battery powered prop device

smbaker

I'm considering a project that would use a prop, most likely powered by a 9v battery. Let's assume a goal of 30 hours of operation before the useful life of the battery is depleted. Let's assume a battery rating of approximately 600 mAh (according to google, typical for an energizer 9v).

In addition to the prop, I'm going to have to illuminate a LED, let's assume that a superbright LED powered down to 1ma will be bright enough. I'm also going to have to talk to an SPI device or two, but they're only rated in the tens of microamps.

I realize this is an oversimplification, let's say we can pull 20ma for 30 hours = 600 mAh. 1ma of that will go to the LED, 1ma slop factor for everything else, leaving 18ma for the prop, eeprom, and the voltage regulator. Is it a realistic goal to operate a prop and a 3.3v regulator at this limit? I'm assuming we could power down as many as half the cogs, and reduce the frequency to reduce power consumption. A prop is overkill for my application, but... I understand props, and when all you have is a hammer, everything looks like a nail.

Assuming this is doable, what type of regulator would be most appropriate?

How about pushing it one step further an operating off of a lithium coin cell battery, let's say 3V at 180mAh (can this be done with no regulator?). That would lower the requirement for the prop down to around 4ma.

Leon

I'd use something else if you want a regulated supply, a PP3 battery is a very poor choice.

I've used PICs with two AA cells as an unregulated supply, as well as a Li coin cell. It's the way to get maximum battery life.

Another choice is a single cell (1.5V) with a boost converter delivering a regulated supply. That is getting popular, as the cell can be run down to under 1V.

smbaker

Hmmm, now that I think about it, two AAA would probably be a better form factor than a 9V anyhow, and would make a lot more sense. Just means having to fab up some battery holding tabs on the PCB. The only thing better for my app would be a CR2032 (or even better yet, a CR2450 -- 3.0V at 625 mAh).

Sounds like it's time to do some experimenting.

Mark_T

Lithium coin cells aren't good for many milliamps, very high internal resistance - using the slow RC clock would be fine of course!

jazzed

smbaker wrote: »

Hmmm, now that I think about it, two AAA would probably be a better form factor than a 9V anyhow, and would make a lot more sense. Just means having to fab up some battery holding tabs on the PCB. The only thing better for my app would be a CR2032 (or even better yet, a CR2450 -- 3.0V at 625 mAh).

Sounds like it's time to do some experimenting.

I have some DIP32 modules for sale that use a boost converter for low voltage operation at 1.3 to 4.0 VDC. They will run on a single AA Alkaline cell, but 2AA Alkaline or NiMh will last longer.

The attachments show 6 modules on a panel and a rendering of the development board. Modules are $50 each and the platform board will be available soon. Module connectors are suitable for bread-boarding and low profile stacking. PM me if you're interested.

--Steve

Tracy Allen

If you need a low quiescent current linear regulator, ones like the MCP1702 from Microchip operate with mere microamps of quiescent current with either light of heavy loads, due to their pmosfet output driver.

A lot may depend on whether or not your project can take naps between rushes of activity. The prop on RCslow can operate on a few microamps, then wake up to RCfast or to xtal power only when needed. A capacitor across a lithium coin cell can provide current for bursts, how much is a quantitative question.

A pair of AAA cells are okay, but alkaline cells do fall off in voltage with age. Lithium Iron diSulfide primary AAA cells have about 1200 mAh capacity, and maintain pretty much a constant voltage thru their life.

evanh

Highly recommend the newer low-self-discharge NiMH. They make alkalines obsolete. The original Sanyo Eneloop has the longest self-discharge curve but there are others like the Yuasa Enitime that have significantly larger capacity.

Use the single use lithiums if you are looking for 5+ years on a single use. Otherwise the new NiMHs rule, plus you get to recharge them instead of throwing out.

jeff-o

Don't use a lithium coin cell. The bigger ones may have a capacitor of 600mAh, but that's at an extremely low discharge current. If you're running a propeller and other stuff it will discharge very quickly. I know from experience - my Prop-based Plant Whisperer board was originally designed to use a lithium cell, but I scrapped that plan after it died after only a few hours. I switched to AA batteries and it worked fine after that.

WBA Consulting

Not sure about specifics since I didn't track things exactly, but my Plungelogger runs from a 9 volt battery through one of my PowerTwigs and I had it running for a pretty long time without killing the battery. The Propmodule 1x1 is no longer available, but the circuit was a basic propeller circuit.

If you are looking for a small, ready to go solution, Jazzed's DIP32 modules are probably your best bet. My M44D40+ module is a small Propeller platform in a DIP40 form factor, but does not have any power circuitry on board. Link for that is in my sig.