Author Topic: Ultra low power listening mode for battery nodes  (Read 64933 times)

joelucid

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Re: Ultra low power listening mode for battery nodes
« Reply #60 on: July 22, 2015, 12:54:16 PM »
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Well, I was pulling your chain in the previous post, because, as you say, this is not mission critical stuff and you'll get the data on the next cycle. 

Well it did surprise me how large the collision probability turned out to be. So thanks for motivating me to calculate it. I'm looking forward to more real life tests - if we can actually build 5 year thermometers using a cr2032 that'd be pretty cool.

They'll be around 10 Euros each - so you can just plaster your home with them ...

TomWS

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Re: Ultra low power listening mode for battery nodes
« Reply #61 on: July 23, 2015, 09:22:47 AM »
...I'll just cut the response window into n slices and have each node respond during one of them.
Do you mean that each node will have a specific time slot to respond and they'll 'know' when to schedule the time slot based on when they detected the burst (from the counter you're adding)?

Tom

joelucid

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Re: Ultra low power listening mode for battery nodes
« Reply #62 on: July 23, 2015, 12:25:14 PM »
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Do you mean that each node will have a specific time slot to respond and they'll 'know' when to schedule the time slot based on when they detected the burst (from the counter you're adding)?

Yeah that was the idea.

Timing differences in the WDT and internal 8mhz resonator between nodes could be a challenge. To work around that nodes could learn the specifics of their clocks by looking at a couple of burst packages.

Or you just make the slices large enough so that the tolerances don't matter. The farther away from the burst the slice is, the larger the slice needs to be so that the tolerances don't lead to collisions because the larger the accumulated discrepancy between the clocks.


« Last Edit: July 23, 2015, 12:38:55 PM by joelucid »

joelucid

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Re: Ultra low power listening mode for battery nodes
« Reply #63 on: July 24, 2015, 10:49:15 AM »
It's really too bad how little energy you can use with a coin cell and a 200uF cap (and I agree much larger has its own disadvantages). Realistically you get maybe 5ms @ 25mA if you want to be able to run the battery down to 2.6V (idle) for the cap alone. Add a couple of mA for the coin cell.

So 200kbaud seems like a must to me. And for the bootloader it's strictly one request, one response packet. A full app (32k - 4k bootloader) would take 672 packets. Recharge the cap 5x per second and an update will take a bit longer than 2 minutes.

It's too bad because the overall energy expenditure is much larger than necessary due to all those request packets since we can't batch responses.

TomWS

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Re: Ultra low power listening mode for battery nodes
« Reply #64 on: July 29, 2015, 08:53:57 AM »
Well, here's the latest and, I think, the last iteration.  I've tied the Si7021 power (along with I2C pullups) to a GPIO pin and connected CapVSense to A1.  It's interesting that the bulk of the circuitry on this design is dedicated to the moment a battery is inserted into the circuit board  :o

And for the next 'n' months the hardware is idle.  Go figure...

Tom

EloyP

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Re: Ultra low power listening mode for battery nodes
« Reply #65 on: July 29, 2015, 11:10:46 AM »
Probably nothing you guys don't know already but JeeLabs' JCW has just written a post on powering sensors with coin cell batteries:

http://jeelabs.org/2015/07/29/could-a-coin-cell-be-enough/

Very high level but it's a good introduction.

Cheers,

Eloy Paris.-

TomWS

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Re: Ultra low power listening mode for battery nodes
« Reply #66 on: July 30, 2015, 10:28:16 AM »
Here's the battery data from the last 19 days.  This is for the Version 1 prototype and doesn't include my initial, uh, 'mess-ups' in getting the Mote started.  From this data, I wouldn't be surprised if my mess-ups drained off about 50% of the battery's life.  Even in this chart you can see a couple of cases where the gateway was offline and the node was doing multiple retries on sends.  I've since fixed this, as it no longer retries. It sends once, requesting Ack (to get its RSSI feedback), and then goes to sleep.

Tom
« Last Edit: July 30, 2015, 10:33:10 AM by TomWS »

joelucid

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Re: Ultra low power listening mode for battery nodes
« Reply #67 on: July 31, 2015, 04:58:14 PM »
What's the update frequency?

TomWS

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Re: Ultra low power listening mode for battery nodes
« Reply #68 on: August 01, 2015, 12:00:54 AM »
What's the update frequency?
TH sampling occurs once per 10 minutes (based on Mote internal RC 8MHz clock).  Async push to the Gateway.  Mote status update (battery and transmit levels) occurs every 6 samples (once per hour).

Tom

ulli

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Re: Ultra low power listening mode for battery nodes
« Reply #69 on: August 07, 2015, 12:57:00 PM »
Hi,

I currently also work on a new circuit design to further reduce the power consumption of my battery powered moteino. I plan to do something similar with Toms circuit a few replies above.

I understood your posts in that why, that a more or less constant current consumption results in better battery life than current peaks  caused by the Listening Mode or frequently transmissions.
--> So, the target is to make the current consumption as smooth as possible with a well defined cap, which buffers the transmissions and listening mode current peaks?

What do you think about using the IRLML6402 Mosfet instead of SI2365? (No supplier is available which makes sense for me)
It has a very low on resistance and should work with 3.3V on/off.
http://www.irf.com/product-info/datasheets/data/irlml6402.pdf

Am I right?

TomWS

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Re: Ultra low power listening mode for battery nodes
« Reply #70 on: August 07, 2015, 02:12:06 PM »
Hi,

I currently also work on a new circuit design to further reduce the power consumption of my battery powered moteino. I plan to do something similar with Toms circuit a few replies above.

I understood your posts in that why, that a more or less constant current consumption results in better battery life than current peaks  caused by the Listening Mode or frequently transmissions.
--> So, the target is to make the current consumption as smooth as possible with a well defined cap, which buffers the transmissions and listening mode current peaks?

What do you think about using the IRLML6402 Mosfet instead of SI2365? (No supplier is available which makes sense for me)
It has a very low on resistance and should work with 3.3V on/off.
http://www.irf.com/product-info/datasheets/data/irlml6402.pdf

Am I right?
Assuming your power supply is at least 3V, then, yes, that MOSFET will be fine.  It's too bad the data sheet doesn't show the drain current vs Vgs at lower currents, but it appears to be more than enough for this application.

If you can fit a larger cap than I used, it would be much much better.  200uF is really not enough to isolate the pulsed load from the battery and I can see 40mA spikes at the battery when the RFM69W is transmitting at full power (my code automatically dials back the transmit level, but this is the worst case condition). 

In the scope trace below, you can see the blue trace is the CR2032 which starts at 3.0V but then falls to about 2.4V during the transmit (and recovery) time while the yellow trace is across the 200uF cap & RFM69W falls below 2.0V.  The purple trace is the difference of the two voltages across a 10 ohm resistor, 400mV or 40mA.  It's brief and the battery recovers quickly, but if you can use a supercap or, at least, something substantially larger than 200uF you'd be better off.  Of course, I'm using the same coin cell that I've been abusing for weeks so I'm not sure how a fresh one will behave.  This one keeps on working and I'll keep abusing it until it stops  :D

In any case, I'm happy with the circuit and have sent it to OSH Park for fab.  I'll let you know (and post the design files) when I have the PCB running (probably within two weeks).

Tom





ulli

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Re: Ultra low power listening mode for battery nodes
« Reply #71 on: August 09, 2015, 07:14:31 AM »
Thats a good point. I am using 2x AA batteries which should work down to 1.8V due to the limit of the RFM Module and the Atmega.
Addi tonally the capacitor have to be way bigger than I thought before to also provide enough energy for the transmission. -> voltage drop must be minimized.
Do you think the Mosfet will also work with 1.8V. The Datasheet shows a VGS(max) of 1.2V...Doesn´t it mean that I can use it down to 1.2V control voltage of the Gate?

Looking forward to your final design and test results.

TomWS

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Re: Ultra low power listening mode for battery nodes
« Reply #72 on: August 09, 2015, 09:34:24 AM »
Thats a good point. I am using 2x AA batteries which should work down to 1.8V due to the limit of the RFM Module and the Atmega.
Addi tonally the capacitor have to be way bigger than I thought before to also provide enough energy for the transmission. -> voltage drop must be minimized.
Do you think the Mosfet will also work with 1.8V. The Datasheet shows a VGS(max) of 1.2V...Doesn´t it mean that I can use it down to 1.2V control voltage of the Gate?

Looking forward to your final design and test results.
Ulli, if you're using AA batteries  then you don't need the switches. Your mote will power up without any problem.  The switches and caps are there to limit the power surge to a coin cell battery which doesn't deal well with the high current surge. AA will literally last for years.  Basically the shelf life of the battery.

Tom

Felix

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Re: Ultra low power listening mode for battery nodes
« Reply #73 on: August 09, 2015, 08:27:33 PM »
Thats a good point. I am using 2x AA batteries which should work down to 1.8V due to the limit of the RFM Module and the Atmega.
Don't count on the RFM HW boards from HopeRF to go down to 1.8V as claimed in the datasheet. The fact is that the switcher they use is a 2.4V GaAs device (the SC70 chip). So only the RFM69-W which don't have that part will probably be reliable down to 1.8V. On the RFM69HW you probably don't care anyway since it's a 100mW TX device and you use it for the power not for saving the battery to the absolute maximum.

ulli

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Re: Ultra low power listening mode for battery nodes
« Reply #74 on: August 13, 2015, 03:54:07 PM »
This is an interesting question since if the pulsed load hurts it would make sense to put a resistor in front of the load. This might make sense anyway since it would cause the system to restart if it gets stuck in receive etc instead of damaging the battery. I'm currently running a test to verify this.

Sorry for the late feedback...
As already stated, I use 2xAA batteries. I further need to reduce the power consumption due to a current module lifetime of only 3 month in ListenMode with a few infrared transmissions.
You are right that I do not need the cap for limiting the power surge/voltage drop like it is on a coin cell battery.
I am thinking about your cap solution with an additional series resistor to reduce the current peaks. I think current peaks(Listen 4µA -> RX 25mA) reduces the lifetime of a AA battery, doesn´t it?