REJOE Power monitor EMK850S+ Review & Teardown | Voltlog #415

Welcome to a new video, this will be a review & teardown of this power profiler device so this can be useful if you are trying to measure the power usage of a particular board that you are working on. It can internally generate an adjustable voltage power supply rail which it outputs on these terminals, you use that to power the device under test then by using the supplied PC software you can analyze the power usage of your device in great detail. 

As you may remember I also have a Joulescope which is an awesome piece of equipment, high resolution, high dynamic range for doing the same kind of analysis but it does not include the power supply. This guy with its included power supply is closer to something like an otii arc, cause that one also include the power supply so I might make some comparisons in terms of specs with these devices during the video.

Inside the box you get a power brick which feels low quality, a mains IEC cable with an adapter for European plugs, we won’t be needing these as I can use my own IEC cable with the proper plug, and a set of short test leads with banana plugs and J clips, The cable feels nice, flexible but the connectors are of low quality and you are likely to encounter problems if you will be using this types of clips long term so I will be replacing these as well. In my opinion, instead of including cheap test leads, you might not include any at all. Saves the final user the trouble of dealing with bad test leads.

The front panel features the two output banana plugs widely spaced apart, two rotary encoders crammed together and a couple of 7 segment displays for voltage and current so that you can get readings independent of the PC app. On the back we get the DC 12V input and the USB connection for the computer plus an on/off switch. They had plenty of space on the front panel so I think it would be nicer to have the on/off switch on the front. And the two potentiometers spaced wider apart. The model number for this unit is EMK850S+.

They don’t tell much in terms of specs but they mention Input Voltage 12V DC, Output voltage 0.5-12V,

Measure Range: 0.1μA – 2A, provides μA resolution current measurements with a sample rate of up to 10 ksps. No claims on accuracy as of now but maybe they’ll add those later, as I said this is a new product. If we compare it to the joulescope which has a 2Meg sample rate and 1nA resolution the TechRejoe unit is clearly lower specced but also less expensive

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.

Voltlog #280 – TPS62840 olmBoard Ultra Low Power Step Down Converter

Welcome to a new Voltlog, in this video we are taking a look at the TPS62840 ultra low power step down converter from Texas Instruments. It’s basically a buck converter with an input voltage of 1.8-6.5V, 750mA output current, with a quiescent current of just 60nA and active current of just 120nA. It also features very good efficiency at light loads of just 1uA it can offer 80 percent efficiency.

Other features include 16 selectable output voltages through an external resistor and a stop pin which when activated will completely stop any switching to eliminate any switching noise for a short moment, allowing you to take for example an ultra low noise measurement during that time. During that take power will be sourced from the output capacitors. So it looks like this is a pretty interesting dc-dc converter, with really nice features and it’s optimized for ultra low power devices.

Voltlog #257 – ESP32 PIR Motion Sensor With Deep Sleep & MQTT (revB part2)

In this video I’m gonna show the second revision of my esp32, battery powered PIR motion sensor. This second revision contains some optimizations to improve deep sleep power consumption as well as to fix some of the errors I had the first revision of the pcb.

Voltlog #240 – ESP32 PIR Motion Sensor With Deep Sleep & MQTT

Welcome to a new Voltlog, in this video I’m gonna show you how I designed and built this board which functions as an esp32 based, battery powered PIR motion sensor. So I started by designing the circuit, I used some common building blocks, I added the ESP32 with it’s bypass caps, some test points and the programming circuit with auto-reset, I then added some connection points for the PIR sensor, an RGB LED because why not have a nice way to signal this is one of those very small digital RGB leds, it’s just 20x20mm, it’s connected to 3.3V even though it’s only rated for 5V so I’m hoping this is going to work even on 3.3, it’s also worth having a temperature/humidity sensor to also sense that in whichever room the node will be placed and finally the power supply circuit which is a simple low dropout regulator with an 18650 battery as the input.

I did not include a battery charger circuit on this module, because I wanted to keep things simple, I’ll have a battery socket so I can just remove the 18650 cell and charge it separately plus the whole circuit should run in sleep for extended periods of time giving me a long operating time so i wouldn’t have to charge the battery too often.

Once the schematic was finished I did the board layout in a hurry so it’s not exactly pretty or optimized

but I tried to move the esp32 antenna to the side, to place the PIR sensor in the top side as the module will probably sit vertically, I tried to place the temperature sensor in the bottom side to keep it away from any components that might get hot and also placed some isolation slots for the same reason.

You should check-out revB of this board, I made some improvements present in the video below.

Voltlog #211 – Joulescope DC Energy Analyzer Review & Teardown

Welcome to a new voltlog, today I’m excited because we’re going to take a look at an awesome piece of instrumentation. I’ve received a pre-production demo unit of the Joulescope DC Energy Analyzer.

The joulescope is a low cost precision dc energy analyser which is currently on kickstarter so check the links in the description of the video for the kickstarter campaign because it has a massive discount from the retail price. The joulescope has circuitry for measuring voltage and current, from which it can calculate power and then it can integrate power over time to calculate energy. The current measurement range is from 10A al the way down to 1nA, that’s a huge dynamic range which makes it very useful if you plan to measure the energy consumption of a device that has mixed behavior for example an esp32 that will wake up, do some activity and then go back to deep sleep.

The joulescope works with a software companion that has a multimeter view and an oscilloscope view which I find very useful because it will allow you to time correlate measurements of voltage and current. That can be extremely useful when determining the energy usage of your device.