I want to buy an emontX pcb, and populate with minimum components - initially no sensors. I presume I can't buy this through the OpenEnergyMonitor shop (full kit or bare pcb seem to be the only options). If I buy the atmega328 from another supplier, do I have to specify anything special, such as bootloader? Anything else?
Yes those items can be purchased through the shop. All Atmega328's are supplies with the Arduino Uno bootloader ready loaded. We recommend this bootloader since it supports anti-crash watchdog resetting.
No further action other than assembling the units (see the build guides) and uploading code from the Arduino IDE is required.
All the best,
Sorry, not made myself very clear.
I've already build tx, glcd and base, which all came from the shop - all working except the base which is a bit unreliable uploading.
I now want to build a second tx, but I may not want any sensors. (My design keeps changing, so I'm not sure.) Via the shop I can only buy a full kit, which is potentially a waste of some components that I don't want, so was wondering how I could source the bits I need from elsewhere.
You can buy an atmega328 with arduino bootloader from wherever place you´d like. If you have an arduino and a protoboard, you can even buy an atmega328 and use the arduino to program the bootloader on the new chip.
The minimal components needed to run the 328 is a stable 3.3v or 5v power supply and a 10k resistor. (using 8 mhz internal oscillator). If you want 16mhz add a couple of capacitors and a crystal.
The RFM needs 3.3v, so better use arduino on that voltage to avoid aditional components.
look at the following links for more information:
PS: give some credit to the openEnergyMonitor shop and buy it with them...
Open-source tools for energy monitoring and analysis. This project uses the GNU General Public Licence