A boost DC-DC converter can do the job with 2 Alkaline AA's. Buck boost converters are more practical since you might want to also use a non-battery power source like USB power or other cheap DC supply for project development.
Not sure, but a single CR123A 3V LIPO might power propeller for most of the battery life.
Back in the "olden days" the stepup converters using two batteries always worked better than with just one. That may not be true now, but still, with two batteries you might be using nicads so 1.5V is really on average 1.2V and it might drop to 1V. I think there was the idea also that 2 batteries "died" better than, say 3 batteries. With three batteries, one could go reverse voltage which is really bad for rechargeables. But with two batteries, if one cell went flat, the whole stepup controller died, which protected the other cell from reverse voltage.
Bottom line is that two cells work very nicely.
As jazzed has pointed out, we now have LiPos. And while one LiPo needs more care (you must never let them go flat), you only need one cell. Send it through a buck/boost to produce a reliable 3.3V, and it could be a very nice solution.
There must be some "perfect" chip out there. Input 1V to >5V and output regulated 3.3V
Disable the brownout detector, add a pullup to the reset line, only run at 40MHz or less and directly wire to the battery. It may run faster, haven't gotten around to testing the exact speed limits. Prop should be happy even below 2 volts. If you're really worried about brownouts, a MN1381 or similar chip can be hooked to reset the chip below 1.8-2 volts. First link in my signature shows my experiments on this. I've successfully programmed a Prop while it ran at 1.6v so the maximum clock at 1.6v is faster than RCFAST.
I created a prop-based remote control that runs for months on 2 AA's (not rechargeables).
It's able to do this because it spends almost all of the time in a slow clock/waitcnt state. Only when a button is pressed does it actually switch to the crystal.
At about 2.7V the unit no longer functions properly. That, however, may be because there's not enough ooomph and/or high enough voltage left in the batteries to power the IR led.
I created a prop-based remote control that runs for months on 2 AA's (not rechargeables).
It's able to do this because it spends almost all of the time in a slow clock/waitcnt state. Only when a button is pressed does it actually switch to the crystal.
At about 2.7V the unit no longer functions properly. That, however, may be because there's not enough ooomph and/or high enough voltage left in the batteries to power the IR led.
Walter
2.7v is the on chip brownout detector's threshold. Tie the BOEn pin high to turn off the brownout detector. Also put a pullup on RESn so static won't reset the Prop. The remote should now run until the AA's are dead and/or the IR LED is too dim for the receiver to see.
All this really depends on what the prop is doing and driving. Boosting is used in the single battery solar garden lamps, although this is usually a crude cct.
The batteries also have to power the Nordic nRF24L01+, which has a very low power mode that can be enabled. The Nordic can operate from 1.9V - 3.6V. Other than a few passives, that's all there is to it.
If you need the Nordic to remain on and receiving, it will draw about 17mA.
If you could have the device awakened with a button press, then the Prop could power the Nordic directly with an I/O pin (this usually requires an extra cap on the Nordic's Vdd pin).
Since you are using this with a wireless device, you'll need to be careful about using a switching regulator.
Mike Green has suggested ways of shielding a switching regulator but my initial (halfhearted) attempts haven't worked well.
They sell Li-Ion in AA sizes. You'd need to include a warning on both the batteries and the device about the voltage difference of the cells.
I'm not sure if the danger of using the Li-Ion AAs in some other device or someone using normal AAs instead of the Li-Ion in your device outweigh the convenience of using AA cell holders.
A single Li-Ion (of LiPo) seems to be outside the usual input voltage range of buck regulators. It seems like there are more options for regulating two Li-Ions to 3.3V than one.
Two alkaline AAs are probably a better solution in many cases than trying to regulate the higher voltage Li cells but I just don't like non-rechargeable batteries.
AA size lithium iron disulfide primary cells (Energizer L91, also clones from batteryspace.com), have "normal" 1.5V and a nice discharge curve, lightweight, and good at extreme temperatures.
Remember that both the buck/boost regulators, and any "normal" regulators that
regulate from a higher voltage down to a lower one, may have vastly more "idle"
current draw than a base prop in a "wait" condition with the PLL off.
That is, two AA cells directly to prop VCC, with the pin connections described
above to prevent brownout, may well last much longer than *anything* using a
buck, boost, buck-boost, or linear. This will probably be true both for lithium
and alkaline, even despite alkaline's voltage sag with age.
The simplicity, too, is extremely attractive.
So we need an EEPROM, a Prop chip, a resistor, two batteries, and you've
already got something that works (probably). If you add a crystal you might
also want to add a small cap at VCC.
It would be interesting to see how long such a setup could blink an LED. If the
on period was short, it could be months.
This is true; the regular lonesock points out is amazing to me.
I'm so used to seeing regulators that have several (or even ten) milliamps of "idle" current draw.
The one lonesock shows has a "typical" off current draw of 0 microamps, and max of 2 microamps.
That's pretty fantastic.
I'm not sure what the current draw is when "on" but the load is drawing only microamps.
Tracy: Thanks for posting that curve. I have never bothered to look before. It certainly makes using 2x Lithium AA an excellent choice for powering a prop+cct that has a low power requirement.
At 50mA draw and operational to 2.8V would give ~50 hours use.
That buck regulator with "inductor-imbedded ferrite" is quite interesting, but I wouldn't consider it either for a micropower design. The 2µA figure applies only to shutdown, and the best guess at performance under load comes from the efficiency curves.
It is remarkable for a buck regulator to be spec'd down as low as 1mA, but the efficiency may(?) drop like a rock as it approaches the quiescent current.
Some switching regulators that advertise low quiescent current like 20µA achieve that by going into a burst mode when the demand is low. But even so, it can match the quiescent current of running directly from a battery or with a linear regulator like the MCP17xx series.
Yea, that regulator Lonesock linked is amazingly small. Eyeballing it off the efficiency charts I'd estimate it's idle current between 100 and 200 microamps. The best idle current's I've see for switching regulators have been with LTI's "burst mode" chips. The Buck-Boost LTC3530 idles at ~40uA, while many of LTI's Buck regulators idle in the <10uA range. (just one example is LTC1771 ) For Linear regulators the Micrel MIC5232 is the best I've found. <2uA idle current even in dropout or when the input is disconnected while the load still has power.
For very low idle currents there's also the MAX1722(..23, ..24). Step-up in SOT23-5 package, only additional parts are the input, output capacitors and the inductor.
Let me ask you guys about an idea I have in mind. I do not know what would be the best circuit but here is the idea. If the device does not need to do anything until some event triggers a pin on the Propeller, what if the code had a circuit in which if a button was pressed that took the vss of the Prop board to GND, the power was allowed to boot because it now has power. Upon power up, the code engages a pin which completes a path to VSS for the board by some means. I don't want a relay nor the power to keep a relay on. But what about an n channel transistor or mosfet that stayed on while the pin was high. After an hour of inactivity (no activity on a pin or data), the Prop turned off the pin and thusly kills VSS to the board. The condition is that it is OK if the user knows that after a timeout, that a button press would have to wake up the board, then it would work fine again, the Prop resetting the timer after each event so that there is an hour of ready mode before sleep.
Have you seen this thread? It has some ideas on how to have the Prop control its own power.
A latching relay doesn't require power to stay on or off. It just uses current to change states. I don't think a latching relay is as elegant as the solutions on the other thread, but I kind of understand how latching relays work so I'd be inclined to use one myself.
It's been a while since I've read the thread I linked to so I don't remember if the solutions were low power or not. I think a latching relay could be latched on with a button press and then the Prop could latch it off when desired. The latching relays I've used were about 1/2" x 3/8" x 3/16". There are a lot of these little relays that can be driven directly by a Propeller.
T Chap
Posts: 4,223
Comments
Though the extra cost offset the cost of a 3rd battery, but if space and not using an oddball number of batteries is preferred.
http://www.mouser.com/ProductDetail/ON-Semiconductor/NCP1450ASN33T1G/?qs=%2fugrpAKHX8r8z5O2syl402rCowfjQeLPBWesZNM0YqQ%3d
or with built-in switching mosfet.
http://www.mouser.com/ProductDetail/Texas-Instruments/TPS61097-33DBVT/?qs=IK5e5L0zOXj92STPEaYJfzfQKLzHq0fPPQnSK%2fMpEbs%3d
A lot easier to use 3 AAA...
But, if you really need to... Sparkfun has a few DC-DC converter that take AA batteries, last time I looked...
A boost DC-DC converter can do the job with 2 Alkaline AA's. Buck boost converters are more practical since you might want to also use a non-battery power source like USB power or other cheap DC supply for project development.
Not sure, but a single CR123A 3V LIPO might power propeller for most of the battery life.
Bottom line is that two cells work very nicely.
As jazzed has pointed out, we now have LiPos. And while one LiPo needs more care (you must never let them go flat), you only need one cell. Send it through a buck/boost to produce a reliable 3.3V, and it could be a very nice solution.
There must be some "perfect" chip out there. Input 1V to >5V and output regulated 3.3V
Disable the brownout detector, add a pullup to the reset line, only run at 40MHz or less and directly wire to the battery. It may run faster, haven't gotten around to testing the exact speed limits. Prop should be happy even below 2 volts. If you're really worried about brownouts, a MN1381 or similar chip can be hooked to reset the chip below 1.8-2 volts. First link in my signature shows my experiments on this. I've successfully programmed a Prop while it ran at 1.6v so the maximum clock at 1.6v is faster than RCFAST.
Lawson
T Chap -
I created a prop-based remote control that runs for months on 2 AA's (not rechargeables).
It's able to do this because it spends almost all of the time in a slow clock/waitcnt state. Only when a button is pressed does it actually switch to the crystal.
At about 2.7V the unit no longer functions properly. That, however, may be because there's not enough ooomph and/or high enough voltage left in the batteries to power the IR led.
Walter
Regulator (4.1 to 15VDC) or Boost converter (1.4 to 3.6VDC) can be used.
The design is on Tubular's smorgrasboard panel.
2.7v is the on chip brownout detector's threshold. Tie the BOEn pin high to turn off the brownout detector. Also put a pullup on RESn so static won't reset the Prop. The remote should now run until the AA's are dead and/or the IR LED is too dim for the receiver to see.
Lawson
If you could have the device awakened with a button press, then the Prop could power the Nordic directly with an I/O pin (this usually requires an extra cap on the Nordic's Vdd pin).
Since you are using this with a wireless device, you'll need to be careful about using a switching regulator.
Mike Green has suggested ways of shielding a switching regulator but my initial (halfhearted) attempts haven't worked well.
They sell Li-Ion in AA sizes. You'd need to include a warning on both the batteries and the device about the voltage difference of the cells.
I'm not sure if the danger of using the Li-Ion AAs in some other device or someone using normal AAs instead of the Li-Ion in your device outweigh the convenience of using AA cell holders.
A single Li-Ion (of LiPo) seems to be outside the usual input voltage range of buck regulators. It seems like there are more options for regulating two Li-Ions to 3.3V than one.
Two alkaline AAs are probably a better solution in many cases than trying to regulate the higher voltage Li cells but I just don't like non-rechargeable batteries.
LXDC2HL33A-055
Jonathan
regulate from a higher voltage down to a lower one, may have vastly more "idle"
current draw than a base prop in a "wait" condition with the PLL off.
That is, two AA cells directly to prop VCC, with the pin connections described
above to prevent brownout, may well last much longer than *anything* using a
buck, boost, buck-boost, or linear. This will probably be true both for lithium
and alkaline, even despite alkaline's voltage sag with age.
The simplicity, too, is extremely attractive.
So we need an EEPROM, a Prop chip, a resistor, two batteries, and you've
already got something that works (probably). If you add a crystal you might
also want to add a small cap at VCC.
It would be interesting to see how long such a setup could blink an LED. If the
on period was short, it could be months.
I'm so used to seeing regulators that have several (or even ten) milliamps of "idle" current draw.
The one lonesock shows has a "typical" off current draw of 0 microamps, and max of 2 microamps.
That's pretty fantastic.
I'm not sure what the current draw is when "on" but the load is drawing only microamps.
At 50mA draw and operational to 2.8V would give ~50 hours use.
It is remarkable for a buck regulator to be spec'd down as low as 1mA, but the efficiency may(?) drop like a rock as it approaches the quiescent current.
Some switching regulators that advertise low quiescent current like 20µA achieve that by going into a burst mode when the demand is low. But even so, it can match the quiescent current of running directly from a battery or with a linear regulator like the MCP17xx series.
Lawson
A latching relay doesn't require power to stay on or off. It just uses current to change states. I don't think a latching relay is as elegant as the solutions on the other thread, but I kind of understand how latching relays work so I'd be inclined to use one myself.
It's been a while since I've read the thread I linked to so I don't remember if the solutions were low power or not. I think a latching relay could be latched on with a button press and then the Prop could latch it off when desired. The latching relays I've used were about 1/2" x 3/8" x 3/16". There are a lot of these little relays that can be driven directly by a Propeller.