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By gDFfRc7VvzfYydHP
#222111
I would like to do some "quite low power" prototyping and hand-made small production for a project. This means that I would like to:

- have access to all my usual pins as a development board

- have no power or other LED that is on by default (user-controlled LEDs for debugging / playing around are fine and even desired)

- be able to power from USB / jack during development if I want, which implies having a power regulator and possibly polarity inversion protection on board, but also being able to bypass them altogether (i.e. the usual 3.3V rail, this is already well available)

- be able to both use USB for programming when a USB cable is plugged in, but bypass altogether and do not power the USB interface chip when there is no USB cable

- generally, have a board that, when not plugged in a USB or jack for power, minimizes power wastes

My questions are:

- is such a board available (I don't think so, can you confirm?)

- how far is the RedBoard from fulfilling these requirements? In particular, if I desolder the power LED, and if I feed 3.3V directly through the 3.3V pin:

-- can you confirm that the power regulator is bypassed altogether (I would guess so)

-- is the USB interface chip also bypassed / powered down altogether, or are there some power losses there?

-- any other sources of losses I should be aware of?
User avatar
By TS-Chris
#222211
It doesn't look like we have a board that checks all of your boxes, but a good compromise would be our Artemis Nano.

You might have to remove an LED or possibly cut a trace but it's the closest thing to what you're after.
By jremington
#222217
It is very simple to use the tip of a hot solder pencil to "swipe" off unwanted LEDs, voltage regulators, etc. from any board. I do this with the Pro Mini, for example, and easily achieve the 100 nA power down sleep current possible for a completely bare bones AVR-based Arduino. It takes just a couple of seconds to do the surgery.

Be aware that fake Atmel processors are being found on some of the newer cheap clones, and one sign of this is power down sleep current about 1000x too high. See https://hackaday.com/2020/09/15/deep-sl ... some-chip/
User avatar
By gDFfRc7VvzfYydHP
#222238
Thanks for the tips! :)

I agree this can be fixed "by hand", but this is an extra step. In my "business" (building equipment at University, in a department without electrical engineering background, I work with applied mathematicians), we have many students / faculty members who have no experience / no interest to learn / are afraid of doing this kind of LED removal, so our lives would be easier with such a board that is low power off-the-shelves :) .
User avatar
By gDFfRc7VvzfYydHP
#222250
I have designed (and got produced by Seeed studios) some custom PCBs with bare bone ATmega328P and other low power components on them in the past. It works well, but it is not the use case I have now. I want something simpler, out of the box.

I was thinking about this tonight and I wonder if it would be possible to have a "simple" solution like adding a DIP switch in this kind to the boards produced: https://www.sparkfun.com/products/8034 . This could also provide a few user-controllable inputs, which is always nice, for example:

Something like:

- 1 switch is used to switch on / off the power LED
- 1 switch is used to switch on / off the power to the Serial-UART converter, so that it can actually be disconnected completely to save power if wanted. To make it clear of its powering state, consider adding a LED indicating "Serial-UART converter power"
- 1 switch is used to provide on / off power to the serial TX and RX LEDs. I.e., if the switch is off, the LEDs will never light, if it is on, it will light as we are used to
- 5 remaining switches could be wired to some "pure digital" MCU inputs. Something like switch off is floating pin, switch on is pulling up the MCU pin

Anything more I forgot that could gain from being on an on off switch?

What do you think? It should be very inexpensive to add, and would make everyone happy - the guys who want low power can get it by toogling a few switches, the guys who want lots of lights for debug get it too, and we win a few inputs for user applications.
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