CurrentRanger review & availability

Sunday morning I woke to an unusual amount of email asking about the CurrentRanger availability. And the limited stock was all gone, so I knew something happened.

I was then pointed to to Andreas Spiess’s latest video:

Thanks to Andreas for posting a thorough review of the CurrentRanger, I especially appreciate how he was able to quickly tune the code to his own needs and customized the CurrentRanger to behave the way he wanted.

He also kindly posted a 3D printable model of the case he shows in the video, some folks already printed it and it looks great! Find it on thingiverse here. The stock case needs some modification to fit the green terminal and access to the USB case, as well as allow mounting the buzzer. If you have a 3D printer you can print this case and keep the black stock case for another project, thanks Andreas!


I am working to get more units in stock this week. There are a lot of moving parts to making this product. First a large BOM and a complex assembly and testing procedure. I want to ensure to the best of my ability that each unit is able to deliver what it claims.

Some components like the banana jack terminals and OLEDs come from the place we hate to love, China. I’m currently waiting for the small banana jack terminals and OLEDs. However I have a surplus of GOLD terminals, and could replace the small terminals with those if some folks are interested – let me know!


I can understand concerns about the cost especially for hobbyists or students. Let me reiterate what I’ve already mentioned in the forum and to others. Here’s the TL;DR of that:

I always tend to design something that I would first and foremost use.¬†While not a high end product, this is not a toy either. I spent over a year – among other things of course ūüôā – developing this product and I put a lot of thought into pricing it before release. I’m not interested in selling high volumes at razor thin returns on my investment and my effort. I prefer fewer sales for people that can appreciate it and not abuse it. I think it was priced fairly, given the high cost of the BOM and the complexity and time it takes to make and test, it really is probably the most complex thing I ever made both in hardware and software. Also, it is not much more expensive than the uCurrent, I am sure anyone reasonable who understands the differences and the set of extra features (perhaps watched the video above for some contrasts), can appreciate all that for just $30 more. The uCurrent is always a great option for those needing accurate current measurements at a lower price.

Romania: Happy 100th birthday!

My readers may not know that I hold dual citizenship, and was born and spent my first 19 years of life in¬†Oradea¬†– a beautiful city at the foot of the pittoresque¬†Carpathian Apuseni mountains and in the western part of Transylvania – the legendary land of Dracula’s castle.

Today’s blog is not about electronics or making stuff, but about what in great part shaped me and perhaps dear reader – what made some things great and significant for you as well. Maybe you’re not a history enthusiast, but maybe you’re a woman engineer, or perhaps you stepped foot in an airplane that took off on its own, used a fountain pen, or depend on insulin, or maybe you just own a LowPowerLab product that has bettered your life in some way – you might be surprised to find out which nation gave the world their inventors.

What’s the big deal?

Today – December 1st 2018 – marks a special anniversary for me as a Romanian diasporan. Exactly 100 years ago, a centuries long ambition and dream was fulfilled,¬†the Great Union was decreed¬†and the Romanian Kingdom¬†became what was then the largest territory that was ever united within its borders and under its name. It integrated present day’s Moldova, and several other smaller Romanian speaking territories, that are today part of Ukraine and Bulgaria.

It then took it’s first steps towards a sovereign democratic nation with a new 1923 constitution sponsored by¬†King Ferdinand I¬†that was deemed the most fundamentally democratic constitution in Europe at that time.

In the greater European context, the end of World War I also marked the end of four empires (Austro-Hungarian, Ottoman, German and Tsarist) and created a spectacular reconfiguration of borders in which a few other nations were reborn (Poland) or created altogether (Czechoslovakia, Yugoslavia).

Since then, a tumultuous century marked several major dramatic events that shaped Romania into what it is today.

  • the conclusion of The Second World War and the soviet occupation triggered the massive territorial losses that can be seen in the map above, and the end to Romania’s constitutional monarchy.
  • the 50+ years of communist rule that followed remains a dark period with profound impacts in every aspect of life, culture and faith. The socialist atheist state attempted to rewrite history, reshape its subjects into “a new type of man“, and imprisoned, tortured and murdered many of those who were perceived as political opponents or dared publicly object to their dialectical materialist agenda – including some of the key personalities that organized this very Great Union event we’re commemorating today:
    • Iuliu Maniu – a great man and political personality of the communist opposition
    • cardinal Iuliu Hossu – Greek Catholic bishop, and the man who officially read the Union’s declaration this day in 1918. In 1948 he refused a forced merger with the corrupted Orthodox Church which bent to the will of the red terror. He paid with his freedom and died in captivity.¬†Interesting fact: he is related to me – my paternal grandfather’s sister was married to his brother Traian Hossu. Among many others,¬†Alexandru Rusu, also a Greek Catholic bishop, and my great grandfather’s brother, also died in prison for the same opposition to become instruments of the stalinist deep state.
  • 1989 brought a sweeping change across the eastern block and the bloodiest revolution behind the Iron Curtain – it toppled the totalitarian regime of Nicolae Ceau»ôescu and marked Romania’s first steps back towards democracy in modern time.¬†I was just 5 years old at the time.
  • with great expectation joined the¬†NATO alliance in 2004, and in 2007 the¬†European Union.

What’s a Romanian guy doing in the USA?

I ended up coming to America as a student in 2003, my F1-visa dubbing me an “non-resident alien”, a far cry from a proud patriot of the only Eastern European nation with Latin origins, but at least not an invader on a boat or migrant caravan seeking wellfare. Being an international student meant I had to be enrolled full time and pay out-of-state tuition (think 2X+). I covered that and my personal expenses doing occasional construction helper jobs like remodeling, digging plumbing trenches in Arizona’s 115¬įF hot summers, and laying tile in estates around Phoenix metro – perhaps not my parent’s dream job who had other aspirations for my university years – but all this to avoid being a burden to my beloved aunt (and only relative), who offered me free housing this entire period. By dramatic turning of events and nothing short of a divine miracle, my family was granted a rare type of immigrant visa in 2006 and I was narrowly qualified in that transition just before turning 21, receiving a Green Card which was a huge relief to my financial burdens as a foreign student. I was now a “permanent resident alien”, a clear upgrade from my previous status and a mere 5-year wait for the final upgrade to citizenship. I was now able to find my first programmer job at a real company, making at least double hourly while sitting in an air conditioned office, another miracle for me. The rest is history – I achieved my goal and graduated from ASU¬†without student loans or debt, married to another Romanian immigrant, became the father of two wonderful boys, and last but not least created LowPowerLab and lots of happy customers along the way. Looking back at the footsteps of my immigrant journey, God was good to me and held my hand all all these years, carried me when I couldn’t walk.

Will I ever move back to the country that gave me (and you) so much?
I can’t say yes, but I sure can’t say no either. When I was 19, it was easy to pack everything I owned (not much – mostly clothes, books, small personal effects) in my 2 free allowed suitcases, take my personal $200 savings and hop a plane to a new place with better prospects – if all failed I could return to my previously well planned endeavor to become an engineer in my own country. Things look a bit different now – if not larger suitcases, it would take a lot more effort and arrangements to move a whole family to a new system and way of life and start everything from scratch – at least not without a major reason.

I wrote this up because it’s a centenary¬†that won’t happen again in my lifetime, and thus an excuse to break and pay some tribute to history, brag about my heritage and share a bit of how I got where I am. If you’ve read this far, I thank you and I hope my story and my native country’s history inspired you and made you a bit richer in some small way. I will leave you with a few pretty images that present Romania and some of her humble achievements on this special anniversary, and the sounds of its unique language (which unfortunately were left untranslated by the creator), and hence perhaps one day you may want to uncover Romania on your own, just as Rick Steves or Peter Hurley did recently.


Portable RaspberryPi IP Camera Monitor

RaspberryPi projects are always lots of fun, and when combine it with displays, 3D printing and Moteinos, the result can only be awesome!

I had an older RaspberryPi and a touch display, and I wanted a portable IP camera monitor which I can mount or move anywhere. You can build a similar portable display, it will run on battery up to a few hours depending battery capacity – and it will automatically safely shutdown if the battery dips below a programmable voltage. It’s a nice convenient way to monitor your smart home interface, or an IP camera, weather or whatever else.

I had to find a suitable case and this adafruit one was almost perfect as-is. But who uses a Pi with a hard power switch? I wanted to use my own hardware (MightyBoost + Moteino) for battery power and backup, as well as a convenient power and reset button, I had to mod the case and add some holes to make everything fit. I also added some tripod mounts so I could mount this on a tripod or hang it from a shelf or a cabinet. Read on for the build details. I also put together a guide that will be maintained with any future changes to this project.

Continue reading

CurrentRanger: auto-ranging current meter

I’ve always wanted a fast auto-ranging low-burden voltage current meter. You may find expensive high end bench meters which can auto-range they may be slow or lack the bandwidth to capture fast dynamic loads that go through several orders of magnitude of current consumption. Most multimeters also have a large burden voltage, which means their internal current shunts can cause your DUT to see a very significant voltage drop.

I own a ¬ĶCurrent GOLD from EEVBlog¬†which is great in that it has the precision and bandwidth to capture fast current transients, but it’s a simple manual device that cannot auto-range and unfortunately it’s really noisy in the nA range where it picks up mains noise and it’s unusable without an extra cap on the input (I thought mine was broken but this problem is also reported in the EEVBlog forum here and here). It’s useful when you know your DUT is going to stay in 1 range or if you can predict when your DUT might wake up from deep sleep and manually range just before that happens but it’s a guessing game. Hence the mechanical switches get a lot of abuse and wear, add output noise during switching, and introduce some contact resistance with noticeable effect in the mA range.

Looking around, I couldn’t¬†find much else in terms of affordable fast auto-ranging and highly precise ammeters. So over year ago I started to design my own version of a current meter that has the precision and bandwidth, can auto-range, and has some extra nice-to-have features like:

  • Low pass filter for smooth oscilloscope tracing
  • Unidirectional measurement mode by default for maximum measurement range
  • Standalone OLED display
  • Bluetooth logging would be nice
  • Buzzer for tactile feedback (and why not also play some Beethoven on power-on)
  • Auto-power-off to spare the battery, oh how I craved this simple feature
  • LiPo powered, rechargeable, easily re-programmable – wouldn’t all that be great?
  • Great value vs. features without breaking the bank

It was a bit ambitious and immediately became obvious that this needs to be digitally controlled by a microcontroller to do all that. Five prototype revisions and a year later I think the result is finally ready for release. So I’m pleased to introduce the CurrentRanger,¬†click here for full specifications and user guide.

As a side story – out of the birth pains of the CurrentRanger, resulted the Moteino M0 which uses the same SAMD21 ARM processor that controls the CurrentRanger.

The CurrentRanger is now available in the shop. Please let me know if you did something interesting with this meter. It’s certainly a complex device with a large BOM and lots of parameters to test. With your help I think it can be made even better in so many ways. As resources/code/new features become available they will be added in the CurrentRanger Guide.


New products: M0 Breakout boards

There are now a few more breakouts available in the shop. With the release of MoteinoM0 I also wanted to make available a few boards specifically designed to mount flat on the M0 PCB for a super compact wireless sensor platform.

The new boards include a BME280 Breakout featuring the same sensor as on the previous WeatherShield

And there is an all new LSM9DS1 9DoF IMU Breakout featuring 3 sensors in 1 compact chip (acelerometer+gyroscope+magnetometer):


And here’s a mini SD-Card Logger Breakout featuring a low power switch to keep that hungry SDCard off when not in use.

You don’t even need to use pins at all, just solder the castellated side mounts (aka half holes). You may later desolder these with hot-air or a wide chisel tip on your solder iron. You can of course use these on a breadboard or with any other Arduino/dev board. You can also stack all these on a single MoteinoM0 if you’d like, just need to get a little creative with stacking them to keep pins connected correctly:

Details and sample code were added to the guide page.

Weekend Project: Wireless Microscope Light Ring

I have an Bausch & Lomb optical Stereo-Zoom (SZ4) microscope which is a great instrument and not a luxury when you do a lot of SMD prototyping and repairs. The light solution for this was a simple piece of white LED strip powered from a 12V adapter, worked well for over 6 years and I thought an upgrade to this will make a nice weekend project.

To really make this nice and portable it had to be very compact, wireless power from a rechargeable Lithium-Polymer battery. But how can this be powered from 3-4V when the LED strips require 12V?

Watch the details in the video below, along with a demo of laser-cut SMD stencils and complete hand assembly and test of the new light ring.

The before and after shots:

The design files are over at Github. Are you planning to make one or add more features? Did you learn something new from this video? Have a question or other suggestions? Let me know in the comments!

Transceivers In-Depth Overview

I prepared a complementary video to cover all the basics of the LoRa and RFM69 transceivers used on Moteino boards. I concentrated on the most common topics I’ve seen show up in the forum and in support emails. This should be a good primer for those getting started with using sub-Ghz transceivers with Arduino or Moteino or even other compatible boards, since most principles apply the same way. Feedback and comments are welcome.

Pick and Place Nozzle Demagnetization

Since my LE40-V Pick & Place machine’s factory PCB holder is difficult to use, has no support, and is not well suited¬†for V-scored panels, I had to get creative and¬†use neodymium magnets on a metal plate to hold the PCB panels steady during placement.

This makeshift solution got me in trouble and it’s the second time I managed to get a¬†neodymium magnet on the tip of an expensive SMD pickup tool.¬†In my last post I showed how I upgraded from magnets to 3D printed magnetic brackets to make the PCB holding task easier and avoid this problem. Otherwise this would also not be a problem if I were’n using magnets, yes I know. Or if these tools were machined from a non-magnetic tooling alloy, such as what’s used in these excellent $5 CHP 3-SA tweezers. Don’t ferromagnetic metals get magnetized over time from extensive use anyway? I think it’s common sense to use a quality non-magnetic tooling alloy in such expensive tools which will last the life of the machine and won’t develop such problems.

The workaround I found to work and save the magnetized nozzles is shown in the video below. This method should work for other types of tooling.

New Dipole Antenna Review & How-To

I’m pleased to introduce a new version of the PCB Dipole Antenna, a significant upgrade from the previous version. This has a nice VSWR of almost 1.0 at both 868Mhz (at default 78mm length), and 915Mhz (trimmed at 73.5mm). It could be trimmed anywhere down to 2.4Ghz but it will be a best performer for the wideband LoRa and FSK radios in the sub Ghz ranges. Be sure to check out the dipole section in the RF-Best-Practices Guide for more theory on the dipole antenna.

3D printed magnetic holders for pick & place

The LE40V pick & place PCB holders consist of 2 adjustable brackets that are meant to hold the PCB tightly on 2 sides (let’s call them TOP and BOTTOM) while the machine pounds the panel with parts. Typically you’d set the TOP side bracket to a fixed position that is perpendicular to the machine rails and only adjust the BOTTOM bracket depending on the PCB panel size, and hope you won’t snap your freshly solder pasted panel in half when you tighten it in. Also worth noting that by default there is empty space (ie. nothing) below the PCB for support, so I had to add some supports to stop panels from vibrating during placement. While this bracket is perfect for holding trays and very rigid panels, after only a few uses it becomes obvious this is a pretty terrible design for scored/thin panels which buckle under the 2 sided pressure and un/screwing hex nuts every time a new size panel goes in the machine gets old super fast. And yes – I snapped V-scored PCB panels to pieces on more than a few occasions thanks to this mechanism.¬†Now being a super awesome customer oriented company, DDM Novastar will surely take note and improve the PCB holder immediately, maybe using the ideas below.

After some time I added a rigid metal sheet base to properly support panels in the machine during placement and that allowed using magnets to hold the panels instead, a no-brainer makeshift solution. That worked pretty well¬†for a few years but strong magnets are not easy to handle. I thought maybe I can really fix this with a new magnetic bracket and shoot a video of making it happen. The result is below. I am quite thrilled with these holders that can secure the panels quickly and are a snap to adjust without overlapping much PCB area. Here’s a video showing how these work and how I modeled the parts:

You can find the models on Thingiverse or download a Zipped archive below.