Hello!
I am designing an awesome board that I am excited to share, but I have a few “fundamentals” questions I’d like to ask.
For starters, I want to use the RTC capability of the Artemis. I played around with the example script using my Redboard, and it looks/works awesome!
In my application, I have 2 18650 batteries… I have battery → load switch → 5v regulator → 3.3v regulator.
But I want the RTC to remain running when the load switch is off. So I have another very low power 3.3v regulator that is always on… basically to act like a CR2032 coin cell. Then I started to worry that I don’t have bypass-diodes over my switched regulators and that could cause damage. I reviewed the Redboard Schematic, and it doesn’t appear you guys used bypass diodes though… Do I not need them?
https://cdn.sparkfun.com/assets/4/5/a/3 … ematic.pdf
Edit: My apologies, this was supposed to be under “Sparkfun products using Artemis”
Sorry for the serial posts… I don’t see a way to edit previous posts.
Anyway, I didn’t know it but it looks like “reverse current & reverse voltage protection” is the key term I was looking for in my part selection for my switched on/off power rail. All is solved!
I’m so stoked to show off this project with the Artemis with the Sparkfun guys/gals. Stay tuned! (probably a few weeks).
More questions in-bound, soon enough 
I really want to make a video series for youtube on how to design with the Artemis, hopefully I can make that a reality. Anyways, getting ahead of myself…
Change of questions… If the Artemis had a Vbatt pin, this would be perfect for that. I don’t see one listed though. Do you know if any of the pins correlate to Vbat, that could take this always on 3.3v regulator?
Hi Rocky!
Your power solution sounds cool! By checking the schematic of two of our Apollo3 boards strongly suggests that the Apollo3 does not have a Vbatt pin. Our solution is to “OR” the voltage from the battery with the main supply voltage using low-drop diodes
https://cdn.sparkfun.com/assets/2/b/7/4 … ematic.pdf
https://cdn.sparkfun.com/assets/a/8/c/1 … is-ATP.pdf
You could do this:
2x18650 ----> load switch → 5v reg → 3v3 reg – diode -----> Apollo3 power
| |
→ lp 3v3reg → diode ------------------------------
But why have two 3v3 regulators? If you expect a lot of current draw on the 3v3 rail when in the “on” state then I could imagine doing this. However if your low-power 3v3 reg can supply enough current for the main operation then you might consider:
2x18650 ----> on/off switch → 5v reg → 5V devices onboard
|
→ lp 3v3 reg → Apollo3 power (always on) + 3v3 devices onboard
Oh - formatting gets messed up. Here are photos of my bad ascii representations of circuits placed inline
Thanks for the reply @liqud.soulder!
These are great suggestions, they OR supply would have worked great! I actually decided to omit a power switch all together, and have the 3v3 regulator (now a switching regulator instead of LDO), always on. I realized all my down-stream devices are operated from IC’s with EN pins, so I really didn’t need a power switch. I am hoping I can use the Apollo 3’s deep sleep mode, but with the microphone and turn the device on with some voice recognition. That’d be so cool! (for now it’ll turn on with a button press.) I just finished the board design I think…
I really hope this works, it’s the most intense design I’ve ever done 
