rapid decline of moteino supply voltage its lower values..

[perky]

The MCP1703A though is specified for input voltages below the regulation voltage, the MCP1703 may well be the same silicon or based on the same circuitry. In fact it shows a graph of ground current versus input voltage, and 'dropout current'. Basically the pass FET is fully on but has a resistance, it's that resistance that defines the dropout voltage at full current.

The current taken here though is an order of magnitude greater than what might be expected, and is consistent with what you'd expect if two logic outputs were driving each other at opposite logic levels. I'm convinced the radio and flash devices are both seeing their chip selects low because the BOD has tri-stated them, and therefore turning on their drivers, and are driving MISO at opposite logic levels.

Mark.

[john4444]

Hi Perky,

I stand corrected.
I had just looked over the datasheet and did not see any spec or graph of current below the regulation voltage.
Thanks for the correction.

[perky]

Thanks Perky I'd definitely want to try that but I don't know how to do it. Could you please tell me or possibly guide me what and where (in the sketch) I can add the line of code? FYI: Attached is the node sketch I'm using for this test (almost same as Node example from library).

The BOD level is set by the fuses, I don't think there is a way to do this in software. You might try adding a 10k resistor pullup to one of radio or flash CS# signals if you can't do this (actually the radio is probably better, the flash behaviour isn't defined below 3V, that would prevent the radio MISO buffer turning on).

Mark.

[TomWS]

IMO, you guys are wasting your breath trying to explain the behavior of a system that is operating outside of spec (don't know what BOD settings are, processor is 16MHz and already out of spec by 3V, etc. etc.).   And to what end?  Clearly the system won't work at that voltage.  Design the system to maintain the voltage above operating level or totally shutdown below that.

Tom

[Felix]

IMO, you guys are wasting your breath trying to explain the behavior of a system that is operating outside of spec (don't know what BOD settings are, processor is 16MHz and already out of spec by 3V, etc. etc.).   And to what end?  Clearly the system won't work at that voltage.  Design the system to maintain the voltage above operating level or totally shutdown below that.

Totally, the initial question was WHY IS THIS HAPPENING below 2.8V and the answer is clearly because of the BOD reset state. Whatever low power state the MCU is in, once it gets below the BOD it will not be low power anymore.

And watching that video of the discharge, even so the 25F total capacitance seems way way too fast discharging. The humble 7.5F setup I use can keep the mote going for days without any charging from the small solar cell, before entering the BOM reset of doom and draining to death.

[perky]

The reset current is specified, which is about 750uA. That's all it should be taking (maybe a tiny bit extra for the BOD, but no clock is running). This is still an order of magnitude at least below what is being seen. My money is still on MISO...

Mark.

[SanG]

The rapidly declining voltage may be caused by the increased current consumption of the voltage regulator.
Even low current draw regulators consume much more current when the input voltage drops below the min regulation voltage.
The MCP1703 (on the Moteino) operating current is not defined below 3v.

Yes that makes sense, regulator draws relatively more current at voltages lower than it is supposed to operate ..Thank you for the insight john4444

The BOD level is set by the fuses, I don't think there is a way to do this in software. You might try adding a 10k resistor pullup to one of radio or flash CS# signals if you can't do this (actually the radio is probably better, the flash behaviour isn't defined below 3V, that would prevent the radio MISO buffer turning on)

Totally, the initial question was WHY IS THIS HAPPENING below 2.8V and the answer is clearly because of the BOD reset state.

Now I know it's the BOD level set internally and possibly I can't do anything to change it..Thank you Perky and Felix

Design the system to maintain the voltage above operating level or totally shutdown below that.

I was and am still trying to do it. Thank you Tom for the short and straightforward suggestion

And watching that video of the discharge, even so the 25F total capacitance seems way way too fast discharging. The humble 7.5F setup I use can keep the mote going for days without any charging from the small solar cell, before entering the BOM reset of doom and draining to death

Very keen observation Felix..yes the Scaps in the video indeed are discharging much faster than they are supposed to even above 2.871V, that's because the sketch is the "Node example" sketch from RFM69 library whose transmit period has been changed to 10s, no sleep feature implemented. My actual circuit (attached earlier) consumes much smaller current (Scaps discharge much slowly).

Anyway, I got my answer and I will see what I can do to my circuit to fix this issue. Thank you so much all for helping me out.

[TomWS]

Now I know it's the BOD level set internally and possibly I can't do anything to change it..

You can change the fuse settings on a Moteino.  If you get an ISP programmer that has a breakout board for the programming pins, you have access to all the necessary pins on the Moteino headers.  You will have to add pullups on the Radio SS (pin D10) and, if you have the Flash chip on board, to that SS as well (pin D8).  Finally, make sure your programming voltage is compatible with the components on the Moteino board (3.3V).

I've reprogrammed the Moteino to change BOD, change to 8MHz internal, and to replace the Bootloader.  Easy peasy.

Tom

[SanG]

I will try that Tom.

Thank you.