mikew67
commented
4 years ago Doing a bit of reverse engineering, the Moddable Two uses a CJT1117B-33 LDO, which is rated at 1A output, fixed 3.3vdc, with a drop out of 1.15v at 1A. With the Balls demo running as a sample load, the board consumes about 140ma. USB 2 is spec'd to provide 0.5A at 5vdc. So with a comparable supply, it looks like there should be plenty of power available at the 3.3v output pin to run my peripherals (something between 500-140 = 360ma, or more if the power input can handle >500ma. Ultimate limit would be the 1A rating of the LDO (or less, based on heat dissipation).
That's all good, but the 1.15v drop out of the LDO means a single LiPo cell wouldn't suffice because the voltage out of the LDO would be too low (4.15..3.75 - 1.15 = 3.15..2.60) and unregulated. Two LiPo cells in series should work just fine (i.e., ~7vdc input) as long as all the components upstream from the LDO can handle it.
Will try some experiments, at least at the low voltage end...
chris-moddable
phoddie
I note that in issue #221, a request for schematics for your hardware products was denied. OK, but I do need External Interface Specs for your products, especially the Moddable Two. I intend to build some daughter cards for the MTwo (R6, in the current case), and run it off battery power. Hence, I need these specs, including:
6-pin input programming connector, including its voltage limits and signal characteristics. For example, if I supply battery power to the +5v input pin, what's the lowest possible voltage? (Something a single LiPo cell can supply, 3.7-4.1v.). Presuming the internals of the board are all running at 3.3v (LCD, too?), can I supply a filtered 3.3v to some internal point.
20-pin external connector, including the same info. Suspect most of the signal pins are direct connects to the ESP32 pins, so I can take the electrical specs from the ESP32 datasheet, but there are a few additional questions, e.g., what's the current capability of the 3.3v output? How is it filtered? Is there any significant capacitance on the SCL and SDA lines (need to know when I'm pushing I2C interfaces at the chip's max speed).
Part number for the mating 6-pin and 20-pin connectors would be useful, too.
Anything else you can add about the HW and electrical specs.
Thanks,
Mike