Minimal design thoughts

[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