Author Topic: coin cell powered R4  (Read 12948 times)

davegravy

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coin cell powered R4
« on: April 21, 2016, 09:48:56 PM »
After trying to power my project from two 3v coin cells in series (need 3.5V min for my sensor), and getting only 2 transmissions out of it (1min apart) before it became unresponsive due to voltage drop, I found and read this thread:

https://lowpowerlab.com/forum/index.php?topic=1340.0

I'm a newb and am probably trying to do stuff that is more advanced than I'm currently able to... So I have some followup questions!

1) Is the R4 a practical platform to achieve a low duty cycle coin-cell powered sensor? The other PCB designs in that thread are more optimized for compactness, but I feel like there are hardware-based power optimizations going on. If so can someone try to explain them?

2) My sleeping current in listenmode is 20uA with BOD and ADC off. There are big spikes in current consumption once per second that account for much of this. Is this normal?

3) I read the recommendation to use BOD in place of a cap/supercap. I assume this doesn't mean to avoid BOD_OFF in LowPower.powerDown(SLEEP_FOREVER, ADC_OFF, BOD_OFF), but means BOD should be ON while awake. Do I need to explicitly turn BOD on after listenModeEnd() or does it come on by default?

4) The thread mentions setting BOD "bits" to 1.8V.  Can the moteino actually survive voltage drops as low as 1.8V without impacting execution?  If not, what's the benefit to this over the default BOD setting (2.7V?)

5) What battery voltage is considered "acceptable" to send a transmission without killing the supply voltage?

6) It's mentioned that no ACKs are used in communication, but I understand sendWithRetry is necessary to use ATC, correct? Is lower transmit power worth giving up for the shorter transmit time that no ACKs gives?

7) I haven't observed an issue with startup voltage dips yet, but the thread mentions running at 1MHz instead of 8Mhz during startup to keep consumption low, and I think says it upclocks to 8Mhz afterwards. Is this something that can be controlled via software dynamically? I see there are "fuse settings" for clock rate but they seem like static settings... Are there code examples of how to do this?

Thanks in advance!

Dave
« Last Edit: April 22, 2016, 12:05:16 AM by davegravy »

TomWS

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Re: coin cell powered R4
« Reply #1 on: April 22, 2016, 08:12:54 AM »
You fell off the front page too soon...

After trying to power my project from two 3v coin cells in series (need 3.5V min for my sensor), and getting only 2 transmissions out of it (1min apart) before it became unresponsive due to voltage drop, I found and read this thread:

https://lowpowerlab.com/forum/index.php?topic=1340.0

I'm a newb and am probably trying to do stuff that is more advanced than I'm currently able to... So I have some followup questions!
EDIT: IMO 1min transmission cycles are too fast to get any useful life out of a coin cell.  The duty cycle is too high.  If I have periodic reporting with a coin cell, I'll use 10 minute intervals as a minimum.
Quote

1) Is the R4 a practical platform to achieve a low duty cycle coin-cell powered sensor? The other PCB designs in that thread are more optimized for compactness, but I feel like there are hardware-based power optimizations going on. If so can someone try to explain them?
The R4 design is usable with coin cell IFF you remove the MCP1703 voltage regulator, reprogram the fuses to work with internal 8MHz RC clock, and remove or replace the flash memory with a lower power flash chip.  Also, only Joe Lucid seems to be able to reliably run an RFM69HW on a coin cell.  The rest of us mortals use RFM69W devices.
Quote

2) My sleeping current in listenmode is 20uA with BOD and ADC off. There are big spikes in current consumption once per second that account for much of this. Is this normal?
IMO this is too high to operate on a coin cell.   You need to have your sleeping current in single digit or less (and operating between 2.8-3.0V).
Quote

3) I read the recommendation to use BOD in place of a cap/supercap. I assume this doesn't mean to avoid BOD_OFF in LowPower.powerDown(SLEEP_FOREVER, ADC_OFF, BOD_OFF), but means BOD should be ON while awake. Do I need to explicitly turn BOD on after listenModeEnd() or does it come on by default?

4) The thread mentions setting BOD "bits" to 1.8V.  Can the moteino actually survive voltage drops as low as 1.8V without impacting execution?  If not, what's the benefit to this over the default BOD setting (2.7V?)
I believe the BOD discussion is outdated.  Other techniques are now used to manage coin cell operations.  Further, BOD off requires a mod to the LowPower library if you're using Arduino IDE 1.6 or later (search this forum) for how.
Quote

5) What battery voltage is considered "acceptable" to send a transmission without killing the supply voltage?
If using a RFM69W, I wouldn't TX if the voltage from a single cell is less than 2.7V.  I wouldn't use two coin cells in series, its wasted energy - use a bigger coin cell.
Quote

6) It's mentioned that no ACKs are used in communication, but I understand sendWithRetry is necessary to use ATC, correct? Is lower transmit power worth giving up for the shorter transmit time that no ACKs gives?
You can use sendWithRetry with 0 retry count.  This will wait for a single Ack and give up if none received.  This does consume a bit more power but if you're particular on WHICH packets get sent sendWithRetry() you'll get ATC control but not waste power on multiple TXs.
Quote

7) I haven't observed an issue with startup voltage dips yet, but the thread mentions running at 1MHz instead of 8Mhz during startup to keep consumption low, and I think says it upclocks to 8Mhz afterwards. Is this something that can be controlled via software dynamically? I see there are "fuse settings" for clock rate but they seem like static settings... Are there code examples of how to do this?
I'll take a look at what I have, but I'd suggest reading up on the various fuse settings and check out the AVR fuse calculator: http://www.engbedded.com/fusecalc/ to learn what choices are available...

EDIT: You will also need to update the Moteino BOARDS.TXT file to include a new section for an 8MHz version (CPU Freq=8MHz, upload speed=57600, and new fuse settings).

Tom
« Last Edit: April 22, 2016, 08:32:46 AM by TomWS »

TomWS

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Re: coin cell powered R4
« Reply #2 on: April 22, 2016, 08:34:48 AM »
After trying to power my project from two 3v coin cells in series (need 3.5V min for my sensor)
What sensor are you using and how is it wired (switched power or not)?

Tom

davegravy

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Re: coin cell powered R4
« Reply #3 on: April 22, 2016, 10:03:11 AM »
Thanks kindly for the insight, Tom!

Quote
EDIT: IMO 1min transmission cycles are too fast to get any useful life out of a coin cell.  The duty cycle is too high.  If I have periodic reporting with a coin cell, I'll use 10 minute intervals as a minimum.

Just to clarify I intend to provide regular updates on a 1hr interval. The 1min was in testing.  I'd like to have the user able to request an unscheduled update, have the node detect if there's insufficient battery voltage to service the request, and act accordingly. Maybe I misunderstood but that seems to be what you accomplished (or maybe it was Joe).

Quote
The R4 design is usable with coin cell IFF you remove the MCP1703 voltage regulator, reprogram the fuses to work with internal 8MHz RC clock, and remove or replace the flash memory with a lower power flash chip.  Also, only Joe Lucid seems to be able to reliably run an RFM69HW on a coin cell.  The rest of us mortals use RFM69W devices.

Is it insufficient to power the M4 directly via the 3.3V pin? Doesn't this effectively bypass the regulator? I'm currently sleeping the flash -  I understood there's not a lot to be gained by completely removing it, but it sounds like that may not be true.
 
Quote
I believe the BOD discussion is outdated.  Other techniques are now used to manage coin cell operations.  Further, BOD off requires a mod to the LowPower library if you're using Arduino IDE 1.6 or later (search this forum) for how.

Sorry, I'd understood that options were a) use large bulk caps or b) use BOD (1.8V) and monitor VCC health - using it as a condition for making transmissions. If there's a newer/better approach, i'm eager to learn about it. Are there some keywords or something you can give me to search with? Google's not being friendly to me on this one.

Quote
What sensor are you using and how is it wired (switched power or not)?
Vegetronix VH400 moisture sensor. +ive supply is wired direct to 6V battery rail, gnd supply goes to a digital pin 5 which switches power (same digital pin completes the circuit for a 1MOhm-1MOhm voltage divider used to monitor battery voltage). Sensor requires 400ms power before output stabilizes so I've been doing
Code: [Select]
LowPower.powerDown(SLEEP_XX, ADC_OFF, BOD_OFF)
for that time. It draws around 7mA.

I should note that with my existing power profile and 1hr updates, I calculated an average current of 23uA - that should mean my 190mAH battery lasts 8 months I think. To me that's close to acceptable and I mainly need to sort out resilience against the high battery ESR.

Thanks again Tom.

Dave

snorp

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Re: coin cell powered R4
« Reply #4 on: April 22, 2016, 10:32:17 AM »
<snip>
Further, BOD off requires a mod to the LowPower library if you're using Arduino IDE 1.6 or later (search this forum) for how.

This is fixed in github, so you if you use that no modification is necessary. Don't use the "library manager" thing in the IDE.

davegravy

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Re: coin cell powered R4
« Reply #5 on: April 22, 2016, 01:44:35 PM »
I suppose I could bypass the regulator and power the moteino from the first 3V lithium and supply the VH400 from 6V stacked on top

Like this: http://goo.gl/udrF6v

The lower 3V battery will presumably drain faster than the upper, so it's not ideal, but the best I can think of without a 3V only supply and step-up converter (which I assume would have a significant power cost associated with it).

davegravy

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Re: coin cell powered R4
« Reply #6 on: April 23, 2016, 12:42:01 AM »
In my reading it looks like a lot of people are getting false current readings due to measurement technique.

Using a mains-powered voltage supply, I'm measuring current draw of my moteino by putting a 10 ohm shunt resistor between the +IVE supply and the Vcc node, and measuring voltage across it with a scope (differential, and which accurately measures voltages below the uV range).

Is this a valid approach?

joelucid

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Re: coin cell powered R4
« Reply #7 on: April 23, 2016, 06:04:56 AM »
If you apply 6v to a tri-State gpio pin you'll get a nice current through the esd diodes of the 328p. You need to switch gnd with an n-fet instead. Often even that isn't enough since the sensor output will get pulled up to 6v when gnd is disconnected. Then you need a second p-fet to switch +6v instead.

Other than that I think this should work with 2 coin cells. The rfm69hw also should not be a problem. But you should not run it at max power. And I'd recommend modifying the rfm69 lib to always return true in canSend. Sitting 1s in rx could kill your coin cell.


emjay

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Re: coin cell powered R4
« Reply #8 on: April 23, 2016, 06:17:25 AM »
@davegravy,

Yes, a valid method. Here is exactly the same technique in use http://jeelabs.org/2013/05/10/maxing-out-the-hameg-scope/index.html  It is handy if the 'scope has some averaging capability since at the uA level, the signal has a little noise superimposed.


davegravy

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Re: coin cell powered R4
« Reply #9 on: April 23, 2016, 12:19:44 PM »

Is it insufficient to power the M4 directly via the 3.3V pin? Doesn't this effectively bypass the regulator?
 

Answering my own question.. according to https://lowpowerlab.com/forum/index.php/topic,671.msg4238.html#msg4238

Quote
Note that the LDO must be completely removed, just bridging its Vin to Vout or leaving Vin open circuit with power on Vout will still have a quiescent drain.
« Last Edit: April 23, 2016, 02:03:46 PM by davegravy »

davegravy

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Re: coin cell powered R4
« Reply #10 on: April 24, 2016, 10:08:48 AM »
If you apply 6v to a tri-State gpio pin you'll get a nice current through the esd diodes of the 328p. You need to switch gnd with an n-fet instead. Often even that isn't enough since the sensor output will get pulled up to 6v when gnd is disconnected. Then you need a second p-fet to switch +6v instead.

Seems like you're right - I am losing a few uA through my power switching configuration, and VH400 output does go high. A little confused if you are saying I need to switch GND and +6V or just +6v. I think if I just used a high-side switch... like:

http://electronics.stackexchange.com/a/67349

... and be ok. Problem is I've never seen pullup/down resistors in the MOhms range, which is what I'd need to keep current draw < 1uA.  I need to brush up on MOSFET theory to figure out what implication that'd have.

EDIT: Found this http://www.eetimes.com/document.asp?doc_id=1272463 While these are normally ON designs, at least it seems like high resistor values aren't generally a problem.

EDIT2: Also, usefull info on selecting MOSFETs with low leakage http://electronics.stackexchange.com/questions/98597/low-drain-source-mosfet-leakage
« Last Edit: April 24, 2016, 12:28:16 PM by davegravy »

WhiteHare

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Re: coin cell powered R4
« Reply #11 on: April 24, 2016, 12:43:34 PM »
Just curious:  Is there any advantage to making your load switch from separate parts instead of just buying a single integrated load switch chip?  One of the recent threads (elsewhere on this forum) did talk about the ability to tweak rise and fall times for less abrupt switching by resistor selection on a semi-integrated chip (n and p channels on one chip that you then have to finish wiring yourself) or equivalently using entirely separate parts as you are suggesting, but if your goal is just a fast on-off switch with minimal quiescent current, then the SI1869DH (https://lowpowerlab.com/forum/index.php?topic=1579.0) just seems smaller and easier and, if need be, can even switch as much as 20v. 

[Edit: i.e. it seems like a good "go to" chip to keep on hand for use in all sorts of projects. ]

« Last Edit: April 24, 2016, 01:16:29 PM by WhiteHare »

joelucid

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Re: coin cell powered R4
« Reply #12 on: April 24, 2016, 12:50:04 PM »
Yeah I meant exactly the high side p-fet controlled by logic n-fet setup. 5 meg pull-ups are no problem.

davegravy

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Re: coin cell powered R4
« Reply #13 on: April 25, 2016, 03:13:51 PM »
... but if your goal is just a fast on-off switch with minimal quiescent current, then the SI1869DH (https://lowpowerlab.com/forum/index.php?topic=1579.0) just seems smaller and easier and, if need be, can even switch as much as 20v. 

That simplifies things quite a bit.

My new approach is to ditch the 2nd battery, use a larger single cell, and use a boost converter to get >3.5V needed for the VH400. If I understand correctly, that lets me remove the Moteino regulator, and instead of needing a voltage divider circuit into an analog input pin, I can then just read VCC directly.

The TPS61222DCKR is 90% efficient at my operating condition, which translates to 770uA waste for the 400ms that the sensor is powered up. If I'm sampling once per hour, that's an average current increase of 85nA... i.e not much.



joelucid

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Re: coin cell powered R4
« Reply #14 on: April 25, 2016, 04:03:38 PM »
Well in that case you can just switch the booster itself via the en pin. No load switch necessary. One thing to keep an eye on is input current. Coin cells are not good at providing larger currents for long periods of time. You'll need more than the specified current of the humidity sensor because you're converting the voltage up. Probably still ok - in particular with a cr2450 - but it's a pretty big load for a coin cell.

TomWS

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Re: coin cell powered R4
« Reply #15 on: April 25, 2016, 05:43:59 PM »
Well in that case you can just switch the booster itself via the en pin. No load switch necessary. One thing to keep an eye on is input current. Coin cells are not good at providing larger currents for long periods of time. You'll need more than the specified current of the humidity sensor because you're converting the voltage up. Probably still ok - in particular with a cr2450 - but it's a pretty big load for a coin cell.
I'd be concerned about the quiescent current using the EN pin.  A single P FET would have much lower leakage.  No need for the N FET.

Also, what type of soil and depth are you planning to use the VH400.  In my experience this device was totally useless in North Carolina clay.  It seems to work reasonably well in potting soil, however.

Tom

perky

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Re: coin cell powered R4
« Reply #16 on: April 25, 2016, 05:45:49 PM »
Bear in mind there's probably also a DC path through the booster from Vin to Vout via the inductor and diode, this means you'll have at least Vin minus a diode drop on Vout regardless of whether you use an enable pin. You may need a high side switch on the input to the booster if you want to isolate completely.
Mark.
Edit: You might want to slew rate control that high side switch (just a P channel FET, no need for the botton N channel FET). One way to do that is put a resistor in series with the enable voltage and the gate, and have a capacitor from the switched output to the gate. Here's a useful app note: www.onsemi.com/pub/Collateral/AND9093-D.PDF
« Last Edit: April 25, 2016, 06:24:01 PM by perky »

davegravy

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Re: coin cell powered R4
« Reply #17 on: April 25, 2016, 08:39:45 PM »
Also, what type of soil and depth are you planning to use the VH400.  In my experience this device was totally useless in North Carolina clay.  It seems to work reasonably well in potting soil, however.
Tom

Was planning for about 4" down, and the soil around here is pretty sandy. Testing in my local soil so far it's performed reasonably well.

But I was hoping the sensor would work well in other soils too so I could build these for some interested friends. How did it behave badly in clay soil? Did a tiny drop of rain send it straight to full scale output? Did you find another sensor that worked better in clay?


TomWS

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Re: coin cell powered R4
« Reply #18 on: April 25, 2016, 09:28:54 PM »
Also, what type of soil and depth are you planning to use the VH400.  In my experience this device was totally useless in North Carolina clay.  It seems to work reasonably well in potting soil, however.
Tom

Was planning for about 4" down, and the soil around here is pretty sandy. Testing in my local soil so far it's performed reasonably well.

But I was hoping the sensor would work well in other soils too so I could build these for some interested friends. How did it behave badly in clay soil? Did a tiny drop of rain send it straight to full scale output? Did you find another sensor that worked better in clay?
I started a test in October where I planted it in the vicinity of a Watermark sensor that has been working well for about a year; just to compare results. 

The area was a landscaped section (shrubs & perenials) next to a strip of lawn and the Watermark is buried about 8".  The VH400 could only go from the surface to about 5-6" deep.  It was a wet fall and winter so both devices were reading 'wet' for most of the time (the VH400 ALL of the time). 

Finally, this Spring, the Watermark started to show signs of water uptake by the surrounding plants and eventually read "It's time to water." but the VH400 barely waivered from reading 'wet'. 

I finally gave up on it and moved it to a pot where we've planted some Basil in potting soil just to see if it worked at all and it seems to be behaving in an expected, albeit uncalibrated, way.  Sandy, loamy soil where the roots are shallow (ie no more than 6" deep) is probably ok.  I wouldn't use this in denser soil or for shrubs/deeply rooted plants, and, frankly, won't buy another one.

Tom

TomWS

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Re: coin cell powered R4
« Reply #19 on: April 25, 2016, 09:33:12 PM »
Bear in mind there's probably also a DC path through the booster from Vin to Vout via the inductor and diode, this means you'll have at least Vin minus a diode drop on Vout regardless of whether you use an enable pin.
LOL!  Oh yeah, that would be a bit more 'leakage' than I had suggested!  Good call!
Quote
Edit: You might want to slew rate control that high side switch (just a P channel FET, no need for the botton N channel FET). One way to do that is put a resistor in series with the enable voltage and the gate, and have a capacitor from the switched output to the gate. Here's a useful app note: www.onsemi.com/pub/Collateral/AND9093-D.PDF
Excellent suggestion!  The 10uF cap will represent a very hefty 'short' to the high ESR battery and may actually reset your processor without some slew rate control.

Tom

davegravy

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Re: coin cell powered R4
« Reply #20 on: April 25, 2016, 11:08:59 PM »

I started a test in October where I planted it in the vicinity of a Watermark sensor that has been working well for about a year; just to compare results. 

The area was a landscaped section (shrubs & perenials) next to a strip of lawn and the Watermark is buried about 8".  The VH400 could only go from the surface to about 5-6" deep.  It was a wet fall and winter so both devices were reading 'wet' for most of the time (the VH400 ALL of the time). 

Finally, this Spring, the Watermark started to show signs of water uptake by the surrounding plants and eventually read "It's time to water." but the VH400 barely waivered from reading 'wet'. 

I finally gave up on it and moved it to a pot where we've planted some Basil in potting soil just to see if it worked at all and it seems to be behaving in an expected, albeit uncalibrated, way.  Sandy, loamy soil where the roots are shallow (ie no more than 6" deep) is probably ok.  I wouldn't use this in denser soil or for shrubs/deeply rooted plants, and, frankly, won't buy another one.

Tom

The first VH400 I had somehow lost the bottom half of it's dynamic range, so wouldn't read below 1.5V even when dry and sitting in air. Vegetronix is shipping me a replacement at no cost. I wonder if something similar might have happened to yours?

But you've been happy with the Watermark? Hadn't heard of it - might have to pick one of those up to test. This is for lawn watering alerts, so shallow roots. 

joelucid

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Re: coin cell powered R4
« Reply #21 on: April 26, 2016, 12:35:25 AM »
Quote
Bear in mind there's probably also a DC path through the booster from Vin to Vout via the inductor and diode, this means you'll have at least Vin minus a diode drop on Vout regardless of whether you use an enable pin. You may need a high side switch on the input to the booster if you want to isolate completely.

 :D - good catch, I missed that, thanks.

perky

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Re: coin cell powered R4
« Reply #22 on: April 26, 2016, 04:19:33 AM »
Thinking about this further, high current pulses from coin cells can significantly reduce their capacity so I would probably do the following:

1) Use a high side switch with aggressive slew rate control
2) Use the smallest input and output bulk capacitors that the boost regulator needs (10uF is probably too high)
3) Use a boost regulator with a very slow soft start, preferably one I that can be programmed with an external component like a capacitor, and
4) Enable the boost regulator some time later once the input has reached working voltage of the regulator

Mark.
 

SadE54

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Re: coin cell powered R4
« Reply #23 on: April 26, 2016, 05:40:34 AM »
Maybe it could be a solution in this case :
https://lowpowerlab.com/forum/index.php/topic,1831.0.html

davegravy

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Re: coin cell powered R4
« Reply #24 on: April 26, 2016, 08:15:02 AM »
Thinking about this further, high current pulses from coin cells can significantly reduce their capacity so I would probably do the following:

1) Use a high side switch with aggressive slew rate control
2) Use the smallest input and output bulk capacitors that the boost regulator needs (10uF is probably too high)
3) Use a boost regulator with a very slow soft start, preferably one I that can be programmed with an external component like a capacitor, and
4) Enable the boost regulator some time later once the input has reached working voltage of the regulator

Mark.

Thanks for the discussion guys, this is all stuff I'd have to learn the hard way otherwise...

In terms of an optimal rise time for the boost regulator supply to prevent processor restarts, I expect this is something that'll have to be determined experimentally, but if there's any reasonably simple analytical method you're aware of then please do share.

As I understand, another means (perhaps good to be used in tandem with the above methods) to mitigate voltage drops from load switching is bulk caps right after the battery.
« Last Edit: April 26, 2016, 08:16:48 AM by davegravy »

davegravy

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Re: coin cell powered R4
« Reply #25 on: May 01, 2016, 10:10:03 PM »
I started to prototype the boost converter on breadboard and when it didn't work I remembered that high freq circuits and breadboards don't get along. Going straight to PCB without bread-boarding first makes me really nervous.

Is there something like the TPS61222 but all in one package (i.e not requiring discrete capacitors/inductor) I can use on a breadboard. TI has an evaluation board for this boost converter but it' >$50 which breaks my hobby budget.

Otherwise I guess I'll have to go straight to PCB and tweak component values by soldering/desoldering.

TomWS

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Re: coin cell powered R4
« Reply #26 on: May 01, 2016, 11:48:13 PM »
I started to prototype the boost converter on breadboard and when it didn't work I remembered that high freq circuits and breadboards don't get along. Going straight to PCB without bread-boarding first makes me really nervous.

Is there something like the TPS61222 but all in one package (i.e not requiring discrete capacitors/inductor) I can use on a breadboard. TI has an evaluation board for this boost converter but it' >$50 which breaks my hobby budget.

Otherwise I guess I'll have to go straight to PCB and tweak component values by soldering/desoldering.
I think you should do the two battery approach or go with a battery that's high enough voltage to operate the VH400 (LiPo probably will).  Or dump that VH400 and use a different moisture sensor (Chirp I2C for instance) which will work within your voltage budget.  The boost circuit is an 'optimizer' solution (and, as you've observed, requires fab skills that may be challenging) and you should probably get your 'feet wet' with a 'good enough' solution.

If you REAAAALLLLY want to try the boost circuit, LowPower Labs and others sell a SOT-23 breakout board that will work with the TPS61222 (SC-70 package I believe) but that could be unstable due to poor layout compromises.

Tom

joelucid

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Re: coin cell powered R4
« Reply #27 on: May 02, 2016, 02:48:11 AM »
Quote
The boost circuit is an 'optimizer' solution (and, as you've observed, requires fab skills that may be challenging) and you should probably get your 'feet wet' with a 'good enough' solution.

Also boosters are inherently noisy and might well increase your noise floor, with a negative impact to radio sensitivity. I never fully realized how important that is until my recent noise tests.

perky

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Re: coin cell powered R4
« Reply #28 on: May 02, 2016, 04:48:29 AM »
They can be, but you need to follow careful guidelines when laying them out e.g. reducing the two current loops, minimizing stray inductance, using snubbers to remove ringing, proper post filtering and pre-filtering, careful placement, using shielded inductors. You can filter practically all conducted noise with adequate power supply filtering and what's left is E and H fields which can be minimized. Trying to put a switching regulator on a piece of veroboard is not a good idea for noise, you really need proper PCB layout.
Mark.

damonb

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Re: coin cell powered R4
« Reply #29 on: May 02, 2016, 04:59:50 AM »
@davegravy, I don't know how attached you are to your design goals, but for comparison I power my soil nodes from 3 x AA alkaline cells. The VH400s are switched from a JeeNode's regulated 3.3V rail via a P-MOSFET high-side switch. I get about 2 years battery life sampling soil and temperature (DS18B20) every 10 minutes. I chose to use the 3.3V regulated instead of the battery rail as the VH400 output is somewhat proportional to the supply voltage, and hence the calibration varied as the alkalines ran down. This way i can run them down to just under 1.2V per cell.
It would save a lot of R&D time messing with boost regulators.

joelucid

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Re: coin cell powered R4
« Reply #30 on: May 02, 2016, 05:12:06 AM »
Quote
They can be, but you need to follow careful guidelines when laying them out e.g. reducing the two current loops, minimizing stray inductance

No kidding - mine only tend to work well if I let Tom put the finishing touches on my design  :)

perky

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Re: coin cell powered R4
« Reply #31 on: May 02, 2016, 05:16:56 AM »
BTW Linear do some nice ultra-low EMI boost regulators. Their app notes include designs for post and pre filtering on the power supply to reduce conducted noise and have PCB layout recommendations. If you're unsure what you're doing then follow the design layout guidlines to the letter, do exactly as they say and you should get a quiet design.
Mark.
« Last Edit: May 02, 2016, 06:39:13 AM by perky »

joelucid

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Re: coin cell powered R4
« Reply #32 on: May 02, 2016, 05:30:49 AM »
Thanks. I recently read up a little on the subject of noise filtering (e.g. http://www.murata.com/~/media/webrenewal/support/library/catalog/products/emc/emifil/c39e.ashx is pretty thorough). So I hope I know a little more now.

I'm getting the first rev of my noise filtered espgw board today. It uses a mic5219 ultra low noise regulator, common mode choke, 3 terminal filter cap, ferrite bead and several decoupling caps to filter the power supply and a MAX14850 as digital isolator on the SPI / DIO0 lines. Can't wait to see how it'll do on a noisy power supply.

davegravy

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Re: coin cell powered R4
« Reply #33 on: May 02, 2016, 05:09:24 PM »
I'm going to push forward a bit further with the boost converter...  Pulled the assembly off my solderless breadboard and direct soldered my components to the DIP adapter to keep leads as short as possible.  See attached picture.

Works now... at least, it gives me expected output voltage. Not sure about EMI, ripple current, efficiency or anything else yet.  But if I can get the whole project working with it, then things should only get better when it gets PCB-ized, right?.


TomWS

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Re: coin cell powered R4
« Reply #34 on: May 02, 2016, 05:25:43 PM »
I'm going to push forward a bit further with the boost converter...  Pulled the assembly off my solderless breadboard and direct soldered my components to the DIP adapter to keep leads as short as possible.  See attached picture.

Works now... at least, it gives me expected output voltage. Not sure about EMI, ripple current, efficiency or anything else yet.  But if I can get the whole project working with it, then things should only get better when it gets PCB-ized, right?.
Gee, I don't know... I think your implementation has that sort of je ne sais quoi that is so appealing!   8)

Rule #1 for hobbyist implementation: If it works, what the hey?  Go for it.  Let us know how the entire scheme works!

Tom

davegravy

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Re: coin cell powered R4
« Reply #35 on: May 04, 2016, 10:38:34 PM »
Drawing 9uA 6.2uA now in listenmode.

Steps I've taken:

* Pulled the regulator
* switched to internal oscillator @ 8Mhz
* reduced BOD fuse to 1.8V

Code: [Select]

for (uint8_t i=0; i<=A5; i++)
{
   pinMode(i, OUTPUT);
   digitalWrite(i, LOW);
}

flash.initialize()
flash.sleep()
radio.listenModeStart();
LowPower.powerDown(SLEEP_FOREVER, ADC_OFF, BOD_OFF);

I recall reading that ~2uA is possible in listenmode. I'd rather keep the flash soldered, so I realize I might not get all the way there, but I should be able to do better right?. I haven't experimented with dropping the clock rate further, but what else can I do?

I tried
Code: [Select]
 disable_wdt(); 
but it had no effect. Guessing that gets called already within the powerDown function.
« Last Edit: May 05, 2016, 10:26:34 AM by davegravy »

davegravy

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Re: coin cell powered R4
« Reply #36 on: May 05, 2016, 10:25:25 AM »
Scope calibration was off, actual consumption is 6.2uA, not 9.0

For comparison's sake I loaded the deepsleep example sketch and I'm getting 4.8uA.

At this point I think idle power draw is acceptable to meet my stated goals, and I've just developed an irrational obsession with cutting power. You guys gave me some kind of bug  :o
« Last Edit: May 05, 2016, 10:29:29 AM by davegravy »

joelucid

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Re: coin cell powered R4
« Reply #37 on: May 05, 2016, 10:48:57 AM »
Quote
You guys gave me some kind of bug  :o

The lowest power mode with stock moteinos is to use the radio as timer by using listen mode with a RSSI thresh of 255. That gets you down to around 1.2uA. I ended up with a combination of listen mode and this low power setup. Essentially I switch to listen mode when I need interactivity and otherwise use the timer.

Felix

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Re: coin cell powered R4
« Reply #38 on: May 05, 2016, 11:20:03 AM »
The lowest power mode with stock moteinos is to use the radio as timer by using listen mode with a RSSI thresh of 255. That gets you down to around 1.2uA. I ended up with a combination of listen mode and this low power setup. Essentially I switch to listen mode when I need interactivity and otherwise use the timer.

What timer do you refer to? Some kind of interrupt in listen mode?

WhiteHare

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Re: coin cell powered R4
« Reply #39 on: May 05, 2016, 11:41:21 AM »

davegravy

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Re: coin cell powered R4
« Reply #40 on: May 05, 2016, 11:42:53 AM »
The lowest power mode with stock moteinos is to use the radio as timer by using listen mode with a RSSI thresh of 255. That gets you down to around 1.2uA. I ended up with a combination of listen mode and this low power setup. Essentially I switch to listen mode when I need interactivity and otherwise use the timer.

What timer do you refer to? Some kind of interrupt in listen mode?

Think he's referring to https://lowpowerlab.com/forum/index.php/topic,1617.0.html and https://lowpowerlab.com/forum/index.php/topic,1325.0.html... but a lot of this is still over my head so I could be misunderstanding.
« Last Edit: May 05, 2016, 11:47:41 AM by davegravy »

davegravy

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Re: coin cell powered R4
« Reply #41 on: May 05, 2016, 03:31:45 PM »
Quote
You guys gave me some kind of bug  :o

The lowest power mode with stock moteinos is to use the radio as timer by using listen mode with a RSSI thresh of 255. That gets you down to around 1.2uA. I ended up with a combination of listen mode and this low power setup. Essentially I switch to listen mode when I need interactivity and otherwise use the timer.

What I want to confirm is that 6uA is about the best you can do in an (interactive) listen mode without further amputating the moteino hardware (in my case, removing the flash chip which is according to datasheet is good for another ~1uA).  There's no other software optimizations I should be researching that you know of?


davegravy

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Re: coin cell powered R4
« Reply #42 on: May 05, 2016, 05:09:47 PM »
No.  Re-read reply #37.

Maybe I'm misunderstanding it, but Joe's using a combo of two different listenmode methods

1) with the RSSI_threshold=255, uses 1.2uA but is non-responsive to other nodes (in simple terms it's a less expensive sleep mode than
Code: [Select]
Lowpower.powerdown(SLEEP_8S, BOD_OFF, ADC_OFF)
)

2) responsive listenmode... as per the listenmode_node and gateway examples. i.e you can actually wake the moteino with a transmission burst. This is more expensive. Within this state I'm getting 6uA, and thought I read elsewhere that Joe was reporting 2uA within this mode, so I just wanted to confirm that 6uA is reasonable and I'm not missing some optimizations within this.


TrendSetter

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Re: coin cell powered R4
« Reply #43 on: June 20, 2016, 03:55:50 PM »
Does anyone have any thoughts on the LTC3525 in relation to the other boost regulators mentioned?  I have used them with success and learned of them from the jeenode micros.
I have opted for them over direct battery because of them being able to pull power from a battery that has almost no voltage.  Does that approach have merit?

Felix

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Re: coin cell powered R4
« Reply #44 on: June 20, 2016, 04:17:02 PM »
I really like the LTC3525-5v too, I use them on the PowerShield. They just work and are very low quiescent draw.

perky

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Re: coin cell powered R4
« Reply #45 on: June 20, 2016, 05:34:40 PM »
Does anyone have any thoughts on the LTC3525 in relation to the other boost regulators mentioned?  I have used them with success and learned of them from the jeenode micros.
I have opted for them over direct battery because of them being able to pull power from a battery that has almost no voltage.  Does that approach have merit?

If you're using coin cells you have to watch inrush current when the regulator turns on. This can be a PITA because the internal resistance of coin cells causes the voltage to dip, especially if they're getting close to depletion. The inrush current pulses can be several times the max rated output current of the regulator if you're not careful. It's best to choose a regulator with a separate soft start capacitor if you can, or failing that a high side switch that is aggressively slew rate controlled.
Mark.