Current Ranger R3 released!

CurrentRanger is now at revision R3!

I received great feedback and several threads in the forum outlined some patterns of user behavior which led me to make some improvements and hopefully eliminate some of the issues I’ve seen people run into. Here is the change log:

Reverse polarity protection

Perhaps some folks were too excited to turn the CurrentRanger on and missed double checking their battery polarity and pufff .. the charger chip released the smoke. I offered free fix/repair to a few who’ve asked, and to put this behind – R3 now ships with reverse polarity protection. If you get it wrong, nothing happens, including the obvious – won’t turn on!

Redesigned 3D enclosure

The previous pillar style enclosure takes about 1h05m to print. And because of the way the mounting pillars are placed in R1-R2 the case called for PETG (stronger less brittle material) but often produced diagonal drag lines in the inside-bottom of the case, and PET tends to print stringy which requires additional cleanup. Mounting screws are now moved closer to corners, this yields more PCB area and allows the case to have top corner posts which are a lot more practical, free the bottom of the case for a larger battery and shave a whopping 18 minutes off the print time. This also yields more room for enclosing a bluetooth module inside the case while keeping the case low profile. And the case print just looks that much better in PLA (no posts that can easily snap either). I’m really happy about this improvement.

Gold terminals be gone!

I am done with Gold terminals, they are the fake news of banana terminals. There is nothing truly gold about them. I tried to like them but frankly, I found them to be more trouble than their gold appearance is worth. Being exposed makes them a short hazard, and twist-locking wiring actually rips the wires. Besides, I almost never use the input terminals since I added the green thumb terminal which makes it a snap to insert battery and project wires. Those gold terminals looked rich and fancy (until the “gold” wears off revealing the dull communist metal) and that’s where the “goods” stop. And yes – I did try many different vendors, I could not find a vendor with consistent quality and repeatability. They may be good for your speaker where you never touch and see them again, but I think not suitable for an electronic instrument.

You want Gold(less) terminals on your CurrentRanger? Be my guest, get them from wherever you can, but I won’t ship these anymore. I cant put fake on awesome. Instead the kit is now standard with low profile banana terminals – simple, compact, functional, consistent, just as or more conductive, that’s real “gold” in my e-tool box.

Moved components & features

A few folks in the forum reported damaging/snapping some of the capacitors near the input terminals, causing the unit to behave erratically – these are now moved away from the terminals to help reduce the chance of this happening. Just to give you an idea, here’s what that looked like, and what to avoid doing when mounting mechanicals around small SMD components on any board:

Misc other changes & additions:

  • the power button is moved slightly left to allow easier access when OLED is mounted
  • the charge LED is now moved next to the USB and is see-through just like all other board LEDs
  • the Bias LED is moved symmetrical to the LPF LED
  • a GND pin added to the SPI header next to the lower right mounting hole
  • minor layout changes & silkscreen additions

Silkscreen nightmares!

Since the top of the PCB serves as the user interface, the silkscreen needs to look fairly good and crisp. I went the extra mile to try and design some nice graphics and make a PCB with a bunch of traces look more attractive and professional.
Unfortunately since inception I’ve had numerous silkscreen issues because of these graphic elements (some my fault, some the fab’s fault, and some “in between”) causing several batches of panels to go straight into the trash. I painstakingly retraced all these graphic elements on the board in a vectorized form and these issues are now resolved (as far as silkscreen design goes). The fab can still screw up but hopefully that won’t happen again.

The official guide is updated, as always please read it carefully before using your unit. Here’s the SMD side:

CurrentRanger is made with great love and pride in Michigan USA, and I welcome feedback, suggestions and contributions.

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!

Availability

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!

Pricing

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 🙂 – 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.

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 µCurrent 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.

Enjoy!