Which ATmega do i go with?

[Samuel235]

@tbowmo - I was only having the temp sensor there in case of a irrational/unpredicted sense of events and causes a fire, hoping my theory would make this board over the top safe. However if you feel that there would be no chance what so ever of this happening i will not bother using it.

On the chip front, would i be better using something smaller/less power hungry since i'm only using a switch and the radio here? I'll stick with the 328-PU if there isn't much power i can reduce it by.

@scalz - Indeed, like i have said before, i love the look of your 'MyTinyCamel' board. I also love the idea of your sensor board in the wall too, this will be my next application, however I wanted to design this for the cases where you are very limited on space inside of your wall socket and just needed a switch node. I can only hope to develop our products together at some point in the future ;)

[scalz]

:sunglasses:
for the chip, I agree with tbowmo. you should use 328p I think. p for picopower (140-200nA max sleeping, on standalone), widely arduino and mysensors used. enough mem to handle mysensors lib, radio..no big surprise.

[tbowmo]

@samuel235

Go with 328p.. you'll only get more problems, if you choose other chips (like the attiny mcus)

328 is the standard for arduino. Just be sure that you have access to programming (ISP port) pins on the mcu, otherwise you'll have problems in putting in the bootloader.

[Mickey]

@tbowmo said:

You don't need the crystal, there is an internal 8mhz RC oscillator available.

I would recommend to take a look at the sensebender, it's as basic as it can be (just remove sensor / flash / atsha204 if you don't need those)

How do you programme a factory atmega328p to run on 8mhz internal?

[Samuel235]

Right, okay. So 328-PU it is. By the way just to let you know i was looking at the likes of the ATmega8, and others in the mega range. Wasn't bothering with the ATtiny range. But i'll stick with ATmega328-PU. But other than the chip, rf24, the switch and a serial connection for uploading the bootloader and sketch, i don't need anything else to have a functioning 'arduino', right?

Ill get some more design and schematic work done when i get home from work tonight and get some drafts up on here.

[Samuel235]

@Mickey said:

@tbowmo said:

You don't need the crystal, there is an internal 8mhz RC oscillator available.

I would recommend to take a look at the sensebender, it's as basic as it can be (just remove sensor / flash / atsha204 if you don't need those)

How do you programme a factory atmega328p to run on 8mhz internal?

I have the line of code in my documents at home somewhere, ill post them later if no body provides anything by then. If i can find them that is.

[tbowmo]

@Mickey

By default the atmega328p is running from the internal 8Mhz oscillator, but with clkdiv8 enabled, so that it runs at 1Mhz. For running it at 8Mhz you have to set the fuses and disable the clkdiv8. I'm using the following avrdude command to set fuses with my jtagice3 programmer in an atmega328p

avrdude -c jtag3isp -p m328p\
-U lfuse:w:0xE2:m \
-U hfuse:w:0xD2:m \
-U efuse:w:0xFE:m \
-U lock:w:0xEF:m 

change above to use the programmer that you have

[Mickey]

@tbowmo said:

@Mickey

By default the atmega328p is running from the internal 8Mhz oscillator, but with clkdiv8 enabled, so that it runs at 1Mhz. For running it at 8Mhz you have to set the fuses and disable the clkdiv8. I'm using the following avrdude command to set fuses with my jtagice3 programmer in an atmega328p

avrdude -c jtag3isp -p m328p\
-U lfuse:w:0xE2:m \
-U hfuse:w:0xD2:m \
-U efuse:w:0xFE:m \
-U lock:w:0xEF:m 

change above to use the programmer that you have

So if my current fuses are like this:

can I still communicate with the chip with usbasp without external crystal?

[Samuel235]

@tbowmo said:

Now for the external flash, and bootloader support. There are two bootloaders available for OTA FW upgrades.

• MysBootloader - no external flash needed, but only supports NRF24, and no security features (signing etc.)
• DualOptiboot - needs external flash to store fw while uploading it. Supporting both NRF24 and RFM69 radios, and supports signing (dev branch of Mysensors library is probably needed)

Without using external flash could i use the Arduino bootloader? Did you only mention these 2 for their "OTA Firmware upgrade" ability? I'm struggling to workout how to burn this MysBootloader onto my chip. I can't find much information on this.

EDIT: So, I've been reading on the Google Docs for bootloading, and it would appear all that i have to do is put the MysBootloader sub-folder into the bootloaders folder in my Arduino IDE documents. So, i have done that but i still only have "Burn Bootloader" in the tools drop down menu, is this normal not to be able to choose which bootloader i would like to burn or do i need to have my board plugged into my computer to then be recognised to be able to burn MYSBootloader?

[Samuel235]

And which way is your/the preferred method of burning the bootloader, would you use a Arduino Uno and burn the bootloader using the "Arduino as ISP" option or would you go with something like a USBtinyISP adapter? Could you provide a link for a specific programmer if you use one as I'm seeing a lot of varying types/sizes/shapes and I'de like a recommendation of a working device from someone that uses one. If you use an Arduino UNO, i will just purchase one of those instead.

[tekka]

@samuel235 Please follow these instructions for burning MYSBootloader and testing OTA updates with MYSController. Both, USBasp and ArudinoISP are easy to use as long as you do not mix up the cables...

[Samuel235]

@tekka - How on earth did i not stumble across this! Thank you very much! I will get ordering myself an UNO in preperation to getting my board manufactured. Now i know which connections are needed in my ISP header, i will carry on sketching out the schematic. Thank you once again!

[tbowmo]

@samuel235

I'm using genuine atmel programmers (currently I'm on jtagice3) been serving me fine for the last couple of years (also have the added benefits of being able to work together with gdb, so I can debug arduino code on my atmel sam D21 mcu)

Anyways, there are lot's of (cheaper) programmers out there, amongst others you could use another arduino as programmer..