a signature in the first couple of bytes of the external flash, if present it copies data and erases the external flash.

I just don't know what direction things are going at the moment, as there also exists the standard MySensors bootloader. If we use dualoptiboot, we need to have FOTA code in the default application that is loaded into the device, before shipment from china.

[tbowmo]

@hek, @Anticimex

if we are going to use the external flash for OTA, then it should be included in the library? So the libraray handles the OTA packets, putting data into the external flash etc.

[hek]

@tbowmo
Yes, that would be the most reliable option to allow updates un normal running mode.

I discussed this with @Anticimex earlier today and how to combine it with signing without totally flood the network with nonce requests etc.

Neither of us have the flash memory though

[Anticimex]

@tbowmo Yep. The way I understand how things work, I suggest the following:
Library initiates OTA transfer stream and transmit all FW for storage in external flash. Both sender and transmitter calculates some checksum of the FW and the checksum is sent finally, as a separate command.
The stream data is sent with a special command that bypasses signature. The checksum is sent with a type that is included with other signed types (currently only the singing handshake commands are excluded from signing).
That way, if receiver require it, FOTA will also be signed since the checksum packet is signed.
If the receiver accepts the signature (and the checksum is valid) receiver writes the bootloader specific indicators and restarts, so bootloader can transfer the received firmware to PROGMEM, and "Bob's your uncle". Secure FOTA to your difficult-to-reach node somewhere in the house

[tbowmo]

@hek said:

Neither of us have the flash memory though

Hmm we should do something about that at som point in time

I could send you a couple of bare boards, you could practice your soldering skils on ?

[tbowmo]

@hek said:

Neither of us have the flash memory though

Maybe we could figure something out.. I could send a couple of empty rev. 2 boards, and you could practice your soldering skills and assemble one yourself

[hek]

That might be a good idea. Just hope I won't mess it up too much. Which components do I have to order in the meantime.

[tbowmo]

@hek

I have a BOM at mouser, but need to double check it.. (Also, might have some of the capacitors/resistors in my "private" stock, so you don't need to order them)

[blacey]

@tbowmo you can sign me up too however I can handle the component side of it if you share the mouser BOM.

[tbowmo]

@blacey said:

@tbowmo you can sign me up too however I can handle the component side of it if you share the mouser BOM.

The BOM should be available at
http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=a509f9ca59

It should match the current PCB layout for the major number of parts. I haven't looked at the crystal yet, to see if that fits, as I have changed the footprint to the one provided by the manufacturer in china when going with rev. 2.

At the moment I'm considering if the crystal should be dropped from the BOM, kind of missing a real purpose for it at the moment, as I don't think that "precise timing" is necessary for a node that repports in at a regular interval.. I (for one) don't care if it reports temperature / humidity "exactly" every 60 seconds, or if it's every 55 or 65 seconds.. But others might have another priority?

Schematics / PCB layout is available on github : https://github.com/tbowmo/MySensorMicro (please double check BOM from mouser, and the eagle files. I might have missed something :))

[blacey]

@tbowmo Awesome! I'm on it

[tbowmo]

So, a small update on the rev.2 board status.

I am verifying the rest of the board now, before we kick of an initial testrun of 5 boards at the manufacturer. Everything seems to be working, electrically..

Unfortunately something has happened in the SPI library in arduino, so the external flash, is now crashing the arduino sketch, while initializing. Someone else has already reported it to lowpowerlabs github repo https://github.com/LowPowerLab/SPIFlash/issues/8

Having had the above issues, I have already build, and disassembled two nodes, trying to debug things :s

Oh the fun of debugging embedded things...

update

I found a solution, someone else had made the necessary changes to lowpowerlabs spiflash library (check the issue comments in the link above)

I also read in the release notes for arduino 1.6.0, that they have changed the SPI library to support transactions. Will this have any effect on MySensors? (@hek, any comments?)

[sharath krishna]

@tbowmo : if the connections are fine when can we expect he board for production ?? looks everything is fine

[tbowmo]

@sharath-krishna

We are getting closer to a launch. A production partner has been found. All on-board hardware have been verified as OK! And I'm verifying the last bits (Want to have a complete node running, before giving a GO..) Also finishing the software that should be preloaded on the atmega.

Depending on how things are going, we should be able to make the first trial batch within the next couple of weeks (I hope!) which we then need to verify before starting the big machine.

Going to be an exiting spring this year

[doblanch]

To where will you be able to ship the nodes ? I live in France. I don't know where you are located...

[hek]

@doblanch

It will be shipped directly from the producer to any location.

[doblanch]

@hek Thank you for your reply. I'm going to deploy may be like 5/6 nodes. Another question, By any chance, did you think about a case which accept module+battery ?

[hek]

A case already was on my short-list and we could very well provide it.

Depending on demand it could be 3d-printed or for larger quantities done with mold injection by our partner.

But I would really need some help from a (talented) 3d modeller for this. Do we have anyone here that can help out?

The box must have a battery compartment for 2XAA. A big question is if it also should have space for an extra sensor?
Would be great if we could provide a couple of cover-options for things like motion (HC-SR501) and another for light/uv/ir sensor. Hope we can get creative together here.

[tbowmo]

A small update from the workbench here

The first rev.2 node is transmitting like it has never done anything else right now.

Next up is programming the bootloader, I am having some troubles in that area.. It seems that it is programmed, but I can't get it to accept any downloads from the arduino IDE.

Anyone got any hints for me to follow?

[Anticimex]

@tbowmo have you checked that the fuse configuration matches the HW with respect to frequencies and such?

[tbowmo]

@Anticimex

I have checked, and double checked fuses I'm using avrdude to program the bootloader directly, and it seems that it is starting up (the LED is lighting up as it is supposed to). Also when I program a sketch via ISP (using jtagice3) serial is working fine, so it seems that fuse settings is right for oscillator (at least)

But I might have missed something with the fuse settings.

I get these fuses
AVRDUDE -U lfuse:w:0xE2:m -U hfuse:w:0xDA:m -U efuse:w:0xFE:m -U lock:w:0xFF:m

from http://eleccelerator.com/fusecalc/fusecalc.php?chip=atmega328p&LOW=E2&HIGH=DA&EXTENDED=FE&LOCKBIT=FF

[Anticimex]

@tbowmo I am just taking wild guesses and the one thing that came to my mind if you seem to have bootloader running but cannot download is that the serial line is out of sync for some reason. But I have not dissected the arduino bootloader or the protocol so I am in deep murky waters making assumptions now

[tbowmo]

@Anticimex

Yeah, but it's hard to debug things in the bootloader.

[Anticimex]

@tbowmo Tell me about it. It's what I do for a living
You don't have means to pick up the serial line after the FTDI adapter by any chance? It perhaps reveals garbage or signs of non-matching BAUD rates.

[tekka]

@tbowmo

The fuse settings say 8Mhz internal, 2kb bootloader. Which bootloader are you using and did you adjust the baud settings in the boards.txt for the IDE (i.e. upload.speed=57600)? Also, do you get serial output at the set baud rate when uploading a simple serial output sketch via isp? Alternatively, I recommend recompiling the bootloader at 8Mhz for correct baud settings.

[tbowmo]

@tekka

It's DualOptiboot that I'm using, compiled for 8Mhz (internal RC oscillator).

[doblanch]

@hek Hello, I have a friend who is working with 3D modeling. i can study it. I do not guaranty for the moment, as it doesn't rely on me directly. however I can do the best, and try to move forward.
If I understand correctly, we need the place for the sensor+antenna+AA battery...
On the PCB, is there some hole to place some screws ?
How should we close the case ? by putting some screw or just putting a cover ? make sense ?

[hek]

@doblanch

The board has humidity/temperature build in. So we only need space for maybe one extra sensor (question is how large volume this would need?).
Punch out holes for wires to external things like permanent power, buttons or reed-switches.

Click on cover would be nice but requires more accuracy in the making. A screw wouldn't be a big problem.

Many variables...

[tbowmo]

@tekka @Anticimex

Bootloader is working now.. I tried to compile for another target, atmega328_pro8, which worked.. (used "pro8" the other day, which also compiles for atmega328.. Hmm.. go figure)

[doblanch]

@hek I know , yes for the T/H sensor. As we put 2 AA battery, we have to know if we want to stack sensor/battery or not...otherwise, battery and sensor will be on the same plan.
I think that we can start without extra sensor, and add it in function of request, I'm going to buy a 3D printer, It will be my first tests.

[tbowmo]

Today the production files have been sent off to China, for the first batch of 5 prototypes build by them. We then need to verify them, and if they are found OK, we start a larger production run.

Feeling like Christmas is comming up

[markusand]

I'm too late for my suggestion, but maybe it can be implemented in future versions if considered. Just in order to simplify connectivity with sensors, spare pins could be accessible via grove connectors. However the board looks amazingly small!

[Ivan Z]

Why do not use CR123A accumulator?
It is smaller and can be charged.
And not nide regulator

I use box with charger. With CR123A accumulator.
http://www.ebay.com/itm/2600Mah-USB-Portable-External-Battery-Charger-Power-Bank-for-Cell-Mobile-Phone-/301514424642?pt=LH_DefaultDomain_0&var=&hash=item4633a90142

Very cheap

[jendrush]

@Ivan-Z Really nice idea for battery powered nodes:)

[korttoma]

@Ivan-Z how did you connect the power to the arduino? How are you powering the Radio? Is it a Pro Mini 3.3V? How long does the battery last? Did you do anything special to the arduino ( hardware changes or something else? )

[Ivan Z]

CR123A in full charge has 4.07v

Gas counter started 2014/11/01.

In winter, temperatures drop below -10

[tbowmo]

@Ivan-Z

You say that it don't need a regulator? the battery voltage is 4.07 when fully charged, that is 0.47V above the absolute maximum rating of the NRF24L01+, as it's only rated to 3.6V maximum. Same goes for the Si7021, maximum supply voltage is 3.6V.

So CR123A is not a good battery, unless you put a regulator in the loop, which then again uses current, and causes a voltage drop from battery supply

[Ivan Z]

DHT22 = 3.3-6V DC

CR123A = 3.6v ( Bat full charge i have 4.07v )

NRF24L01+ = 3.6

I have 8 device and his work with CR123A for 6 months
When charge some device cannot translate packets, but after work

[AWI]

@Ivan-Z I think you are lucky... I burned a few radio's with a similar setup (with LiPO solar charger) I like your minimal design. If you replace the DHT sensor with a htu21 you can make it even smaller. There are a few htu21d boards with a 3.3v regulator on it which you could use to power the radio.

[Ivan Z]

@AWI
What regulator do you use?

I do not use the regulator because it has a extremeconsumption
AMS1117-3.3 = 5~10mV in idle

[AWI]

@Ivan-Z I use the XC6206 series regulator. most of the times. The quiescent current for this one is very low 1-3 uA. This regulator is used by many of the sensor board suppliers to supply sensors with 3.3v Eg. In many cases (eg Adafruit) you can use the board as a "3.3v power supply"

[Roberto Brunialti]

Hi guys. I'm waiting for your board!
the only concern is about the 2xAA batteries adoption that could increase the overall size of a sensor node to a "normal node" size ( http://www.seeedstudio.com/depot/s/devduino.html?search_in_description=0).
I would like a stack as following: battery+board+radio. with the same footprint of the radio module.
The battery could be a CR123 with regulator, and the holder could be a pcb holder as this: http://www.memoryprotectiondevices.com/datasheets/BH-CR2-PC-datasheet.pdf
I actually ordered some of these: http://www.elecrow.com/devduino-sensor-node-v4-atmega-328-p-1201.html, at this moment the closest to my size requirements.
What do you think.?

[AWI]

@Roberto-Brunialti I am looking forward to this board also. I deployed a few Devduino V4's. These are really well built but lack the "minimal" size, have only a few connectors (enough in most cases as a good temp/hum sensor is on board).. And "restrict" you to the use of non-rechargable CR123 cells (3V,no regulator). I will love the very small footprint combined with the flexibility in power sources (and extra features) in the "Minimal design thoughts" design.

[tbowmo]

Think we should rename the thread to "Mysensors Micro" as this is the new name, since it's the first "official" board from mysensors.

Anyway, just got a couple of pictures from the factory in China, they have build the first batch of 5 pcb's that they are verifying at the moment, and then they should be shipped to us (either @hek or me?) and then we need to verify it, before giving a go on the production.

So we are comming closer to a "launch" of the device.

[hek]

@tbowmo

Yep, might also be good to create a new thread in Announcement when it has been launched (and is for sale) with a back-reference here for history/design decisions made by you.

I should probably start working on a more complete page on the main site with more details and illustrations.

[Tibus]

In your design, C3, the nrf 4u7 capacitor, is a classic ceramic capacitor. In the mysensors tutorial, they write a polarized capacitor is better for the NRF. I use tantalum capacitor wich are bigger but is there a difference with the ceramic one for the nrf. I would like to use a ceramic 0603 too if there is no difference for nrf.

Thank's

[tbowmo]

@Tibus

In theory ceramic capacitors should be better, it has a lower ESR, and are better suited to reduce ripple, or noise on the supply locally, as it has a faster response to power requirements, than equivalent electrolytic capacitors.

[Mickey]

will it be possible to use this board pcb without soldering the sensor , flash and security chip?

[tbowmo]

@Mickey

Yes, you can use it without those mounted. But I don't think that we are going to sell it without those components mounted

[Roberto Brunialti]

Any good news about the d-day (delivery day ) ?

[hek]

Small production run of 200 units started this morning.

[Mickey]

@hek said:

Small production run of 200 units started this morning.

You would run-out of units very soon...

[Roberto Brunialti]

when preorders will be available ?

[hek]

@Roberto-Brunialti

I will check with Itead Studio if their shop can handle pre-orders.

[tbowmo]

@Mickey

Then we will make another 200 (or more, depending on requests)

[hautomate]

What's the expected price point for these?

[tbowmo]

@hautomate

They are going for 14$ plus shipping.. Expected shipping date is set to 20th of May.

(the project is receiving about 1$ for each unit sold)

/ Thomas

[gadu]

Oh! Where do I order?! Been waiting for this!

[tbowmo]

@gadu

An initial product page is up at iteadstudio : http://imall.iteadstudio.com/mysensors-micro.html

We are working on updating product description etc.

[Dwalt]

FYI - ITead is already taking preorders for the board.

[Roberto Brunialti]

Hi, I have ordered some boards from Itead. Just some doubts: is the board a 5v or a 3.3? what's about nrf24 decoupling capacitor? May I assume the nrf24 is correctly powered at 3.3 V by the board?
Sorry but i'm on the "soft" side more than the "hard" ...:-)

[Anticimex]

@Roberto-Brunialti The board is "2XAA" battery, in other words; 3V. Some components on the board won't survive 5V so it is important not to use that voltage. Decoupling for the radio is onboard.

[Anticimex]

The board has it's "own" thread as of now:
http://forum.mysensors.org/topic/1345/sensebender-micro

[Roberto Brunialti]

that ìs fine for me!

[Frank Herrmann]

Hi, i ordered some boards from OSHPark and at the weekend i solder this thing together. Here a pic from my work

Ok, it's work. You see, i have old nrf24 Modules they have not the same pinout, but i ordered some here in germany.

Some points to the design:

• this pcb has on both sides small SMD Components, that very hard to solder. I solder my one with an IR Oven and can only solder one side. It's mostly ok becouse on the second size i can solder with an iron, but never 04 components
• the size of smd components are too small, i understand this when you use the small Atemag328p MLF and only 04 components. Better are 0603 or 0805.

Ok, enough ... the board are great and give me a lot of ideas to my board. my are a small bigger but use the nrf24l01+ SMD version and a normal arduino pro mini. Please have a look:

[tbowmo]

@Frank-Herrmann

looks nice. And yes, I know that 0603 is prefered for home soldering. However, as we are going to get this SMD assembled in china, there is no problem in using 0402 components.

Also, if I where to use 0603 (or 0804 for that matter), the board would be bigger.

I am working on another pcb now (a GW for mysensors), where I am going for 0603, as I don't have the same size restrictions, as I had when doing this board. This will also be double sided (so far anyways, might change it down the road)

[magpern]

@tbowmo what type of capacitors do you use for the sensebender? The 100nf are ceramic I suppose, but what about the 4.7uf for radio?

[tbowmo]

@Magnus-Pernemark

It's all ceramics.. (also the 4.7uF for radio)