What did you build today (Pictures) ?

[alexsh1]

Finally finished building my dual precision voltage reference LTC6655:

[alexsh1]

@acb I have built similar board.

The only downside is the cost and size of Atmega1284p is just so prohibitive. Yet it is 8 bits processor. I have only one fully conpleted board and a few blank pcbs.

[acb]

That looks awesome @alexsh1!

Nicely laid out and cleanly soldered. Was that with an iron or hot air (or both)? Nice clear silk too; I like the power and “signal” symbols. Did you ever try a FOTA update with it? Or a low power/speed profile?

I see you went a bit wider and longer than the standard Pro Mini, (I’m assuming) to get at all the pins and add the extra regulator, LEDs, etc.

I was constrained by needing something that fit the same footprint for existing boards I already had, e.g. other “motherboards” I’d made similar to @sundberg84’s excellent Easy/Newbie PCB or wanting pin-compatibility for stacking boards like the ATSHA+EEPROM+Radio+ICSP one below:

I tried routing with the chip at a 45 degree angle too but couldn’t get a DRC to pass with the pads so close to the PTHs. I may try again with shorter (custom) TQFP pads...

Re: 1284p’s downsides of cost and size.

I know. I ended up justifying it to myself this way:

We can all get cheap 328p Pro Minis from Ali for around $2. The vast majority of my Pro Mini projects are battery powered, so there’s some “labor cost” to disable the power LED and remove the regulator. But regardless, I certainly can’t make myself a low(er) power Pro Mini for $2 - the OSH Park PCB alone is probably close to that.

I think the cheapest I ever got 1284p chips for was around $2.50, again from Ali. My “Pro Mini XL” PCBs were around $1.70 from OSH Park, add a sprinkling of 0402s, etc. and we’re probably at around $5.

I couldn’t find any 1284p-based boards near that price. The closest I got was Kevin’s Mini Duino, which is another lovely looking board, but doesn’t fit my need for a Pro Mini-constrained size and pin-compatibility. Essentially, I was after something close to a drop-in replacement.

So, $2+ versus $5+ for all the benefits (at least as far as I was concerned) listed above? It became a bit of a no-brainer.

And on the low power front, I profiled the MySensors library sleep command on it at around 5uA on 4.5v @ 20MHz using an external full swing, around 4uA on 3v @ 8MHz and around 3uA on 1.8v @ 1MHz Internal RC Osc:

Those numbers are certainly good enough for all my current applications - no pun intended! ;)

But I would like to look at the 32-bit contenders as potential replacements.

I’ve seen nRF52s with 512K for around $2 on Ali, so maybe I’ll try my hand at a Pro Mini nRF52 or something similar eventually. The board above was a fun challenge, and afterall is what this is (mainly) about for me.

[dbemowsk]

@acb Nice pro mini sized 1284 boards. These would work nice in my in-wall OLED scene controller boards. The standard 328 pro minis really limit what I can do with the OLED display when using it with the MySensors library. I could get more use out of the graphics end of the display with something like that.

Do you have these on OpenHardware.io? Can fully functional boards be purchased somewhere? I would be interested in trying a few out if possible.

Kudos on the design.

[acb]

Thanks for the kudos, @dbemowsk. Right back at you for your scene controllers; I’m trying to get into 3D design myself, but can’t justify the time commitment right now.

Re: Do you have these on OpenHardware.io?

No, sorry, that would require me to be far more organized than I am at present! ;)

Maybe if there was enough interest, I could justify putting in the time to clean things up enough to publish… But it is valentines today, so any tinkering will surely be met with an icy stare if I try it tonight! :o

Re: Can fully functional boards be purchased somewhere? I would be interested in trying a few out if possible.

Really? I’ve never done something like that before. You do realize these are very much “alpha” right? I mean, I’ve tested the majority of the pins, but nothing like proper production hardware verification or anything. Having said that, it’s not like there’s anything complicated going on.

I managed to dig out four spares this afternoon that I’m not using from the last batch I made - how many would you like?

Three have a 1284p attached and one has the regular 1284 - I believe the only difference is the 1284 doesn’t have BOD, but I normally turn that off anyway for a (probably) miniscule power saving. I haven’t installed the crystal oscillator or reset switch yet. I don’t normally do that until I know what the use-case is. I believe I have enough spare 16MHz and 20MHz ones to fit (maybe some 8s) and some SMD reset switches too.

The only other thing would be the bootloader. I could flash the standard MySensors DualOptiboot?

So, if you (or I suppose anyone else for that matter) are interested, just shoot me a chat message via my profile and we can figure things out off-thread, as this is a bit off-topic now.

Thanks again for the interest - even if you don’t buy - made my day! :)

[kalina]

Some photos of my new device - MDMSPanel "Nextion". I have finished soldering an hour ago)) Next week i will public this project.

[bjacobse]

@kalina
Looks good, however due to EMC I strongly recommend to add a GND groundplane on your PCB. I would myself have TOP layer as +DC and BOT layer as GND, this provide less power "sparks" on the tracks and a "capacitor" effect on whole PCB

https://en.wikipedia.org/wiki/Ground_plane#/media/File:TerraTec_G3_circuit_board_2.jpg

https://www.quora.com/What-is-the-importance-of-a-ground-plane-of-a-PCB?share=1

[mfalkvidd]

@kalina very cool board. Must be your most advanced MySensors board so far?

[kalina]

@mfalkvidd I would to say what this board is the most necessary for me at the moment. I tired of using various gadgets as a control panels for my nodes. Also, i want to try RS-485 in conjunction with MySensors. Next step is add RS-485 to my MDMSGate....

[monte]

@bjacobse to do proper ground and vcc planes you need a 4-layer PCB. Otherwise you won't get much of a difference in terms of EMI. Another way is to have 2 layer board and to have one layer only for ground plane, but that means you have to do all routing on one side, without making lines across your ground plane. Otherwise you decreasing grounding effect on EMI.
More on this topic in this free webinar: https://www.signalintegrityjournal.com/events/54-best-iot-board-design-practices-balancing-density-cost-low-power-and-mixed-signal

[bjacobse]

@monte
Well now Kalina already uses 2 layer PCB, so to improve current 2-layer PCB with ground planes are strongly advised.
Yes 4 layer is naturally much better, but is it needed for a "commodity" device? I think not, and it will increase PCB cost...

If you don't have a GND and power planes, you will most likely have power spikes when an IC needs current, this will introduce a magnetic field that will "disturb" especially sensitive analogue tracks and clock signals

[FotoFieber]

My actual project is a doorbell sensor with additional temperature and humidity sensors. Tried different ways to detect the ring:

• hall sensor (failed)
• microphone (FFT, ongoing research)
• optocoupler to detect the 12V AC -> favorite solution

As I was heavy prototyping, I tried wire wrapping and it is fun:

[alexsh1]

@acb Hot air has been used for soldering the board. I have not tried low power as I did not build this board for a battery sensor. My board has got two LEDs - power and another LED connected to D0 so clearly not very low power. I also have a 16Mhz firmware. I did not have any size limitation either. I have one particular node with a few sensors and with signing I cannot upload the sketch onto ATMEGA328P as it is marginally larger. Having said that I have not spent too much time optimising the sketch. I think that refactoring libraries, you are fine with ATMEGA328P in 98% of all MySensors applications.
BTW - this is not my project. I have followed it https://github.com/peekpt/mightyduino

Re cost. I stopped Ali shopping for ICs and other sensitive components some time ago after purchasing some fake ATMEGA328P and wasting so many hours trying to troubleshoot it. There is a post about it here on MySensors forum. Ever since I order all components on digi-key. 1284p is priced around $5 + 20% VAT. 328P is priced at $1.2 + VAT. However, I can also buy ATSAMD21 for $2.2 + VAT. Do you see my point? 1284p is extremely expensive and yet it is still 8 bit processor. That's why for me it was a one-off board.

Re sleeping
I am using TPL5110 which I built myself (similar to Adafruit one).
Check out sleeping current:

Sadly, I struggled to get some sensors to sleep properly - probably lack of my programming skills - and with a sleeping current being hundreds of uA, I had to resort to this trick. Most of the time, the node sleeps is disconnected from power by TPL5110 then timer is up and it powers up, sends all sensors readings to the GW and then power gets disconnected to the node, only TPL5110 goes to nA sleep. Perfect!

[alexsh1]

@kalina scene controller? I have almost finished mine on Nextion, but do not have time to tidy things up.

[kalina]

@alexsh1 Yes, it will be a scene controller. I also developed nice enclosure with a magnetic mount. In a few days I will share new photos.

[monte]

@bjacobse but it actually seems that he HAS a ground plane on one side of PCB, if you look closer at the third photo ;)

[bjacobse]

@monte I didn't notice this, but you are right, "hidden" LCD :-)

[bjacobse]

@fotofieber
Wirewrapping is an "old" and well proven technology, remember to have extra cable in case you need to re-wire your cables. Not so popular by DIY as tools used to be fairly expensive as it was protected by patents...

[bjacobse]

@bjacobse
Just to add a little more info about adding a GND plane to your PCB
I work in a electronic company, not doing PCB layout there though.
but we have a TV adapter which have 2.4GHz transmitter. and this PCB is GND on both sides and with plenty GND via's (all the small holes) to ensure good grounding

In case you wonder what it is, then it's an Oticon TV adapter 3.0
https://www.youtube.com/watch?v=r4bTIQPdCEo

[alowhum]

A picture from the touch screen version of the universal 433Mhz signal cloner.