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?

One more thing worth mentioning: This guy has, I think, a correct insight into why auto-leveling may not work as well in the real world as it theoretically should:

Blank PCB material is not as rigid as it appears, depending on its size and how it was stored (not to mention how you mount it) there will be some bowing which results in a curved surface under your engraver.

Unfortunately, the probing process doesn't put enough pressure on the board to push it down while the actual engraving process will. This means you will get shallow cuts even with an autolevelling process.

The trick is to ensure that the probe pushes the board down to it's fully flat level before measuring the height at that point. My solution was to put a small ball on the spindle that is 2mm lower than the probe tip - as the probe moves downwards the ball pushes the PCB to the underlying bed and compresses before the probe makes contact. This gives you a far more accurate depth reading.
https://blog.thegaragelab.com/seven-pcb-milling-tips/

His solution looks like this:

which looks as though it could be improved upon.

Hi Andrew!

Great to hear from you and your updates.

@andrew said in CNC PCB milling:

I'm curious whether you can use smaller ones to deal with the 6mil/6mil trace/isolation sizes.

Yes, I'm wondering the same thing. There's reason to be hopeful that it can be done: I've seen a number of 0.1mm end mills for sale, and that's roughly the the bit diameter that would be needed. After I upgrade my stepper motors to higher torque models, and after I upgrade them even further to be closed loop, I'd like to give it a try. Fine pitched etchings like that would probably also greatly benefit if solder mask could be applied afterward, and so I'm hoping to learn how do that as well:

https://www.amazon.com/MECHANIC-Prevent-Corrosive-Soldering-Welding/dp/B076YPKBKL

Join the fun! With your new machine already on the way, you may be ready to give it a try before me.

When you get a chance, please do let us know how you like your new CNC. It looks a lot sturdier than the CNC that you will soon be selling.

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I ordered 3 of these closed loop mechaduino clone controllers that utilize 12-bit encoders:
https://www.aliexpress.com/item/32917408111.html?spm=a2g0s.9042311.0.0.44f74c4dxgjrOv

The uStepper hardware specs are better, at least on paper: 16-bit encoders and higher voltages, but at 4x the price, plus even more cash if you want an equivalent OLED add-on with buttons. For sure Ustepper's trinamic hardware is very tempting, but I'm not sure how solid the uStepper firmware currently is, whereas the mechaduino firmware has been tested for a few years now. I also get the impression, perhaps incorrectly, that the ustepper documentation is comparatively sparse right now. So, for all those reasons, I chose mechaduino over Ustepper. Maybe later, somewhere down the road, I'll give Ustepper a try.

ETA for the mechaduino's is about a month from now. I'll report back after I've received them and given them a try.

Meanwhile, on an unrelated topic, I was finally able to test one of the tiny diameter endmills:
https://www.amazon.com/gp/product/B06WRWLK79/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1
and Wow! It works great. My first impression is that this is the solution I've been looking for: just set the cutting depth to be "more than enough" and you can isolation cut all the traces in one pass while keeping the desired trace width. Much faster and easier to use than v-bits, IMHO.

Makerbase MKS SERVO42A NEMA17 closed loop stepper motor Driver CNC 3d printer parts prevents losing steps for Gen_L SGen_L

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For flattening the spoilboard, I ended up trying the 1/2" freund:
https://www.amazon.com/gp/product/B00004T7BL/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1
rather than the 1/4" freuend. No worries: it posed no challenge for my spindle motor.

The problem is that, unlike a fly cutter, this straight bit effectively cuts a kind of donut
around the central shaft, beause the blades do not extend inward enough. Even though moving the bit far enough will effectively erase the donut, I'm concerned it may create unnecessary resistance to downward plunging if the spindle is holding stationary in the XY plane. Therefore, the next bit I'm going to try is:
https://www.amazon.com/Cleaning-Diameter-Spoilboard-Surfacing-Proburs/dp/B07BF5ZHD1/ref=cm_cr_arp_d_product_top?ie=UTF8
which looks to be more like a fly cutter and, if so, should avoid creating pegs directly underneath the spinning shaft.

I'm also going to try:
https://smile.amazon.com/Spoilboard-Surfacing-Diameter-Flattening-NITOMAK/dp/B07ZP5RXRP/ref=sr_1_1?dchild=1&keywords=CNC+Spoilboard+Surfacing+Router+Bits%2C+1%2F4+inch+Shank+1+inch+Cutting+Diameter%2C+Slab+Flattening+Router+Bit+Planing+Bit+Wood+Planing+Bit+Dado+Planer+Bit+by+NITOMAK+(Carbide)&qid=1596707793&s=industrial&sr=1-1
simply because it is so highly rated for flattening a spoilboard, even though it is likely to produce some amount of pegging directly beneath a shaft that is not moving in the XY plane.

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I just now came across a dedicated autoleveling program that allows you to do a two-stage autoleveling. This has at least a couple of advantages over the much more common one-stage autolevelers that's typically encountered: 1. you only need to probe once. If your CNC job gets derailed, you don't have to re-probe, and 2. you have the opportunity to review and correct the probing values in case something went amiss during the probing. AFAIK, this program should be compatible with whatever g-code sender you may wish to use.

https://www.youtube.com/watch?v=ZbfS92Zvzz8

For instance, auto-leveling has been broken in the Universal G-Code Sender for over a year now. Perhaps this could fill the autolevelling need not currently being met by UGS.

[One thing I like about UGS is that it constantly updates its best guess as to the estimated time of job completion. Very handy! Seems like an obvious feature for a g-code sender to have, and yet many/most g-code senders that I've tried seem to lack it.]

@bikerMark At the beginning of this youtube the guy utilizes a laser to do very selective curing of a PCB's etching mask:

https://www.youtube.com/watch?v=So-6lgmVhA0

First time I've seen it actually done. I presume the very same approach might work for solder mask too?

In case anyone is interested, BigClive tried out some inexpensive gear that's at least notionally similar to what I described above for making Hypochlorous Acid:

https://www.youtube.com/watch?v=R5kcER2Z4-8

Judging from his teardown, it seems so ridiculously simple that it would be quite easy to DIY your own. I'm guessing that the only part that might differ in quality is the electrode. Presumably a platinum electrode (or maybe even just a platnum plated electrode?) would be the ideal choice, but BigClive speculates that maybe stainless steel might also work.

@bikerMark said in CNC PCB milling:

Time is no issue here; quality and reliability are. I use 30° piramyd bits, they are very well pointed and the machine has very little runout, so I realy need those five passes. I love these bits (eg https://tinyurl.com/yyg6hsft) : they're stable, sturdy, hardly breakable and when needed I can sharpen them myself.

Thanks for the tip! I just now ordered some.

I'm a bit unclear as to how you are using the laser, but it sounds interesting. Although different from what you are doing, I imagine that using a uv laser to selectively cure solder mask would be the ultimate. By not curing the solder mask over the pads, you could just wash the uncured soldermask off later. Would it work? I guess it depends on whether the uv laser can be focused well enough that it only exposes what you want it to.

How fine a pitch can you etch with your setup? That's the real test, especially given how finely pitched a lot of smd parts are.

It's now possible to use an inexpensive open source controller to achieve both closed loop control and 0.02 degree resolution on a nema 17 stepper: https://hackaday.io/project/11224-mechaduino

I get the impression the original maker isn't selling it anymore. So, you can make it yourself from the files posted or github, or a number of inexpensive clones are also available on aliexpress for around $15. By use of a magnetic encoder, it basically immediately corrects for any missed steps. In the case of 3D printing, that means no layer shifts, even if, as demonstrated in this youtube video, you were to whack the printhead hard with a rubber mallet during a print:

https://youtu.be/eM8zSG8fEkk

As for CNC, it's a new level of control assuredness.

Also, because the drivers offer a way to directly monitor how hard the servos are working, they should provide a way to make better informed decisions about increasing speed, acceleration, etc.

UStepper appears to be another board that was conceived along similar lines.

I'm planning to upgrade my nema 17's to ones with 3x the torque, and then later upgrade those upgrades with mechaduino/ustepper closed loop controllers. By sticking with nema 17, all these should be drop-in replacements for what's already there. i.e. no need to change couplers or other fittings.

For even greater torque and precision I could outfit the steppers with planetary gearboxes, but, meh, I'll evaluate that after the upgrades already pending are completed. I presume they come with a downside of much slower speed.

Anyone here done any of this? How did it go?

@niallain As far as v-bits go, I've lately had good results with this type:
https://www.amazon.com/gp/product/B019K4OMBE/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

It's not as fragile as the typical aliexpress style v-bits.

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