OK, but what if we connected the RTC to the EN pin instead of the D8? That way, the Alarm would turn on the power for the device itself. For now, we can table this but it could be something to look at in the future.
So, proposal is to go with @rickkas7 RTC and library integrated into this board.
Chip
Chip
I use a slightly different circuit with the MCP79410 to control the EN line on the Boron. It also requires a NL17SZ74 flip-flip, some N-channel MOSFETs (2N7002) and pull resistors.
Using this circuit the idle current drops to around 75 uA which gets pretty good battery life. This is only recommended for long sleep durations; I wake once a day.
It does not use an external coin cell or supercap. The VBAT pin on the RTC and VCC on the flip-flop connect directly to the Li+ pin (no regulator required).
I think this is a nice application of this RTC and would work well for longterm or short term sleep with perhaps a jumper (A-com-B type), that allows the wakeup to either go via driver circuitry to EN or to a wakeup pin (perhaps also an IO to detect the watchdog āmodeā)
Thank you for sharing this circuit. I am planning to use the MCP79410 on the carrier board in large part because of the great library you have provided.
I want to make sure I understand your circuit and I apologize if these are basic questions. Please let me know if I have this right.
Thank you
Chip
I agree that they buried the lead here but, on page 21 of the datasheet, it does say that the alarm interrupt function is available on battery power.
So, looks like we have a winner.
Chip
Yes, you are correct. There is no electrical reason you canāt use it to go to sleep for shorter periods. however the EN line powers down the modem and you will use significantly more power reconnecting to cellular than you would use SLEEP_NETWORK_STANDBY for sleep periods less than 15 minutes or so.
Since the 3V3 line is not powered when EN is low, the RTC and associated circuitry must be powered from Li+. Since that can be as high as 4.2V, the MOSFETs prevents high voltages from damaging the GPIO or applying a voltage higher than 3.3V on the EN line which has a pull-up to 3V3.
To power cycle your device, you could set an alarm for 10 seconds into the future and then bring D3 high. This would pull the EN line low and then the alarm interrupt would bring EN back high when the alarm goes off. Right?
Thanks,
Chip
All, I have redesigned the board to incorporate @rickkas7 's Real Time Clock circuitry and all the other great suggestions from this group. My plan is to get a small batch of these made at MacroFab (if I am brave / confident) or have one more run of boards from OSHPark if I am not.
Changes - New Features:
Please look at the schematics and let me know if I have made any major mistakes.
I am not sure how to offer the RTC functionality if there is no LiPO battery. To be honest, I am not sure how important the RTC is if you are operating the Boron without a battery. Comments welcome here.
Once I am sure about the schematics, I will redo the layout.
Thanks,
Chip
OK, here is the next revision. I am looking for any advice on things I missed as I plan to get a few of these made for final testing.
Here are the big changes:
I might still beautify the layout but please let me know if I am doing something wrong here. I want to wrap this up so I can move on to the new M2 carrier.
Thanks,
Chip
I havenāt studied your schematics yet, but It looks like you might have The LiPo connector, C5, U4, and R9 within the keepout area for the Boron. I donāt know how hard a requirement that keepout area is, but you may want to consider it.
Thank you for taking a look. C5, U4 and R9 are on the underside of the board (red pads) while the Boron is on the top. The LiPO connector is the only potential issue but, I have tested this clearance on a previous iteration of the board (see pictures above in this thread) and we are good.
Please keep those questions and comments coming.
Also, wondering if I should take the FRAM off the board as it is a $2 chip and the Boron will eventually have its flash memory available for use.
Thanks,
Chip
Iām leaving the FRAM on my board for now since I have the code working well, even though I pay about $3 per chip (256Kb). I bought a reel of 100 of them though, so itās a sunk cost for my prototypes. In the future, once the 2MB flash is exposed to us, I can simply depopulate the chip, or remove it completely from the design. I do like the fact that it doesnāt have destructive writes, so I am considering possible uses for that even once onboard flash is available for certificate and configuration storage.
@chipmc,
For the non-guruās (like me), whatās changed or been added from the wish list in your original post, for your current design ?
Thanks in advance
Great question, especially since this thread dates back to March!
Here is what I had originally outlined:
I would say that all of these are met with one (small?) exception. The ability to power cycle the device is limited to use cases where the device has a LiPO battery installed. I am wondering if this is a big deal and, if so how best to accomplish this. I have toyed with some solutions but all came with cost and complexity that I felt was not worth the benefit. Comments welcome.
In addition to the original list, there are two big additions:
Take a look and let me know what I could do to improve.
Thanks, Chip
This all looks great, Chip. I donāt see any obvious errors in it. The one suggestion I have, and itās really just based on personal preference, is to replace the TMP36 temperature sensor with a DS18B20Z+. Itās easy to interface to and much more accurate than AD conversion on the Boron.
@chipmc, Thanks for the Update!
I have a few questions. I appoligize in advance if they are stupid or silly.
Power:
Since youāve added the MCP79410, what purpose does the TPL5010 serve?
Looking at @rickkas7ās Library, it appears to have a ton of useful features.
Temperature:
Iāve used TMP36/37ās to help decide when to disable Li-Po charging, but that only works when the Boron is awake obviously. In reality, there are only 4-6 hours a day that the enclosure temperatures can get too high, and thatās mainly a few months in each year.
It appears to me that with the MCP79410, a progressive or regressive Sleep/Shutdown schedule will be easier to implement. IE: Wake up a few times during the Hottest times of Summer Days even if you donāt need data, just to check the Temperature and disable charging if Reqād.
Would that be possible with the TPL5010 onboard ?
External Interrupt:
If the Boron is Shutdown via EN pin by the MCP79410 and a Motion Sensor is activated, how can that Interrupt be handled by the MCP ? I assume thatās only possible with the TPL and not using the MCP and EN pin?
Again, Iām sorry if these are stupid questions. Iām very interested in your Carrier Board even if itās āOver My Headā.
Great questions and the whole purpose of posting all this here is to make sure I have thought all this through. Thanks for asking them.
Power: My devices are in remote spots and the watchdog timer is there to make sure - not matter what I screw up in the software, the device will be reset if unresponsive. The clock could do the same thing but, what if the i2c bus locks up or something happens that prevents the RTC alarm from being set? At least that is my rationale.
Temperature: With a watchdog set to 1 hour, the device will wake on that schedule. I figure that checking the temp is quick and easy but, to your point, every hour and every month is likely overkill. Note, if the RTC turns off the device with the EN pin, it switches off the watchdog as well.
External Interrupt: You are correct, shutting down the device with the EN pin prevents the device from servicing interrupts. I am thinking this is OK for two reasons: 1) The EN sleep will be for longer periods - overnight for example and 2) I have an idea for a super low power data collection device.
Make Sense?
Chip
@chipmc, Thanks for the detailed response.
That was an important (and beneficial) aspect that I overlooked.
So, normal operation is to wake every hour and decide if starting the Modem and a Publish is necessary, then quickly trigger the TPL's done pin.
We can also use the RTC as a fail-safe to allow much longer sleep times (actually Shutdown via EN pin) in the event that Battery Voltage has dropped too low. The only goal during the fail-safe Shutdown is to allow the Battery Voltage to recover, before resuming normal operations.
Another thought about the TPL5010 + MCP7941X (RTC) as an Alternate Use-Case:
I don't have experience with the TPL5010, but I know the TPL5011 will reset the device if the DONE pin isn't triggered within the time period set by the resistors. The Sleep Time also becomes the maximum AWAKE Time (unless you tickle the delay pin on purpose). It seems your board might allow us to alternatively use the RTC as the adjustable Sleep (Shutdown) Timer for everyday use. The TPL5010 would only reset the Boron after 1 hour of AWAKE time if something went terribly wrong and the Boron didn't set the next RTC alarm over I2C ? The RTC would handle the normal Shutdown intervals and is infinitely adjustable on the fly.
IE: The MCP7941X (RTC) handles the WAKE Time, the Boron decides the next Sleep interval (or specific time/date) and resets the RTC for the next Wake time. The TPL watchdog becomes secondary to ensure a complete Power Cycle Restart if the Boron stays Awake longer than 1 hour (our Code crashed).
5.4 Alarms
The MCP7941X features two independent alarms. Each alarm can be used to either
generate an interrupt at a specific time in the future, or to generate a periodic interrupt
every minute, hour, day, day of week, or month.
Please let me know if my above assumptions are incorrect.
Thanks Again Chip !
Just a question - you have the BATT-IN line being switched through the TPS22810 to LI+.
If this switch is unidirectional - how does the lipo charge?
secondly - this may have been covered already - if using an Argon/Xenon, the (potential) 6VDC from the panel (on VUSB after F1, is above the regulator limits - you will need a Zener diode to clamp the voltage - the TVS diode is great for surges but not to clamp a voltage to a set point over time.
Thank you for the suggestion. The DS18B20Z+ is a cool part (parasitic power!) and is more accurate than the TMP-36. I would be interested in getting more folks opinion but, here is the rationale for keeping the TMP-36:
More thoughts on this?
Chip