Not sure if others would have interest in this, but I'm designing a PCB for an easy-to-solder TH node. As presently conceived, it would have 3 surface mount components (an LED on the front and a resistor and capacitor on the back), plus a DIP atmega328p, a header to accept an inexpensive si7021 TH breakout board, an FTDI header, and an RFM69HW. The idea is that it would run at 8Mhz and be powered by two AA batteries, so it's sized to be compact but still easy to solder. The same thing could be achieved with wires and some of the other boards out there, but this might be a little tidier if a TH mote is what you want as either the starting point or the end-point.

PCB dimensions are 0.65x2.55 inches. i.e. it is narrower than a typical AA battery holder, but roughly the same length.

The LED and resistor are optional, and you could forego the capacitor as well if you wanted a truly bare bones TH solution. However, the pads are there if you wanted to utilize them. Also, you could skip the si7021 BoB if you wanted just a generic mote.

I had hoped that someone would make an easy to solder board like this for the RFM69HW, but I got tired of waiting and finally decided to just make my own.

I found a good place to do range testing.... too bad I didn't bring the gear!

Good news! Last night I did some accelerated load testing on the supercap. First I charged it to 3.6v and then I hooked up an RFM69HW mote which woke up once a second to do 3 things: 1. check the voltage level, 2. turn on an LED for 1ms to simulate a sensor load, and 3. transmit a packet containing the voltage data using the RFM69HW.. Bottom line: 14,111 packets transmitted before running out of juice.

Not bad for a first attempt.

Yesterday received the PCB. Today assembled for testing this battery-powered nRF52-based passive infrared motion detector:

Made this 12 button keypad. Requires only one analog pin to read which button is pressed, and any button press can also wake an arduino from sleep:

Consumes no power when no button is pressed.

A pair of lithium AA primaries is hard to beat because:

1. Unlike alkaline's, they don't leak.
2. Have a look at the discharge curve: https://data.energizer.com/pdfs/l91.pdf By the time they drop to 2.4v, if not before, you'll want to replace them.
3. Obviously much longer life, both shelf life (20 years!) and energy capacity.

I think running 8Mhz from the internal RC is a no-brainer: wake up time is less than 4us. So, if your node wakes up often, you'll save a ton of energy over time.

The best time to take your battery measurement is immediately after a Tx. That will give you the most conservative reading. Save that measurement in a variable and then send it in your next transmission. Switch on your ADC just before Tx and take your first ADC measurement during Tx, because you have to throw out the first measurement anyway. That way you can take a fresh (and valid) ADC measurement just after Tx before the voltage rebounds.

Hope that helps!

Here's the version that I most recently assembled:

As you can see, the 15F supercap is now on the board itself. It works fine.

I've since made a few refinements and have sent the new files off to be fabbed. The newest version of the PCB will measure roughly 22mm x 22mm.

Put together this pro mini nRF24 shield for testing...

I have a number of sensor projects that sit within the nice footprint of a Pro Mini. Now I want to find a kind of universal power platform--hopefully small--to power them. So far, what I came up with was this, which runs the Pro Mini from 2xAAA batteries, and where the Pro Mini (and whatever the project built on it) simply "plugs in" to it:

Is there anything better? Ideas? Comments?

@TheoL said in Best 3d printers:

But I can not see what the big differences are. Would it be possible to add auto leveling later on?

Yes. Autoleveling can be added later. I have it on both my Prusa I3 MK3S and my Ender 5 Plus, which came with it stock. The bigger the build area, the more useful it is. My creality doesn't hold its manual bed-leveling all that well (a common complaint among Creality owners), so the auto-leveling really helps a lot. The Prusa I3 MK3/3S is considered a well tuned and reliable printer. My Ender 5 Plus, after a lot of
upgrades, prints almost as well, but from what I've seen Creality's engineering just isn't as good, and upgrades are needed to bring them to a more polished Prusa level. In my view Prusa's are a printer and Creality's are a project. By that I mean Prusa's work well in their stock configuration, whereas with Creality printers you'll probably want/need upgrades. I got the Ender 5 Plus because I'm in the middle of a project where I'm printing not just bigger things than the Prusa I3 MK3S can handle but also because I'm printing a lot of them, and the bigger build surface allows me to do it in parallel.

I think people here are right when they say you'll eventually want a bigger build area, but I started with the same goals as you and for me it took 2 years before I felt I needed the bigger build space (and then only because my goals are now different). I don't really regret buying the Prusa with its smaller build volume first, however: over the last two years prices on bigger build-volume printers has fallen by a lot and quality has increased by a lot. I expect those trendlines will continue. Also, I could probably sell my Prusa today for more than I paid for it two years ago, because it's already built and there's a market on ebay of people who don't want to assemble a kit and who dont' want to wait one or two months for a shipment from Czechoslovakia. In fact, when my current project is finished, there's a good chance I will sell it on ebay while it still commands premium pricing. The Prusa was cutting edge for its day, but the other printer companies are catching up and you can now buy 3 of them for the price of one Prusa.

If I hadn't been in a rush, I probably would have purchased an SK-GO instead of an Ender 5 Plus. That said, an SK-GO is not intended to be anyone's first printer. The Jubilee 3D printer also looks very promising, as it supports automatic changing of printheads (something that usually only multi-thousand dollar 3D printers can do), which is the next big trend. Another kit worth considering is the Voron 2.4, which is a fully open source alternative, but again, as a first printer it would likely be overwhelming for most people.

For comic relief, consider:
Voron life - a film, by Madcat – 04:00
— Andrew K

@Theol I had thought you were in the USA when I recommended amazon or ebay. Not sure what consumer rights buyers in Europe have, so I have no advice on where to buy there.

@TheoL What size build volume do you need?

If you have no idea what you should want/need but you just want to get your feet, then I'd say the Ender 3 is a reasonable starting point for learning purposes. I would have said Ender 3 Pro or Ender 3 v2, but from what I've read, many if not most if not all of the Creality silent stepper designs are incapable of doing linear advance, which in my view puts a limit on their usefulness. The Prusa mini might be a good choice if you're OK with its smaller build size.

I'd strongly recommend buying from Amazon or Ebay if you can, because both have reasonable return policies. I've read a lot of horror stories about people receiving bad Asian 3D printers purchased through other sources and being stuck with it and unable to get their money back. In fact, I get the impression that the primary business model for much of the Asian 3D printer market is to over promise and under deliver, sometimes dramatically so.

@martim said in RF Nano = Nano + NRF24, for just $3,50 on Aliexpress:

@TheoL way to expensive.

For less money, and very little effort, you can put your own together: https://www.openhardware.io/view/480/Compact-nRF24L01-Pro-Mini-Bottom-Shield

As demonstrated, it also gives you more choice and control over the type/quality of nRF24 module that you get.

@ncollins said in What did you build today (Pictures) ?:

10P 0.5 FPC connector for programming and serial debugging

How many of the 10 pins do you actually use?

When are you measuring the battery voltage? Before or after a transmission? My guess is before. The better measurement is if you measure immediately after transmission, before battery recovery, and then save the value for reporting during the next subsequent transmission. That's especially true for coincells, whose voltage tends to droop a lot after pulling a current.

@monte said in nRF5 action!:

I hope others will appreciate it too.

Yes! Any examples which shed light on how to write a custom bootloader for the nRF52 would be greatly appreciated.

@willemx

Remembering now, the undervoltage and overvoltage protection could both be put under the MCU's control, in which case you could get by with just a diode, or equivalent. It wouldn't be as failsafe in the sense that an unforeseen bug in your code might defeat it, but it could be done. In the end, I'm not sure that the chance of encountering a failure in software is necessarily any higher than that of encountering a failure due to defective hardware.

Alternatively, you could put two cells in series, and in principle that would eliminate any chance of overcharging. With that configuration, if you used a 5v solar panel instead of a 6v, then you'd also eliminate any chance of burning out the atmega328p and wouldn't need extra hardware to ensure against that.

For that matter, you could stick with one cell and just use a 3.5v solar panel. With just that one stroke you wouldn't need anything extra to guard against overcharging the battery or over-volting the atmega328p.

That's what makes embedding solar such a fun problem--depending on the use case, there are such a large number of different ways to solve it. So many that the real game is in comparing the trade-offs.

Nice. Will your solution be open source or closed source?

I like that your solution includes wifi. There are similar sounding bluetooth-only solutions on the market, but then range can be an issue when it comes to automated monitoring.

There are also some OBD solutions out there. Not sure if they measure the voltage directly or instead just query the car, which maybe does it own measurements. I recently purchased a BlueDriver for the purpose of checking OBD codes. There are many, many products to choose from (what seems like hundreds) , making it very hard to determine which ones are the best. At the same time, perhaps 80-90% of them, based on reviews, are so poorly implemented that they're nearly rubbish.

@SuperNinja May not work on the OP's LifeP04, so I guess it depends on whether the OP wants to stick with a LifeP04 or change battery chemistry.

@willemx said in Need advice on solar powering with LiFePo4 battery:

my nodes only send a few dozen messages per day and are in deep sleep 99.9% of the time, so I do not need much power. I don't expect battery temperature to be an issue in my setup (I live in the Netherlands, very moderate climate)

Those requirements could be met quite simply with an LDO, diode, and a supercap. For a cheap (but not the best) solution, you could consider just an LDO for charge termination plus a diode on your Lifep04. It would not guard against overdischarge though. A supercap doesn't need to worry about overdischarge.

I just now looked at a lifep04 battery on amazon.com with built in high and low voltage cut-off, but the low cutoff was so low (2v) that I wouldn't recommend it. Nonetheless, the entire thing (battery with built-in protection) costs only around $1.80, pro rata.

I don't see that the TP5000 has an undervoltage cutoff.... Not sure if it does or not. Depending on what kind of longevity/cycle-life you need to guarantee, you may or may not care about that.