Author Topic: Making a lower power Moteino  (Read 20550 times)

WhiteHare

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Re: Making a lower power Moteino
« Reply #75 on: October 01, 2016, 09:16:06 AM »
One big problem with boost regulators is their start-up current, it can cause a current spike of several hundred mA if you're not careful. This is a problem when batteries are depleted because their internal resistance shoots up, a large current spike will drop the voltage to below the working threshold which will necessarily require the end point of the batteries to be higher . So you need some kind of slew rate control on the output of the boost regulator, or a programmable soft start.
Mark.
Are there any boost chips that come with that kind of spike avoidance already built into them?  It would be handy to have a "go to" chip for those sensors that might need to run for short duration but at higher minimum voltages like 3.3v or 5v.  Even just knowing the proper keyword to look for would help in maybe finding something applicable in, say, Linear Technology's catalog of boost converters (of which there are many different types so as to cover a whole gamut of different use cases).
« Last Edit: October 01, 2016, 09:45:47 AM by WhiteHare »

perky

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Re: Making a lower power Moteino
« Reply #76 on: October 01, 2016, 12:17:56 PM »
You can search for soft start external capacitor boost regulators, one such part is the ADP1612 that has an external cap:
http://www.farnell.com/datasheets/1793793.pdf

Note that a lot of boost regulators have a DC path from Vin through the inductor and the diode to Vout so they need a load switch on the front of it too if you want to isolate completely.

Some useful stuff:
http://www.analog.com/library/analogDialogue/archives/45-09/boost.html

Mark.

MoebiusL

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Re: Making a lower power Moteino
« Reply #77 on: October 02, 2016, 11:32:30 AM »
Good inputs, I just checked and the board I'm doing some trials uses a MCP16251 boost, just checked the datasheet and it has built-in soft-start (typical 1.5ms) and regulates the output via PWM and PFM depending on the required current, which seems to optimize the performance for small and larger currents.

Regarding the TMP36, that's just a test sketch. On other projects I need to have some voltage over 3.0V because of an ultrasonic sensor (US-100), etc. So going much lower without regulator limits too much the possibilities. I'll indeed try the lithium cells, shame they still a bit pricey. The conclusion I got is that's difficult to find a fit-all size when talking about low-power, you basically need to adapt the board for each situation.

perky

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Re: Making a lower power Moteino
« Reply #78 on: October 02, 2016, 12:38:06 PM »
The choice of boost mode of operation is quite important. The MCP16251 for example uses a scheme where the current ramps up to a certain max value then turns off which pumps that energy into the ouput, this max current limit value is designed for maximum output current and is usually about twice the maximum output current so even though the max current is limited to 100mA during the startup it can still take large current spikes when it is regulating (see figure 2-21 of the MCP16251 datasheet that shows even with 15mA output current the peaks are still 250mA or so).

So if you really want to reduce spikes to a minimum the best option is to choose a regulator that you can also control the maximum peak current. For example, the NCP1406 uses a max ON time scheme of 0.9us, it will turn off ramping up the current through the inductor if it either reaches its max current, or after 0.9us. This allows you to put larger value inductors in (which have a slower ramp) and effectively control the peak current through the inductor, and hence also through the input. You may for example only need 15mA of output current so you don't really want 250mA pulses at a low pulse rate if you can avoid it.

There's still a problem with the current ramping up at startup even with the NCP1406 with its soft start (3ms typical) and it's not isolated, so I put a slew rate controlled load switch on the front of mine as well. BTW I probably wouldn't use the ADP1612 for those reasons too, that shows an external cap for slew rate control but is quite a beefy chip for low current solutions.

Mark.

steve v

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Re: Making a lower power Moteino
« Reply #79 on: October 04, 2016, 09:24:10 PM »
Does anyone have a simple / lowest labor solution to bypassing the Linear Regulator on the Moteino ?
I plan on running an RFM95 Moteino with a pair of Lithium L91 AA batteries and I think it makes sense to take the regulator out of the equation.

Do I need to remove the device, and solder a bridge ? or Just add a jumper wire somewhere ?

TomWS

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Re: Making a lower power Moteino
« Reply #80 on: October 04, 2016, 11:14:06 PM »
Does anyone have a simple / lowest labor solution to bypassing the Linear Regulator on the Moteino ?
I plan on running an RFM95 Moteino with a pair of Lithium L91 AA batteries and I think it makes sense to take the regulator out of the equation.

Do I need to remove the device, and solder a bridge ? or Just add a jumper wire somewhere ?
IMO, if you're not using the VR, take it out.  It's easy to do (hint, lift single leg side first, then each of the other two).  I have a 'drawer' full of MCP1703s taken off Moteino boards that I use elsewhere - thanks, Felix!

Tom

steve v

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Re: Making a lower power Moteino
« Reply #81 on: October 15, 2016, 02:31:32 PM »
Thanks Tom,

I found I could remove the regulator with a wire snipper  and then power the Moteino from the 3.3V pin.   My board stops running at 2.81V

Does it make sense to reconfigure the Moteino 328P to  run below the 2.81 V,  any suggestions on how to do this ? I don't see any sketch examples for this ?  Or is this a fuse configuration ?

TomWS

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Re: Making a lower power Moteino
« Reply #82 on: October 15, 2016, 06:45:31 PM »
Thanks Tom,

I found I could remove the regulator with a wire snipper  and then power the Moteino from the 3.3V pin.   My board stops running at 2.81V

Does it make sense to reconfigure the Moteino 328P to  run below the 2.81 V,  any suggestions on how to do this ? I don't see any sketch examples for this ?  Or is this a fuse configuration ?
If you want to run reliably below 3.3v you'll need to change the fuses. The first change is the oscillator source - that will need to change to 8mhz or less.  Also check the BOD settings.  They should be set off or below 2.7V if you're going to run close to that.
Tom

curious

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Re: Making a lower power Moteino
« Reply #83 on: September 13, 2017, 04:20:04 PM »
Actually I run a project which builds Moteino compatible clones without voltage regulator @ https://www.canique.com

The problem with an Arduino Mini Pro e.g. or a standard Moteino is that if you run it with low voltages, you have high current consumption. E.g. a standard moteino will draw ~55uA @ 2.4V because of the voltage regulator.
A voltage regulator only makes sense when running above 3.3V.

Felix

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Re: Making a lower power Moteino
« Reply #84 on: September 15, 2017, 05:08:59 PM »
Actually I run a project which builds Moteino compatible clones without voltage regulator @ https://www.canique.com

The problem with an Arduino Mini Pro e.g. or a standard Moteino is that if you run it with low voltages, you have high current consumption. E.g. a standard moteino will draw ~55uA @ 2.4V because of the voltage regulator.
A voltage regulator only makes sense when running above 3.3V.

Awesome rebadge :)

Hey folks BTW I just released the vanilla Moteino with no-LDO, this batch has been sitting on my desk for about 6 weeks, just one of those things that get back burner-ed unintentionally. Sorry ChemE and other enthusiasts who have been asking for this variant.

mielleriealphonse

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Re: Making a lower power Moteino
« Reply #85 on: November 11, 2017, 05:00:26 AM »
Great Hacking of your own material ! Like it !

I am facing the challenge of having solar battery for one project. To solve that in a pratical and simple way I have decided to design a solar power supply feedding a small 600mAH LiFePo4. (3.2V) with a very small solar panel of 5V. This type of battery is a good choice to have the full power of RFM module and to have a very stable Voltage and most probably a long life (expecting 10 years).

Of course Moteino LDO need to be remove like in the vanilla version !