Can the Prop run from a coin cell?

Tubular

Has anyone successfully run the prop from a 3v coin cell (CR2032, CR2430 etc)? I'm worried about getting past the initial boot phase, after that the clock can be slowed.

I'm interested for two reasons - 1) an ultra portable design and 2) revisiting PhiPi's suggestion of programming (and possible energy harvesting) via an audio interface (iPod, cell phone here we come)

tubular

mctrivia

I have run 1 of my propmod-us_ps off a coin cell. But that uses a boost converter. Have not tried with just the bstteryl

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
propmod_us and propmod_1x1 are now in stock. Only $30. PCB available for $5

Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.

Mike Green

The initial boot phase only needs one cog which uses the RCFAST clock. The other 7 cogs are stopped and taking minimal power. I don't have the Propeller datasheet handy, but that would have the current drain on it.

The main problem I see with running off a coin cell is that the nominal voltage supplied is already below the normal operating voltage of the Propeller. If you add a diode or even a saturated transistor's voltage drop, you're well below 3V. You'd need the diode or transistor to switch over between the coin cell and whatever other power source you're using. It might be better to use a buck/boost regulator to supply 3.3V from whatever source is available. That would allow for input voltages from 2.7V or lower to 5V or higher.

mctrivia

My buck boost adapter does 1.8-5.5 in.

You can do switch over with lower drop by using mosfet. If you really don't want a power supply.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
propmod_us and propmod_1x1 are now in stock. Only $30. PCB available for $5

Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.

localroger

As Mike Green points out initial boot is one cog on RCFAST, which shouldn't draw more than a couple of milliamps. Any application that does anything will draw more once the EEPROM is sucked and the real code is launched.

Also, button cells tend to be pretty good about supplying high current when it's needed. They can get hot enough to start a fire if you short the out in the presence of something that burns.

FearTurtles

Cant the prop handle as little as 2.7v?

Tubular

Thanks for the replies. It sounds plausible.

@mike the datasheet indicates 2-2.4mA during boot. The sanyo datasheet doesn't tell me a lot about the internal resistance when pulling a few mA, though for a CR2430 it does indicate 6mA continuous can be drawn (I'll have to experiment to see how far it dips down under load)

@mctriv, the boost may be a good option. This design calls for minimal components so I'm going to try without it initially and see what can be done. If need be I'll grab a couple of your modules.

@localroger, thanks that info makes it worth a shot. Perhaps once the prop has used up the available higher voltage juice I can use the remainder to smoke a resistor, mission impossible style.

tubular

edit: @FearTurtles, you're right, 2.7 volts. Not a lot of margin for dips down that low, but then again I'm not switching any significant load

Post Edited (Tubular) : 6/3/2009 3:14:01 AM GMT

heater

After getting the voltage boosted a bit the question might be how long will it run from such a power source? You might want to be careful that your application spends most of it's time with all COGs stopped or waiting on something (waitpe etc). Any estimates.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
For me, the past is not over yet.

mctrivia

1000mah/10mah=100 hours

Estimate using 27mm battery

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
propmod_us and propmod_1x1 are now in stock. Only $30. PCB available for $5

Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.

Tubular

Heater, you're absolutely right. It will have the ability to run off external source (5v usb / 9v battery), but it also needs to be able to do some slow event handling. I'm confident that part of it I can keep well below 2mA.

I'll do some run-down tests and post the results running various applications...

tubular

Toby Seckshund

The A/Hr of cell is another of those perfect asparation figures, you will never get all that energy out to to useful work. The lower the draw over the longer period will get closer but any short sharp periods will degrade that which is available. Makers also count every last drop including that which is in "the long tail" the bit that is the end of its life. The cut off voltage of the project may not allow those last sips ti be got at. Buck/boosting allows a better useage of any energy until it has to let go but at a penalty of adding its own power requirements.

I wish that the prop had been designed for Li-ion voltage spreads of 4.2 - 3.7 Volts. This would allow battery useage without all the regulators with their evils.

hinv

Toby,

With the overdesign that has gone into the prop, I wouldn't be surprised if it worked just fine at 4.2 volts, but try it out at your own risk ;^)
On the otherhand, if it was designed to accept a wider range of operating voltages, wouldn't it just have a buck/boost built in, and therefore just loose the efficiency all of the time.

McTrivia: Isn't the buck/boost regulator in the 90% range of efficiency?

mctrivia

Up to 96% efficient. The inductor used accepts the entire voltage range of 1.8v to 5.5v but by using a smaller value that does not work for the entire range it can be made more efficient.

focus.ti.com/lit/ds/symlink/tps63001.pdf

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
propmod_us and propmod_1x1 are now in stock. Only $30. PCB available for $5

Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.

Toby Seckshund

Now that the price has fallen here in the UK, I am very tempted to risk "Old Backwards" to some more torment

The trouble is that a lot of the stuff I want to use batteries for are sig generators which need to give known levels, so a regulator is still needed. It just grates with me to use two Li cels giving 8.4 volts to only blow it down to 3.3 V, even if the cells are 2 AH and free. I suposse I should just accept it, after all 5 Volt batteries were a bit rare too.

Tubular

Toby,

There are some very low dropout regs, about 0.2 volts under load, which will happily regulate a 3.7v LiPo. Check out the LP3874 for instance. I'm sure there are others

tubular

Toby Seckshund

Ok I'll take a look at that one.

Many of the LDO regs I have been tempted by in the past do give regulation but their own quiecent current shoots up at that point. With 2AH cells I suppose it wouldnt matter too much but then I get all pious about energy usage and want it to run for lots of hours without recharges.

I should stop thinking of everything, and do something