June 2020 – VoltLog

Choosing, Placing and Routing A Shunt Resistor | Voltlog #313

If you are looking for the correct way to select, place and route your current measuring shunt resistor on a PCB then stick around as I will be sharing a bunch of tips & tricks that I learned while designing and building my own boards over the past years.

A shunt resistor can be used in multiple ways but for the purpose of this video we are interested in using it for measuring current, this means it needs to be inserted in series with the device under test. It can either be inserted in a high side configuration as shown in this example but it can also be inserted in a low side configuration. These two typologies have their advantages and disadvantages.

Here is a side by side comparison, when used in a low side configuration there is a ground offset which depending on your application may or may not pose problems. When used in a high side configuration, you must use a differential input amplifier for sensing the voltage drop while in a low side configuration you can get away with single ended.

Another thing that might be important, in a high side configuration you have the ability to detect a short on the load, while on the low side configuration you can’t do that. Also in a low side sensing configuration, you are not able to sense and account for additional leakage currents through stray secondary paths from the load to ground. This list might not be complete, there might be other differences to consider, these are just the ones that I had to consider in my designs.

But let’s say you’ve figured out the topology you want to use and you are now faced with choosing your current shunt resistor. Can you just pick your typical metal film 1ohm resistor from your favorite distributor? You can, but you won’t get the best results. Probably the most important factor you want to consider when choosing your shunt resistor is the temperature coefficient or the temp co as engineers like to refer to it. This will tell you how much your resistor value is going to change with variations in temperature.

Every system you build will probably see a variation in temperature at board level and so if you calibrate your system to calculate the current for a given resistor value and that resistor value changes with temperature, you are going to introduce significant errors in your measurement.

Why Did I Get A New 3D Printer? Ender 3 Pro | Voltlog #312

If you would like to hear why I switched from the Creality CR10 to a Creality Ender 3 pro join me in this video, I’ll share the reasons for which I made the switch as well as talk about the improvements Creality made to the standard Ender 3 to become the Ender 3 pro. But first, let’s do the unboxing.

Inside the box everything is well packaged and protected with foam but compared to the CR10, the Ender 3 is less assembled to say so, there is more assembly work for us to do, if you are in a hurry that might be an issue but for me I actually like doing a bit of assembly work on a new gadget.

While doing the assembly I took a look at the supplied sd card and I also found an assembly video with english captions, it was well made and easy to follow. There are two extra steps I did during the assembly, #1 was to take off the power supply protection cover and made sure all connections are nice & tight and the voltage selection switch is in the right position #2, the lead screw comes already greased but in my experience with the CR10 that type of grease will attract dust on the lead screw which will turn into this black gunk over time. So I cleaned the existing grease with some isopropyl alcohol and a toothbrush and at the end I applied some dry PTFE lube to the lead screw which in my opinion is better suited for this application.

InTheMail | Voltlog #311

Welcome to a new InTheMail, the series that will touch both your passion for electronics and your bank account at the same time. We have a selection of different items in this mailbag video and before we get started I would like to mention that packages started flowing in around 1st of May and things are moving, certainly not as before but there is some movement at least and I hope you guys are benefiting from the same improvement where you are located.

I’m gonna start with this multi-functional charger from LiitoKala, it’s model number Lii-402 and I actually have another one of their chargers but it’s the model with an LCD. I’ve been using that one for the past few years, it’s been working great but I needed a second one to increase the number of cells I can charge at the same time. I picked a simpler model this time, with just some LED indicators, it’s good enough for me, I mostly just plug in the cells and let them sit in there for a few hours before I return and take them out so I don’t usually check the information on that screen anyway.

This model takes a micro usb input 5V 2A so those 10W can then be distributed as mentioned on the packaging, 0.5A times 4 or something in between if you charge less cells at the same time. It can charge Ni-MH, Li-ion, Li-Fe and the battery slots are universal, they can hold a bunch of different types of cells so it’s a pretty useful charger to have. I got this one from banggood because it was in the EU warehouse but you can probably get it cheaper if you are willing to wait 1-2 months for delivery from China.

ScopeShunt Visualising The Current Waveform With Your Oscilloscope | Voltlog #310

We usually use an oscilloscope for visualizing a voltage over time but sometimes it’s also useful to visualize the current waveform over time. The right way to do it is to get a current probe which can sense the current and convert that to a voltage that the oscilloscope can display however such devices are pretty expensive, they can be around $1000 even for an entry level one like the Rigol RP1001C which is only rated up to 300KHz bandwidth.

But we can improvise something for a much lower cost and it should allow us to visualize the current waveform on the oscilloscope. You’ve probably seen me use a shunt resistor when testing power supply to take a look at the current waveform. Because as you know passing a current through a resistor will generate a voltage drop.

That voltage drop is directly proportional with the passing current and with a round value resistor we can have an easy to use transformation ratio between voltage and current. All we have to do is o introduce this resistor inline between our power supply and the device under test

For example if I have a 1ohm resistor, we have a 1:1 ration, for each mA passed through that resistor we will have 1mV of voltage drop that our oscilloscope can display. Such a circuit will of course have it’s limitations, for example it won’t work very well when testing low voltage low power devices because our resistor will introduce a burden voltage, which will drop our supply voltage to the device under test. This is also not an isolated measurement so it might not be safe when connected with higher voltage circuits.

But there are still a lot of scenarios where you could use this successfully on the electronics workbench so it might be worth building something like this. I want to make this nicer by building it inside an enclosure with the required bnc connector for connecting to the oscilloscope and 4mm banana plugs for passing the current through. I picked this small aluminium enclosure which would be enough to house the resistor, actually the resistors, because there are several advantages to using multiple resistors in parallel.

Alternative to this simple shunt resistor measuring method include the Joulescope which is a fully featured dc energy measurement test instrument with incredibly wide dynamic range that allows you to capture the smallest currents next to a jump to a higher current. I reviewed the Joulescope in Voltlog #211.

InTheMail (Survival Gear) | Voltlog #309

Welcome to a new InTheMail, my usual introductory line would say this is the series that will touch both your passion for electronics and your bank account at the same time but in this episode it’s not about electronics, it’s mostly some outdoor / camping / surviving gear that I got for my adventures and I think some of you may find this interesting, especially as our social behavior is changing now and during this summer we might spend more time in the nature.

I’m gonna start with this paracord rope, it’s 4mm wide, 30 meters long or 100ft with 7 inner strands. It’s rated for 550 pounds or 250Kg minimum breaking strength so this would work for anything when you go outdoors, tying stuff around your camp, tying stuff for transport, but obviously not recommended for anything where your life might depend on it. I try to keep this stuff in my backpack whenever I go camping because it’s pretty light and compact and you never know when you need to improvise and tie something down. The particular seller where I got this offers it in 250 different colors and styles so there is plenty to choose from.

Dual Gear Extruder Grinding Itself Problem | Voltlog #308

Welcome to another video about my 3d printing adventures, as you may have seen in a previous mailbag I got myself one of these dual gear extruders to upgrade the standard one that my CR10 came with. The original plastic extruder was working fine initially, but as time passed, the wear increased and it started slipping, the spring was not providing enough tension anymore so it was time for an upgrade.

The dual gear extruder was the obvious choice because it’s affordable and it’s dual gear system should ensure better grip on the filament. I’m not 100% sure but I believe the original design was done by Bondtech and I most certainly got a cheap clone of that from aliexpress. You would think that for such a simple mechanical device it shouldn’t matter if it’s a clone or not but as we’ll see in a moment it does matter as subtle changes can make it better or worse.

I installed my new dual gear extruder, I didn’t make any video about it, didn’t think it was interesting enough and I needed to install it without further delay because I was doing this while I was printing face shields and I needed to have the printer up and running ASAP. It was working great, I printed a bunch of face shields, it had a good grip on the filament but a few days later I accidentally noticed there is a bunch of residue gathered up on the mechanism.

8W Rechargeable e-Cig Soldering Iron Review & Teardown | Voltlog #307

These days there is a wide choice of portable soldering iron and I think very few people still consider gas powered soldering irons who were quite popular 10-15 years ago because of their portability.

Now you can get USB powered soldering irons like this one for about $6, it’s rated for 8W, takes a 5V USB input and you can plug this into any power bank and fix a solder joint remotely. I’ve used this a couple of times while doing some electrical work on a car and it was very convenient.

You can also get more powerful, more polished soldering iron like the TS100 which normally takes a DC input from a laptop power brick in the 20V range but since USB Type-C with Power Delivery is a popular thing these days, you can also power it from a power bank capable of at least 12V. But this will be in the $50-60 range and you need to purchase a special power delivery trigger cable separately.

However today’s video is not about these two options, I’m gonna show you something that fits in between these two. It’s delivered rather impressively in a cheap plastic bag but let’s see what we get in here. Looks like they included a small amount of solder wire, that’s nice, every soldering iron should come with a small amount of solder. We get one of these small foldable sheet stands so you won’t burn something when setting the iron on a surface. This looks like our soldering iron tip and inside here we must have the soldering iron body itself and a charging cable

Wiistar 1080p 60fps HDMI USB Capture Card Review & Teardown | Voltlog #306

Ever since I got the new microscope and HDMI camera setup I was thinking of ways to capture video on my computer from the microscope camera. This particular camera is the Hayear 34MP model which I reviewed in Voltlog #292, it outputs 1080P at 60fps over HDMI and it does have on-board micro-sd card recording, so I could record images or videos to an sd-card but if you want to live-stream the camera feed, a capture card is needed on your computer. There are countless options in terms of capture cards but as usual I tried to find the cheapest solution that does the job well enough.

This particular unit came up in my searches, it’s relatively inexpensive when compared to other options that advertise similar specs 1080p at 60fps, it has two hdmi ports, one is an input for capture the other one should be a pass-through so you can connect a monitor at the same time of capturing video but we’ll see if that function works as advertised in a few minutes.

We have a USB Type-C connector for the computer side and an audio output 3.5mm jack. It is mentioned in the product page that it’s supposed to have a delay between audio and video so I’m guessing it’s related to this audio output port. The enclosure is aluminium which should help with heat dissipation and this particular unit is branded Wiistar but I believe you will find this under other names as well. Inside the box you get a USB A to Type-C cable about 1m long, a small usb A to type C adapter, a disk and a user manual.