Voltlog #128 – LM338 Constant Current Regulator Circuit

Welcome to a new voltlog, today we are building a very simple constant current regulator based on the LM338 linear regulator. This is a very robust and stable classical regulator that is being manufactured by many big names like ST and TI, it has quite a high output current  rating of 5A continuous, it even comes in a TO-3 can package but today we’re going to use a TO220 which is more commonly available.

To make a constant current regulator out of this, is very simple, the datasheet gives us the circuit we need to use and we only need a low value resistor to do that plus the optional input bypassing cap which is 0.1uF. We’re going to use this formula to calculate the value of the resistor, so the output current is equal to the Vref divided by the value of the resistor.

External references:


Voltlog #127 – 0-60V 0-10A 1mV 1mA Panel Meter Review

So I discovered this module a few months ago and it’s been sitting in a box since then, I almost forgot about it, until a few days ago when I decided it will be a good idea to do a video on the subject.

Let me give you a few details on the specs of this module and as usual it’s pretty difficult to find the information as it’s the case with every new module coming out of China. First of all we have an input range of 0-60V and 0-10A and a 5V rail is needed to power the module itself. It has a voltage measuring accuracy of ±0.2% + 0.2% full scale which sounds strange because these figures are usually given in a percentage plus or minus a number of least significant digits. The current measuring accuracy is ±0.4% + 0.3% full scale.

The meter is basically capable of measuring with a resolution of 1mv and 1mA (however the accuracy is quite bad, as shown in the video) which is quite nice and useful (not really useful with bad accuracy) for projects like DIY power supplies or DIY electronic loads. It can also display the power in watts with a resolution of 1mW as well as showing the load impedance.

Here are some links to this product:

Voltlog #126 – How fast can you update an e-paper display?

Welcome to a new voltlog, today we are going to answer the question how fast can you update an e-paper display, is it suitable to display live updating values from a sensor for example? Some people asked these questions in the comments of previous videos so I am doing some tests to try and answer these questions.

Now there will be a big difference between trying to update the whole screen and trying to update just a small section. And that delay might also be related to how fast the processor can send the information to the display. So for example measuring the time passed between sending the first byte of data to the display and the last byte going out is not that relevant, it might just be a slow processor, and the display could accept data much faster.

Also in the case of an Arduino the ram size is very limited so a full buffer could not be implemented. This means sending of the data to the display is done inefficiently increasing the time it takes for a full update.

Link e-paper display black/white:

More resources below:

Voltlog #125 – Banggood E-Paper Display Fiasco

This is just a short follow-up on the e-paper display video. It was brought to my attention by one of the viewers that banggood is shipping the bare display instead of the module as whole display + pcb + cable.

Link e-paper display black/white:

More resources below:

Voltlog #124 – Getting Started With E-Paper Display Module

In this video I’m gonna show you how to load a custom image on the e-paper display. Let’s see how easy it is to get started working with one of these e-paper display modules and an Arduino board.

Link e-paper display black/white:

More resources below:

Voltlog #123 – Buzzer Comparison

In this video I am measuring the output level of the various buzzer that you can find on ebay, banggood or aliexpress.


Get the UNI-T UT353 Sound Meter from these sources:

Here are all the buzzers shown in this video:

Voltlog #122 – C5W LED vs Incandescent Bulb Temperature

Welcome to a new voltlog, in a previous video I showed these C5W LED bulbs that I got from ebay they were very cheap so I put them to a test and discovered they reached very high temperature in just 15 mins of running in free air which got me concerned, the fixture of this bulb could melt.

C5W LED Bulb on Ebay 

C5W LED Bulb on Aliexpress 

C5W LED Bulb on Banggood 

Thermometer used in this video

Voltlog #121 – InTheMail

This video starts with a rant about how bad the postal system is around here(Romania).

Here is a list with links to all the items shown in this video:

Voltlog #120 – Mini DC Power Supply Review

So I guess a gadget like this is worth 10$ because you could replace that linear breadboard power supply with a more efficient one, which will give you voltage and current display as well as adjustable output.

Here are some images I took during the teardown of the mini power supply:








Checkout this power supply from the links below:

60W Electronic Dummy Load Battery Tester:

Voltlog #119 – NEW 150W Dummy Load Review

Today we are taking a look at yet another electronic load. I found this one on Aliexpress, I think it’s a rather new model so let’s see what it can do.

Here are links to the 150W and the 180W version of this dummy load: