Arduino Programmable Constant Current Power Resistance Dummy Load 1. Steps. Dont let the intro image scare you I explain it all in this step. If youre new to electronics and electrical theory in general, this step will guide you through the theory behind it, how it works and why. If you have been doing electronics for a while then it may be worth skimming over this article just to refresh your memory and see what principles are used. Most electrical theory falls back to good old Ohms Law,V I x RV Voltage I Current R Resistance And this dummy load is no different, in fact, there is only one other formula used in this whole project, and that is,P V x IP Power V Voltage I Current. Thats it pretty easy really. Firmware Version 3. Update Logs. New. Added exposure control in the mode PASM for video capture Added AFMF control for video capture. Added RAWJPG format. The way that this dummy load works is that it uses a MOSFET more on MOSFETS in a minute as a big variable resistor to control how much current is let through the system. By sensing a voltage and feeding that back to the MOSFET via an op amp more on op amps later also it knows how much current its letting through and adjusts its internal resistance accordingly to maintain the current its supposed to be letting flow. If that sounds a bit confusing, stick with it and it will make more sense as we go on. The flow of electricity can be closely compared to the flow of water, think of the voltage as the pressure of the water, the higher the pressure the more you can do with it, for example, a high pressure water cleaner, will clean much more dirt and use much less water than a garden hose doing the same job. Think of current as the flow of water, the more water you have flowing the faster you can fill the bath. Think of resistance as a kink in the hose, when you put a kink in the hose you need a much higher pressure voltage to push the same amount of water current through the kink. Think of power as the bath tub, regardless of your water flow current it will still take the same amount of water power to fill the bath tub, the faster the flow higher current the faster it will fill and vice versa. In our dummy load, the key component is the kink in the hose, the MOSFET. Over The Air Update Arduino Firmware' title='Over The Air Update Arduino Firmware' />We need to control that resistance kink to maintain the current flow at our set value, regardless of the input voltage pressure. You may be wondering what a MOSFET is or what it is used for. A MOSFET is like a variable tap, we can send a voltage to it, known as a gate voltage, and this changes how wide open the tap is. There are two main types of MOSFETs, an N type and a P type. This article does a very good job of explaining the difference between the types and what they do. This load uses an N type MOSFET to control the current. In general, A MOSFET has three pins, the gate, drain and source. The drain and the source can be though of as the hose and the gate is like the tap valve. In the case of an N type MOSFET conventional current flow is from the drain through to the source, I know that seems a little confusing but it is because of the actual electrons flow, we wont get into that here as it can confuse you Lets just consider conventional current flow for now. In the case of our N type MOSFET, the higher the gate voltage the wider the tap is open, the closer to 0 V the closer that tap gets to closing. As you can probably imagine we need to adjust that resistance kink very quickly to ensure our current is as stable it can be. Because of this, we cant rely on the microprocessor to sense the current, calculate what the current should be, calculate what the resistance should be to get that current, convert that to a voltage the MOSFET needs to be set at that resistance then send it to the MOSFET. Way too long Way too unstable To over come this issue we bypass the micro controller all together and use an op amp to do all the hard workimage 20171004 Update If the flashing method in this first post does not work for your device, try the method mentioned in this post 20170510 Update Sonoff. Thats the end result, for now. The rest of this post will share the journey I took in building this toy. Perhaps it will inspire you to follow along, or to build. An advanced quadcopter with full GPSguided autonomous capabilities. Iris is designed to provide an outofthebox flying experience that brings the power of. Before we get onto the op amps we need to cover one more aspect of the circuit and that is those 1. R1 R1. 0. They are 1. If you where to put a multimeter across those resistors it would read 0. Why 1. 0 why not just 1 0. Well for three reasons. Accuracy Power Dissipation Cost. The reason we have improvement in accuracy is because that 1. One thing we havent really looked at is power. As current passes through a resistor it drops voltage drops pressure as it passes through a kink this drop in voltage is known as power dissipation, power can be many things, in this case, its heat. Many things rely on heat off resistors, your kettle, bathroom heater, hair dryer, hot water service and the list goes on. In this case, its an unfortunate by product. However, lets just do a few quick calculations on how to calculate just how much power is there. UPDATE Lets Make Robots, my home digital hackerspace, was purchased by RobotShop. I dont want to go into, but the new owners banned myself and most of the veteran. NodeMCU V2 ESP8266 ESP12E Flashing Update Firmware using esptool. Python in windows CMD Tutorial 2. How to flash or upgrade NodeMCU V2 v1. ESP 12E. Glad to see you have arrived on this page to learn how to build a programmable constant direct current dummy load. This load will allow you to draw a set current. I love how damn near every product is now explicitly marketed for, if not tailored to, Arduino. Guidestutorialsetc. On Sunday,jcwebcreative, Beijing Guoan will be at the workers Stadium usher in the new seasons first home game. As in the first round of the road 2 to 0 victory over. This load is capable of carrying 8 amps, lets first work out how much voltage we will drop across our sense resistor of 0. V I x R 8 x 0. Now we know how much our voltage dropped we can work out our power dissipation. Over The Air Update Arduino Firmware' title='Over The Air Update Arduino Firmware' />P V x I 0. Let me tell you, thats quite a lot of power dissipated from one resistor Which brings me to the other element, cost, one 0. Download Videos From Internet Link. The purpose of these sense resistors is it allows us to accurately measure the current in the circuit against a known resistance, no mater what, ohms law always applies, as we have shown, if there is 8 amps going through a resistance of 0. Like wise, if we put 1 amp through the 0. Try it, put any value of current into the above formula and you will get a proportional voltage drop across those resistors. Remember this, we will see why thats important in a little while. OK, Op Amp time Op Amps can be very complicated beasts and we are certainly not going to cover all aspects of the op amp in this instructable. If you wanted to read a bit more into the op amp then this is a very good tutorial to explain them in detail. For this project I have used an LM3. U2a LM3. 24a. On most op amps there are 5 pins, a non inverting input pin 3, an inverting input pin 2, an output pin 1 and a power supply pins 4 and 1. One important property of the op amp that we need to consider is that it will do everything it possibly can on the output to try and keep the inputs at the same voltage. The op amp hates having a difference of voltage on the input. In fact this is very important to understanding the inverting and non inverting amplifier circuits. The dummy load makes use of this very useful feature of the op amp to control the MOSFET gate the kink in the hose so that it can keep the current to the level we set. How does it know what the current is By reading the sense resistor. Lets have a look at that for a minute, in the image above, the sense resistors are R1 to R1. That means, if we have 0. We are finally getting to the fun part Now, if you have a look at the circuit above, the top of these resistors feed back to the inverting input of the op amp It does go through a few other resistors and capacitors but please ignore them for now, we will talk about them in another step, trust me when I say, that 0. You will also notice that the gate of the MOSFET M1 BUK9. R8 6. 0E is connected to the output of the op amp. Going back to what we said earlier, that the op amp will do everything it can on its output to keep its inputs the same, so with that in mind, if we set a voltage of 0. So, it will put as much voltage as it has to on the gate of the MOSFET opening the tap to open it enough so that 1. A flows. Likewise if we set 0. That is how it works, what ever voltage you set, it will drive the MOSFET enough to get the same voltage on the other input.