Author Topic: Making a lower power Moteino  (Read 19093 times)

Felix

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Making a lower power Moteino
« on: April 20, 2016, 04:06:04 PM »
I do have to agree it would be nice to make something that runs from an (2x)AA source, no regulator, 8mhz internal resonator, super optimized for low power. The gain would be something like going from the current 4uA (Moteino) to under 1uA. Quite doable and something I'd like to make one day.

joelucid

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Re: Making a lower power Moteino
« Reply #1 on: April 20, 2016, 04:32:39 PM »
I wholeheartedly agree. Battery operation is really the sweet spot of the 328p yet to get most out of it you first have to perform a multi-limb amputation on a Moteino. Let go of the regulator and the oscillator plus the flash and add an rtc so users can finally go 'legit' with freq hopping ;)

Felix

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Re: Making a lower power Moteino
« Reply #2 on: April 20, 2016, 08:38:37 PM »
I agree back.
I do need to mention that the regulator is really a sweet feature of the mainstream Moteinos and without which I probably wouldn't be in Moteino-selling business at this point, maybe I'd just be another forgotten 4 year old hackaday post for some cool-but-who-cares-anyway hand assembled SMD board. I have to also say that the regulator is not by far the #1 issue in achieving low power either.

perky

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Re: Making a lower power Moteino
« Reply #3 on: April 21, 2016, 11:08:18 AM »
The reguator is nice as it allows it to be powered from higher voltages, maybe the type could be changed for an LDO that has a lower voltage spec and possibly lower quiescent current? As it stands it would work down to about 2.7V, but alkalines go down to 1V per cell so you'd need one working down to 2V. The AS1360-33-T looks interesting here, it's pin compatible with the MCP1703 in SOT-23 package but works down to 2V with 20V max input voltage and 1.5uA Iq, also has a lower dropout voltage for given current.

http://www.mouser.com/ds/2/588/AS1360_Datasheet_EN_v2-472961.pdf

Mark.

Felix

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Re: Making a lower power Moteino
« Reply #4 on: April 21, 2016, 11:48:44 AM »
The reguator is nice as it allows it to be powered from higher voltages, maybe the type could be changed for an LDO that has a lower voltage spec and possibly lower quiescent current? As it stands it would work down to about 2.7V, but alkalines go down to 1V per cell so you'd need one working down to 2V. The AS1360-33-T looks interesting here, it's pin compatible with the MCP1703 in SOT-23 package but works down to 2V with 20V max input voltage and 1.5uA Iq, also has a lower dropout voltage for given current.

http://www.mouser.com/ds/2/588/AS1360_Datasheet_EN_v2-472961.pdf

Mark.

Nice find. Price hurts though :) it's 3X+ more than the current regulator in small quantities but getting pretty good at 1000X+.
The problem with the HopeRadios (RFM69, 95) is the VDDmin = 2.4V. So that is quite limiting, the lowest AS1360 usable variant is 2.5v.

perky

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Re: Making a lower power Moteino
« Reply #5 on: April 21, 2016, 12:41:24 PM »
I think the RFM69 series have a min VDD of 1.8V according to the spec sheets (RFM69W and RFM69HW).

I'm not sure what you mean that 'the lowest usable AS1360 variant is 2.5V'. LDOs can and generally are used for voltage clamping, if you put a 2.4V input for example into a 3.3V LDO the pass transistor is fully on so the voltage out follows the voltage in, i.e. in that example it would be 2.4V, until it regulates. Therefore you'd choose a 3.3V variant of LDO if you want to restrict your output voltage from ever going above 3.3V. It's important to get one with a low input voltage spec so you know the circuit starts to work (i.e. the pass transistor turns on) at that low voltage.

Mark.

Edit: I notice the voltage range you specifiy for Moteinos is recommended 3.5V to 9V. This will happily work down to 2.7V (assuming the other components also work down to 2.7V).
« Last Edit: April 21, 2016, 12:57:11 PM by perky »

Felix

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Re: Making a lower power Moteino
« Reply #6 on: April 21, 2016, 02:18:19 PM »
The abs minimum for HW is 2.4V. Disregard the Hope datasheets, they are incorrect. There is an RF switch component on the board that limits it to 2.4v, according to its datasheet. It might work below that but its out of spec.
Regardless of that, the W uses the same silicon chip from Semtech, the SX1231h, which is a 2.4v minimum also: http://www.semtech.com/images/datasheet/sx1231h.pdf
See the datasheet for the regulator you referenced, it has fixed output voltages, the closest greater than 2.4v is 2.5v - so that's where I got the 2.5v.
« Last Edit: May 26, 2016, 09:13:54 PM by Felix »

perky

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Re: Making a lower power Moteino
« Reply #7 on: April 21, 2016, 03:03:25 PM »
Well thanks for pointing that out! I'm in the middle of a project that uses 2 cells, I thought I had some headroom so glad I put an ideal diode circuit on it now  :-\

I'm still not sure why you would choose a regulator with a regulated voltage closest to 2.4V, unless you want all the circuit all to run at 2.5V. That means any IO would also be at 2.5V and maybe would make programming and interfacing harder from a logic level point of view.  Putting in a 3.3V LDO with a low minimum working input voltage like the AS1360-33-T would still work down to 2.4V, it would also allow it to be run at 3.3V in 3.3V systems without logic level translation. I don't think there's any power benefit from doing that given the current consumption is a linear thing with voltage and you'd be dropping voltage across the regulator didssipating the power that would have been dissipated in the circuit.

Anyway, the main thing is you've prevented me from making a potentially costly mistake from a production point of you, so thank you!

Mark.

Felix

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Re: Making a lower power Moteino
« Reply #8 on: April 21, 2016, 03:57:51 PM »
I'm still not sure why you would choose a regulator with a regulated voltage closest to 2.4V, unless you want all the circuit all to run at 2.5V.
I thought you wanted to run from 2xAA ?
If you want 3.3v to be in the range of 3.3/5v devices, in that case rather than a LDO you would use a booster with 2xAA which shouldn't be too bad. But you'd want something with at least 200mA output.

perky

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Re: Making a lower power Moteino
« Reply #9 on: April 21, 2016, 04:27:34 PM »
Right, I've been digging into this a little deeper. The Semtech sx1231 can output +13dB and has a minimum voltage limit of 1.8V. The sx1231h has a max output of +20dB (100mW), and a minimum voltage of 2.4V.

Now the RFM69 uses a sx1231h (as confirmed by the version number register which is different to the sx1231). However, the chip is marked RF69, and there is a datasheet for it:
www.orcam.eu/res/Datablad/rf69v12.pdf

This shows that for up to +17dB the voltage can be as low as 1.8V (using PA1 and PA2, normal power settings) . From +17dB to +20dB it uses PA1, PA2 with high power settings and needs 2.4V. So it appears the 2.4V spec is for the full output power using PA1, PA2 and high power settings.

The RFM69CW is restricted to +13dB from the RFIO output, and doesn't use PA1, PA2 or the high power settings, and according to the RF69 datasheet only needs 1.8V. Even though this is missing in the sx1231h datasheet the thing that makes it credible is that the sx1231 is also +13dB without the PA amplifiers and also has a minimum voltage of 1.8V.

Now I'm curious as to what the other 2.4V component is, the RFM69CW and RFM69W have only passives and crystal, unless you're saying it's an oscillator? All the reference designs use a crystal and both pins 4 and 5 of the sx1231h are connected to the device and the other two are ground, so I'm sure it's a crystal.

My conclusion is that the RFM69CW and RFM69W are OK down to 1.8V.
Mark.
« Last Edit: April 21, 2016, 04:34:25 PM by perky »

perky

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Re: Making a lower power Moteino
« Reply #10 on: April 21, 2016, 04:30:46 PM »
Well I'm actually doing an embedded design, it uses 2 alkaline cells to run a micro with a RFM69CW. All logic works down to 2V, no interface to the outside world.
Edit: Except a programming interface and FTDI serial interface for debugging. For that I power via USB, hence there's a STLQ015M33R 3.3V regulator with VBATT as input and micro/radio power as output. The battery input uses an ideal diode circuit so it can be OR'd together with the USB 5V (which uses a pair of diodes in series first to knock it down a bit) to form VBATT. So this stops the internal power supply going over 3.3V, and still allows the battery to drop to 2V or so, and allows 3.3V signalling for programming and debugging.
« Last Edit: April 21, 2016, 05:07:27 PM by perky »

joelucid

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Re: Making a lower power Moteino
« Reply #11 on: April 22, 2016, 01:33:36 AM »
Quote
The abs minimum for HW is 2.4V. Disregard the Hope datasheets, they are incorrect. There is a component on the board that limits it to 2.4v.

Felix, what's the part that prevents use below 2.4v? I have a project using the rfm69hcw where I've gone a bit overboard with battery life optimizations. It runs from a buck converter off of a 9v battery. During sleep I run the board at the lowest possible voltage by only switching the buck on for less than a ms at a time and then coasting down from a 100uF cap.

This results in a vcc profile that starts at 2.3v and coasts down to around 2V. I've found that I can operate the rfm69hcw down to slightly less than 2v that way in rx - at least well enough that I can detect RSSI.

Of course once I do detect a signal I switch on the buck and bring vcc up to 3.3v so I don't have data on tx from that project. I do have some from my coin cell motes (using the rfm69hw) where I have a feature that monitors vcc during the tx cycle and reports the lowest seen voltage to the gw. When I tested that I sent packets at tx levels normally unsuitable for coin cell motes and could also see success with minimum voltages down to around 2v.

Joe
« Last Edit: April 22, 2016, 01:54:54 AM by joelucid »

emjay

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Re: Making a lower power Moteino
« Reply #12 on: April 22, 2016, 05:20:17 AM »
@Joe,

The daughter boards are significantly different in component count between the RFM69(C)W and the RFM69HW.
The crystal is just a two active pin crystal and does not force the lower voltage limit.


joelucid

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Re: Making a lower power Moteino
« Reply #13 on: April 22, 2016, 05:26:53 AM »
Quote
The daughter boards are significantly different in component count between the RFM69(C)W and the RFM69HW.
The crystal is just a two active pin crystal and does not force the lower voltage limit.

I'm aware of that - I use both. But my experience is even the hw/hcw ones work below 2.4v just as spec'd in the hoperf data sheet.

perky

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Re: Making a lower power Moteino
« Reply #14 on: April 22, 2016, 05:33:28 AM »
I think it might be the rf switch, it's the only other component on the reference schematic that could be an active part. Some of those go down to 1.8V. What we could do with if a full BOM of the parts used on both variants, that would sort out the crystal ppm issue too.
Mark.
« Last Edit: April 22, 2016, 05:38:11 AM by perky »