Moteino input voltage

[Roger2016]

One of my projects it to mount a Moteino in my shed to monitor and control a couple of things out there.  The shed is solar/battery powered and my charge controller puts out as much as 15.5 volts (in equalization mode).  The specs on the Moteino state up to 16 volts, but 12 volts is recommended.   Do you think it's safe to hook the Moteino directly to this solar/battery combo given i'm so close to the max input voltage or should I regulate the input voltage somehow perhaps with a 7812?

This is the solar charge controller I'm using.
https://www.renogy.com/template/files/Manuals/20A-30A-40A-MPPT-Solar-Charge-Controller-Manual.pdf

Thanks!

[Felix]

The MCP1703 says 16v, I would not really put it to an effort to bring 16v down to 3.3v, especially if that's a constant or often occurrence.
If it's just occasional transients of 15v+ then I would use a TVS like this.
Otherwise I'd probably use a hefty 7812, 7809 just to be nice to the Moteino

[TomWS]

Depending on how low the Solar Battery puts out, a simple 1W Zener diode will drop the voltage a few volts into your safe region.   Even one or two 1N4001 diodes will get you there.

Tom

[Roger2016]

Hi Felix,
What's the amp draw on a moteino?
I see you used a Murata OKI-78SR-5/1.5-W36-C http://www.digikey.com/product-search/en?KeyWords=811-2196-5-ND on your Doorbell monitor stating it was more efficient than a linear regulator.  Would this be a good choice?

[Felix]

Amp draw?
It depends how you use it.
MCU active will be ~15mA, radio will add another 15mA in receive mode, up to 130mA while transmitting.
So tops 150mA.
Put in sleep mode it would go all the way down to ~6uA.

The OKI switching regulator is a great choice for bringing from up to 36v down to 5V.

[perky]

How much current with CPU active? 15mA seems a bit excessive! If you run at 3.3V at 8MHz it's more like 4mA I think.
Mark.

[Felix]

I was eyeballing based on past measurements but I think it's at least 10mA.

[steve v]

If I want to run my moteinos down below 2.85 volts to say 2.5 volts, currently it resets at 2.85 volts,   besides bypassing the regulator, do I need to do anything else ?

Should I program the BSOD fuse to 1.8V  using an AVR programmer ?

or does the command  "  LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF); "  disable the Brown out voltage select all together ?

[perky]

I was eyeballing based on past measurements but I think it's at least 10mA.

I think you may well have been measuring other things as well like IO current. According to Figure 35-5 on page 590 the active supply current of a ATmega328P at 3.3V and 8MHz internal oscillator is about 3.5mA, add a few hundred uAs for any peripherals and it's typically about 4mA. I think 10mA is over-estimating it.

[TomWS]

If I want to run my moteinos down below 2.85 volts to say 2.5 volts, currently it resets at 2.85 volts,   besides bypassing the regulator, do I need to do anything else ?

Should I program the BOD fuse to 1.8V  using an AVR programmer ?

Yes, or disable BOD entirely.

or does the command  "  LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF); "  disable the Brown out voltage select all together ?

No, it only disables BOD while you're sleeping for the 8 seconds.

Tom