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Pi 3: 1 hour @ 100% CPU!
11/17/2016 at 00:28 • 0 commentsSo previously I had tested that the LiFePO4wered/Pi with #LiFePO4wered/18650 charge board could be used with a Pi 3 with 4 cores at 100% in UPS mode. What I hadn't tested was how long it would last just running from a battery. I decided that this test was only relevant when run with production LiFePO4 cells. They arrived yesterday:
So I ran this test today. Unfortunately, I don't have access to the thermal camera right now, but I can tell you this Pi is HOT! :)
The results are in: 1 hour of run time with the Pi 3 at 100% CPU on all 4 cores and an active Ethernet connection! Very happy with this result. :)
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Improvements coming :-)
11/10/2016 at 17:14 • 0 commentsAs I've talked to more customers, two wishes keep popping up:
- Customers want to use the LiFePO4wered/Pi as a UPS for the Pi 3.
- Customers want to know whether USB power is present, and have an option to auto boot when it is.
So, work has started to make both of these wishes a reality. :)
For the first request, the limiting factor in making the LiFePO4wered/Pi work well as a Pi 3 UPS is not the LiFePO4wered/Pi power manager itself--it is perfectly capable of powering a heavily loaded Pi 3. The problem is the limited charge current of the #LiFePO4wered/USB charger. It is limited to ~500 mA because of limitations of the AA LiFePO4 cell and the linear charge chip that produces a lot of heat. It works well for the power requirements of the original Raspberry Pi, but not for the more recent, high powered versions.
To overcome these limitations, I have started a new project: #LiFePO4wered/18650. This is a drop-in replacement for the #LiFePO4wered/USB that is designed with a larger 18650 cell which allows higher charge currents, and a switch mode charger similar to the one I prototyped in the #LiFePO4wered/Solar1. This enables higher charge current without dissipating as much heat. I have running prototypes right now:
This project also includes features to solve the second issue: detection of VUSB. Where the center two pins of the 4-pin header connecting the LiFePO4wered/USB to the LiFePO4wered/Pi used to be the D+ and D- USB signals, D- on the #LiFePO4wered/18650 by default will have ~25% of VUSB connected to it (this can still be reverted back to D- for those who need it with a solder jumper).
But that's only part of the solution. The current LiFePO4wered/Pi power manager doesn't connect this signal to anything. So I had to make a change there as well. Since I was running low on LiFePO4wered/Pi panels anyway, I made a tiny change and added a trace to the LiFePO4wered/Pi to connect this pin to an ADC input of the microcontroller that was conveniently available before I ordered new panels. They have now arrived:
My CM is building some new stock for me and part of the new stock will be based on these panels, so they will be ready and available by the time I'm ready to build production of the #LiFePO4wered/18650. Since the hardware at that point will be capable of detecting VUSB, it will only take a little bit of software work to make VUSB detection available! :)
This brings up another issue. When I was first writing the LiFePO4wered/Pi software, my mind was very centered on the power manager by itself. So when naming the voltages, it made sense to name the incoming (battery) voltage VIN and the output (Raspberry Pi) voltage VOUT. I realize now that this is confusing to customers who deal with the complete unit: you'd expect VIN to be the USB input voltage instead. This will only get more confusing when I will actually have the USB voltage available as well. So I have decided to rename all current references to VIN to VBAT. I will update both the host software and the documentation to reflect this.
I realize this may cause some confusion with current customers, but it seems to be the best option going forward. The longer I wait to straighten this out, the worse the problem will get. Existing customers can keep their software as is and continue to use VIN, or they can update their software with:
git pull python build.py sudo ./INSTALL.sh
This gets the update from Github (network required), rebuilds and then reinstalls the software to get up-to-date with the new VBAT names. I hope this won't cause too much confusion, sorry if it does! -
New option: stackable header!
11/02/2016 at 18:59 • 0 commentsSome users wanted to be able to use the LiFePO4wered/Pi in combination with other HATs and GPIO mounted modules. Good news: I now offer the option to have a stackable 40-pin header on the LiFePO4wered/Pi to be able to do just that:
Here is an example of the LiFePO4wered/Pi used in combination with a HiFiBerry:
If you were looking to do something like this, head over to my Tindie store and grab one! Stock is going to be limited for now until I can gauge the interest in this option.
And please keep the comments coming! I love to learn from users what would make this product even better. :)
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New batteries!
10/31/2016 at 20:20 • 0 commentsSorry to everyone who was waiting for the little logistics hiccup, but I now have 500 new cells in stock! They are from the same supplier but slightly different from the old cells. Take a look:
As you can see, the old cell on the left has a "button top", the new cell on the right a "flat top". This works perfectly fine in the new battery holders, and it causes a less tight fit as well, alleviating any mechanical stress concerns that may have been left after the switch to the new battery holders. These cells fit very comfortably.
In the picture below, an old cell is in the unit in the front, a new cell in the unit in the back. The spring has slightly more room to expand.
The new cells also say they are 600 mAh instead of 550 mAh. I haven't done any testing yet to figure out if they really have more capacity or if that's just marketing. :)
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Oops, a bug!
10/12/2016 at 20:49 • 0 comments@Doug Wyman discovered a bug in the LiFePO4wered/Pi firmware. :-/ Better sooner rather than later, so thanks for the help Doug!
The MPS430G2231 micro I'm using on the LiFePO4wered/Pi integrates the very low level USI peripheral to support I2C. This is not a stand-alone I2C hardware peripheral, but mostly just a glorified shift register that requires a lot of software support to behave correctly as an I2C device. Unfortunately I screwed something up in the supporting software, and wouldn't correctly release the SDA line on NACK or when the device address didn't match. The result was that the LiFePO4wered/Pi would trash the bus when the Raspberry Pi tried to talk to another I2C device.
If the LiFePO4wered/Pi is the only thing you connect to the Raspberry Pi I2C bus, this bug will not cause you any problem. It will only show up if your Raspberry Pi communicates with another I2C device in addition to the LiFePO4wered/Pi.
If you run into this problem, get in touch so we can figure out how to fix it for you. Any new LiFePO4wered/Pi's bought from now on will have this bug fixed!
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LiFePO4wered/Pi RELEASE
09/01/2016 at 17:10 • 0 commentsRelease day is September 1, 2016, AKA today! :)
I'm going to style the release after a Kickstarter campaign, with early bird specials.
- Today at noon Mountain Time, I will be putting up 10 units at the "Super Early Bird" price of $28 each. If they sell out really fast, I may add some more later in the day.
- Tomorrow, 10 more units at $29 each
- And so on...
If you have been following this project, you're the first to know, so make sure you get them while they're cheap! Here's the link again:
https://www.tindie.com/products/xorbit/lifepo4weredpi/
Again, thanks for the support to all my followers!
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Better battery holder!
08/31/2016 at 22:58 • 0 commentsI've had some comments from pre-release customers and #LiFePO4wered/USB customers about the poor fit of the LiFePO4 cell in the battery holders. The LiFePO4 cell is a millimeter or so bigger than a standard AA cell and caused the battery holder to warp.
I'm glad to announce that I have qualified a different battery holder, which provides a better fit for the LiFePO4 cell. It's still snug, but the plastic hardly warps and there is extra plastic holding the battery in the holder very securely. In the picture below, the new holder is in front and the old one in the back:
All pre-release customers will from now on be receiving units with the new holder. The remaining units with the old holders (which work just fine as well, but look a little less good) will be shipped to customers of the early-bird release sale. :)
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LEDs without an LED in them?
08/29/2016 at 22:51 • 0 commentsOk, here's an odd problem I hadn't expected: up to now I have found 2 LiFePO4wered/Pi units with a defective LED. I just replaced the first one without investigating it thoroughly, but when it happened again, I decided to take a closer look at the problem. Below is a microscope picture of a good LED:
You can see the LED die and if you look closely, even the bond wire. Now, take a look at the picture of the defective LED:
I'm not sure what happened here but there's just no LED die in this LED package! That's the craziest thing ever. How can Lite-On get away with that? I thought they were a reputable manufacturer. I bought a full reel of Lite-On LTST-C190KGKT from Digi-Key, so you'd expect them to be genuine. Anyone ever seen something like this?
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Production PCB thermal performance
08/29/2016 at 15:41 • 0 commentsI had mentioned before (when talking about the thermally improved layout) that in addition to the improved layout, I'd make the production #LiFePO4wered/USB base boards with 2 oz copper, and that this hopefully would improve thermal performance even more. So meanwhile I have been able to run some tests on production boards, and it sure does:
The graphs show the battery voltage when charging from empty loaded with a Pi 3, connected by Ethernet and with an SSH connection for logging. As you can see, the 2 oz copper presents a significant improvement.
It also looks like the heat sink doesn't make very much of a difference. Because of this, I'm going to provide the heat sink as an option instead of building every #LiFePO4wered/Pi with a heat sink attached. All the pre-release units will continue to be shipped with this option though.
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Pre-Release!
08/25/2016 at 16:18 • 0 commentsYou can now BUY the #LiFePO4wered/Pi! :)
I'm calling it pre-release. You pay more than the eventual price, but you can get it before everyone else, and you are entitled to personal support if you need it.
I'm mostly doing it as a way to ramp up my production process slowly and to get feedback from early adopters in case something isn't right or documentation needs to be improved. Also, it provides a way for people or business to sponsor my development if they like what I'm doing. I very much encourage it. :)
I already got my first order of 2 pieces before I even got a chance to announce the pre-release! Thanks Jeff, your LiFePO4wered/Pi's are ready to ship!
So if you want one, head over to Tindie!