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.
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 ?
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.
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 think it might be the rf switch
With a magnifying glass.And young eyes!
The switch only exists in the rfm69hw, not on the w. So I think the w likely runs down to 1.8v. The hw can't switch the high power pa onto the antenna below 2.5v. It still can receive below. It could also send using the low power pa. And it could tx at high power as long as the voltage at the beginning of tx is >2.5v.Unfortunately, the RFM69 design does not permit using PA0. It would be great if it did (you would have full power output range), but it doesn't. If you want to TX, you need, at a minimum, PA1 turned on.
The last one of these is important for coin cell motes. There will likely work even though voltage will go under 2.5v during tx since in the beginning voltage is pretty high.
Unfortunately, the RFM69 design does not permit using PA0. It would be great if it did (you ;) would have full power output range), but it doesn't. If you want to TX, you need, at a minimum, PA1 turned on.
@Felix Looking at the datasheet, it only gives the recommended operating voltage range for 25C. I don't see any graphs showing the effects of different temperatures. Do you have any info as to how sensitive those numbers are to temperature?Unfortunately no, I don't have more than what the datasheet reveals. :-\
Felix, have you ever tried to use a RFM69HW at less than 2.5V or is the assumption that it doesn't work based on the data sheet alone?Not that I can remember.
Funny how perspectives change. In the face of uncertainty, keeping the LDO and running from a 9-volt battery "just to be sure" suddenly looks like an attractive, compact, and rational choice if running an HW.... I don't really feel like running a ton more experiments just to test whether the datasheet might be wrong.
Well lets not jump to conclusions. I'm running a test now: RFM69HW on two aa Eneloops with 3 Ohm in parallel.
Apr 22 22:03:18 espgw.lx [11] [RX_RSSI:-36,1,8,45]
Apr 22 22:03:18 espgw.lx test4 -> nd:11,nr:285,pw:12,vc:170,rt:3
Apr 22 22:03:21 espgw.lx [11] [RX_RSSI:-37,1,8,45]
Apr 22 22:03:21 espgw.lx test4 -> nd:11,nr:286,pw:12,vc:170,rt:3
Apr 22 22:03:24 espgw.lx [11] [RX_RSSI:-35,1,8,45]
Apr 22 22:03:24 espgw.lx test4 -> nd:11,nr:287,pw:12,vc:170,rt:3
Apr 22 22:03:27 espgw.lx [11] [RX_RSSI:-36,1,8,45]
Apr 22 22:03:27 espgw.lx test4 -> nd:11,nr:288,pw:12,vc:170,rt:3
Apr 22 22:03:30 espgw.lx [11] [RX_RSSI:-35,1,8,45]
Apr 22 22:03:30 espgw.lx test4 -> nd:11,nr:289,pw:12,vc:170,rt:3
Apr 22 22:03:33 espgw.lx [11] [RX_RSSI:-38,1,8,45]
Apr 22 22:03:33 espgw.lx test4 -> nd:11,nr:290,pw:12,vc:170,rt:3
Apr 22 22:03:36 espgw.lx [11] [RX_RSSI:-35,1,8,45]
Apr 22 22:03:36 espgw.lx test4 -> nd:11,nr:291,pw:12,vc:170,rt:3
Apr 22 22:03:39 espgw.lx [11] [RX_RSSI:-35,1,8,45]
Apr 22 22:03:39 espgw.lx test4 -> nd:11,nr:292,pw:12,vc:170,rt:3
Apr 22 22:03:45 espgw.lx [11] [RX_RSSI:-38,1,8,45]
Apr 22 22:03:45 espgw.lx test4 -> nd:11,nr:294,pw:12,vc:169,rt:17
Apr 22 22:03:51 espgw.lx [11] [RX_RSSI:-38,6,8,45]
Apr 22 22:03:51 espgw.lx test4 -> nd:11,nr:296,pw:12,vc:169,rt:30
Apr 22 22:03:54 espgw.lx [11] [RX_RSSI:-37,1,8,45]
Apr 22 22:03:54 espgw.lx test4 -> nd:11,nr:297,pw:12,vc:169,rt??.
Apr 22 22:04:00 espgw.lx [11] [RX_RSSI:-38,1,8,45]
Apr 22 22:04:00 espgw.lx test4 -> nd:11,nr:299,pw:12,vc:169,rt:33
Apr 22 22:04:06 espgw.lx FreeHeap: 17440
Apr 22 22:04:06 espgw.lx [11] [RX_RSSI:-38,1,8,45]
Apr 22 22:04:06 espgw.lx test4 -> nd:11,nr:301?test4 -> ??#014?B?00?WZ6Q^??
Apr 22 22:04:12 espgw.lx [11] [RX_RSSI:-36,1,8,45]
Apr 22 22:04:12 espgw.lx test4 -> nd:11,nr:303,pw:12,vc:169,rtNYV
Apr 22 22:04:15 espgw.lx [11] [RX_RSSI:-36,1,8,45]
Apr 22 22:04:15 espgw.lx test4 -> nd:11,nr:304,pw:12,vc:169,rtNYV
Apr 22 22:04:43 espgw.lx [11] [RX_RSSI:-38,6,8,45]
Apr 22 22:04:43 espgw.lx test4 -> nd:11,nr:313I?ج?"?A?k???t]#021
Apr 22 22:04:46 espgw.lx [11] [RX_RSSI:-35,6,8,45]
Apr 22 22:04:46 espgw.lx test4 -> nd:11,ns:314,pw:12,vc:168,rt???F
Apr 22 22:04:55 espgw.lx [11] [RX_RSSI:-35,6,8,45]
Apr 22 22:04:55 espgw.lx test4 -> nd:11,ns:317?-r:2??#006?#6???.
Apr 22 22:04:55 espgw.lx [11] [RX_RSSI:-36,1,8,45]
Apr 22 22:04:55 espgw.lx test4 -> nd:11,ns:317?o*'`???#013\??!?|a#021??K
RSSI pretty much unchanged at -36 vs -34 at 2.2V.But, but... RSSI of -36? Were these two devices like right next to each other? What's the behavior when the starting RSSI is -54? Or a more realistic -64? AGC can mask a wide range of sins.
So I guess this should put the hypothesis that the rfm69hw only works down to 2.5V to a conclusive rest.
We should split this topic, what's a good starting post to do that?
What are the benefits of the atmega328pb over 328p ?
Felix, I'll have more on the other items later. Just quickly: the am1815 is broadly sold by Abacon as ab1815. Digikey, mouser etc all carry it. It's fairly inexpensive and VERY low power.Doh, I just searched to AM1815 so of course I got nothing. AB1815 reveals it (http://www.digikey.com/product-detail/en/abracon-llc/AB1815-T3/535-11936-1-ND/3661487). Thanks for pointing that out. At $1.95 (1qty) it's quite a pricey part compared to other things. The required crystal (http://www.digikey.com/product-detail/en/abracon-llc/ABS07-120-32.768KHZ-T/535-11937-1-ND/3724046) adds another $0.70.
- We should also start talking about battery.
- We should also start talking about board format, layout, pinout, perhaps battery connections depending on the battery.
- We should also start talking about programmability (ISCP, FTDI) and powering it when attached to a FTDI. I am thinking it should only be able to work when its own power supply is attached (ie battery), since the 5V from FTDI will fry it (no regulator).
- the FTDI also has a 3.3v power output (via solder jumper) but it's limited to 50mA so that won't do it either.
I echo what others have suggested especially the RTC and Si7021 although the HTU21D has a lower sleep current if the datasheet is to be believed.
For projects I see myself taking on running for 2 decades outweighs being easily swallowed so I prefer to run off 2xAAA rather than a coin cell.
An arduino+radio that can run on 2xAAA for 10+ years and fits in your mouth; surely that would sell.
PS thanks for the lightning fast processing and shipping of my two TPL5110s!
That's why I'm doing some experiments using step-up regulator options, to try to extract as much as possible from the Alkaline AAs even if it cost extra 1uA or 2uA during the sleep. But at the end I'm getting a stable 3.3V all the way down to 0.8V on a single cell (I hope, as the tests still running).I would opt for Lithium AAs rather than Alkaline and a voltage converter as you'll get useful voltage to the end of life without conversion inefficiency and much better low temperature performance.
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.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).
Mark.
Does anyone have a simple / lowest labor solution to bypassing the Linear Regulator on the Moteino ?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!
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 ?
Thanks Tom,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.
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 ?
Actually I run a project which builds Moteino compatible clones without voltage regulator @ https://www.canique.com (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.