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!

@OldSurferDude If I have a question about something I generally post the question. Sometimes someone will answer it, and all is good. But on those occasions where no one answers it to my satisfaction, and I later do figure it out myself, then I return and post the answer to my own question. I think if everyone followed this protocol, it would help. What I see across forums (not just mysensors, but just about all forums everywhere) is people who post questions with a "Thanks in Advance" attitude, but who never bother to close the loop if they do find the answer. Or they never confirm whether or not someone's suggestion worked or didn't work. The result is that when searching for an answer, one has to search through a lot of posts which don't contain any useful answers. So, I would encourage everyone to return and post answers to their own questions, if no one else already has, because in all likelihood someone else will have the same question in the future. I think that one small change might make a huge difference.

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.

For sure, the store shelves are pretty much overflowing with smart home products and IoT these days, much more than in the past. Is it just diffusion of attention, or do people just buy what they need now in complete systems or something? Or buy stuff that has phone apps instead of a hub? Or has Home Assistant taken over? Or Amazon Alexa? Not much in the way of new postings compared to the past. If anything, I thought there'd be more activity due to more and more IoT interest generally. If anything, it seems like Mysensors has a more robust and complete system now than in years past, and it's broad enough to include just about everything. What gives? Have off the shelf prices dropped so far that the economics no longer favor rolling-your-own or something? i.e. buy rather than build? Where's the new frontier? Is it now AI and system level stuff? I'm really curious. I mean, not all that long ago Google bought a thermostat company (Nest) for over a billion dollars. There's clearly been a sea change, and I'm just wondering what changed.

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.

@alphaHotel The 17.75mm separation is as close as they can get and still use an M3 on the mounting holes. For the 16.75mm boards I have on order, I reduced the mounting holes to M2 sizing.

The long turnaround time when ordering PCB's is a frustration. I should get my cheap CNC PCB etching machine up and working again to resolve these silly dimensioning issues without having to send off to a fab somewhere.

@alphaHotel said in Most reliable "best" radio:

It's looking good! I'm curious, how far apart are the battery clips now (center-center)?

Most likely it will be either 16.75mm or 17.75mm. 17.75mm is plenty wide. I have some test boards coming at 16.75mm to see if losing 1mm still guarantees adequate separation.

As for which USB connector, it depends on context. If size is not an issue, then lately I'm liking USB-B more than USB-mini. It's the same USB connector commonly found on the classic Arduino Uno. Super robust. I recently sourced 10 of them from mouser: https://www.mouser.com/ProductDetail/490-UJ2-BH-2-TH at close to 50 cents each.

Here's the first pass on the new version:

The good news:

• I widened the separation between the batteries, and now the clips aren't at risk of shorting against one another.

• list itemThe machine pins now sit nice and low against the PCB. The idea is that this way a shield can arch overhead without having to add much to the overall height. That's why I have regular headers on the outside part.

Not so great: as a guard against shorting against the clips, I maybe overcompensated by overwidening the headers as well. I think I can probably narrow the overall board width by 3 to 6mm and still have adequate clearance. I'll do some more iterations until I zero in.

Also, unlike the earlier test platform, this board lacks a way to separate out current measurement to the radio vs to the mcu. Since I already have the test platform for that, I don't think I care, but maybe someone else would want that? It could be added to the backplane, or it could be added to the plug-in modules themselves.

Lastly, I'm noticing that the battery clips fit so tightly against the PCB holes that you probably don't even need to solder them!

@alphaHotel said in Most reliable "best" radio:

@NeverDie said in Most reliable "best" radio:

@alphaHotel said in Most reliable "best" radio:

@NeverDie With the first version of the battery/MCU board, you lamented running traces directly under the batteries. You have the space now to re-route them but choose not to. Did you find a way to resolve the issue it caused?

Actually, I fixed it on the new version (pictured above). The red traces run on top, so they're adequately isolated from the battery holder metal, which is on the back side except for the through-holes where it sticks through the board. Where I ran into trouble was running traces on the back side, beneath the battery holder metal. If the battery holder metal was pressed up hard against the board, some shorts resulted on some of the boards. The workaround was to not press the battery holder metal hard up against the board, but the new version removes that concern entirely.

Okay, I see now. I misunderstood the original issue and also didn't think about the top/bottom side orientation in relation to those traces vis-a-vis the battery holders. Thanks for clarifying.

I received the PCB today, and I think I see now the source of your confusion: I had put the silkscreen outline for the battery and its clips on the FRONT instead of on the BACK where it belongs. I'll correct it on the next iteration. On this first iteration I'm mainly just testing for fit and to make sure the space is such that the battery clips don't short against either themselves or against the headers. I'll also be adding polarity markers as a reminder for the correct way to insert the batteries.

@ben999 said in nrf24+ module with stick antenna:

Please note that i do not need any additional range.

Please don't take this the wrong way, but have you ever heard the phrase "If it's not broken.... "?

That being said, if you want to do it anyway... you'll want to consider impedance matching and probably want a VNA to check your work. i.e. it immediately gets very complicated. If none of that matters, then I guess how you execute it doesn't really matter either: there's just GND and ANTENNA to wire up. GND goes to the outside, and ANT goes in the center. If it's not a dipole antenna, then maybe only just the ANT connection will matter. Just be aware that you might be worse off than before you began.

If, on the other hand, you wanted to add a wire-whip antenna instead, then you could theoretically start-off long and then trim the length down to tune it better.

I wish there were an easier way, but, AFAIK, almost nothing about antennas is straightforward if you want to do it better than what you already have.

I never realized you can send/receive BLE data using an nRF24L01:
use NRF as a BLE Module | Arduino NRF24L01 Bluetooth Low Energy Tutorial – 12:17
— electronic GURU

Unrelated to that,I found a nice introductory tutorial series on then nRF52:
https://www.youtube.com/c/SumairsEmbeddedEngineering/videos

Most of the nRF52 stuff on youtube only considers either just the hardware or just the bluetooth aspects, but this series covers much more than just that. Lately Nordic's development has embraced the Zephyr RTOS, but this youtube series does not rely on Zephyr, which may (?) be good if you want tight control over the hardware without the overhead of an RTOS.

I've had success getting the nRF24L01 to listen once per second for packets at an average current drain for just the nRF24L01 of 5.35ua. Not bad! The snag I'm running into though is that the listen window, encompassing power-up of the nRF24L01 through Rx mode is 1.6ms. However, if I use the atmega328p to time that 1.6ms, it raises the average current drain to 45ua, which is worse than my keyfinder keyfob's current drain (about 30ua on average). So....I need to find some way to sleep the atmega328p for 1.6ms in order to keep the total current drain low. However, how to do that? The TPL5111 has a minimum period of 100ms, so that's out. The atmega328p's WDT has a minimum period of 16ms, so that's out too. Unfortunately, the atmega328p has no built-in RTC. Even if I were to add an external RTC, I don't know of any that would let me dial-in 1.6ms.

Presently I can think of only two solutions:

1. Add some kind of external oscillator and feed it to Timer2 in asymchronous timer mode while sleeping the atmega328p. However, I can't seem to find from the datasheet what the current drain of that configuration would be, so it seems like a shot in the dark.

2. or, possibly use a GPIO pin to charge up an external capacitor and somehow calibrate the charging time so that when the capacitor discharges via some RC time constant it triggers a falling edge interrupt on the atmega328p to wake it up from sleeping after 1.6ms (the sleep time begins after it charges the capacitor). I haven't tried this, but it might actually work. It would notionally be kinda/sorta similar to how one can use an atmega328p to charge up a capacitor in order to determine the capacitor's capacitance value: https://www.norwegiancreations.com/2019/08/using-a-simple-arduino-to-measure-capacitor-value/.

If anyone has any other ideas on how to sleep an atmega328p for 1.6ms, please do post.

[Edit: Regarding #1, I suppose I could try measuring the sleep current with external asynchronous mode engaged but nothing connected to it. If it's acceptably low, I could then hook up an ultra low current 32.768K external crystal at an additional 500na or so. Hopefully there's some way tot turn everything off on the atmega328p except for the asynchronous counter. I'm doubtful as to whether I can apply such fine grained control like that to one of the sleep states (POWER_SAVE MODE), but maybe....? Here's some reason to be hopeful:

Power-save: is similar to the power-down mode, but the Timer2 is still awake and could be operated via an external clock.
https://wolles-elektronikkiste.de/en/sleep-modes-and-power-management

Ugh. Except Timer2 is an 8 bit counter...., but that's OK: 1.6ms would be 53 ticks on a 32.768k oscillator, so at least that part should work if the mcu sets timer2 to overflow in 53 ticks and then go to sleep and if that overflow will trigger an interrupt to subsequently wake the mcu back up after 1.6ms.

Well, it's a plausible theory. Just need to test it!

Is it worth the effort though? Even if it worked, an nRF52 module would outperform this type of setup, would be more compact, would be easier/faster to assemble, and would (probably) be lower cost as well. Hmmmmm..... And the nRF53 will be even better hardware still, though the nRF53 does come with the extra overhead of an RTOS....]

@NeverDie said in Most reliable "best" radio:

@alphaHotel said in Most reliable "best" radio:

E01-2G4M27D

I'm fairly certain the ones I ordered won't be arriving with antennas (as none were pictured in the aliexpress posting), but, no problem, I'll let you know for sure after they arrive. Most likely if you have an old wi-fi router that you no longer use, you could probably unscrew those antennas and use them, since they'd also be 2.4Ghz.

@alphaHotel Reporting back: I received them, and mine did not come with any antennas.

@Larson I haven't studied Kevin's solution, so maybe I'm missing the point of it, but the adafruit TPL5110 BoB is so much less expensive and draws so little current that it seems like no contest to me.

@Larson said in Most reliable "best" radio:

@NeverDie said in Most reliable "best" radio:

CORRECTION: Earlier I said that Adafruit's TPL5110 breakout board appeared to use a 1M pulldown resistor on DONE. I remeasured today and that's wrong. It's actually a 10K resistor.

Thanks for redirecting me to this thread. I think you were right on your original 1M Ohm assertion. Since I'm playing with my new TPL5110,s I took it on to make my own MM measurements. While my Harbor Freight MM might not be the most accurate instrument, I did show the resistance between DONE and GND to be 900 K'ish. Next, I got out the magnifying glass to spy the resistor in-line with said pins to have a marking of 1004. Google affirmed that that means 1 M ohm. So, your 5K, or 10K would be a big change – and if it comes at no cost for the quiescent current AND enables ESP action, then perfect!

I just now checked the adafruit schematic for the TPL5110, and you're right: it does show a 1 megaohm resistor. I guess I must have measured it wrong. https://github.com/adafruit/Adafruit-TPL5110-Power-Timer-Breakout-PCB