The only feature that is missing for me here is battery level indicator, for which we could use this lipo battery voltage, tester that I got a for cheap from eBay and while it certainly measures the voltage of each cell correctly I’m – not thrilled about this play. Since you cannot easily tell how much energy in percentage is left in the batteries, a possible and awesome solution, for that would be an LED but display. So in this video let’s talk about the classic LM ‘1 5c, whose job is, coincidentally to drive, led bothers place and, furthermore, let’s also create our own more precise, led battery level indicator circuits let’s get started Music. This video is sponsored by jl CPC, be one factor. Bottom jlc PCB focuses on rapid prototypes of one to six layer, PCBs and all of them are shipped directly from the factories after being produced a blow Dro Gerber files to test the fast speed of prototype, production and delivery. According to the datasheet of the LM three nine one, four, it is an ICU that senses analog voltage levels and drives 10 LEDs accordingly, which is basically just what we needs, since the voltage of a battery can tell us how much energy it got left. So I positioned a DI C on a breadboard and had a closer look at its typical application circuits given by the data sheets. The 10 LEDs need to get connected with the cathodes to the pins 1, 10, 11, 12 up to 18, and no, they do not require a current limiting resistor since the ICEA features constant current outputs.
This current can be set by connecting a resistor between the ref out, pin and grounds. I went with a 2 kilo, ohm resistor, which gives us a current of around six point, two five milliamps per LED. Next, we have to connect v to ground v, to the supply, voltage, ruffridge us to ground and mode to the supply voltage to activate the bar graph modes. And if you want to learn why exactly I connected those pins to either ground or the supply voltage, then I would highly recommend checking out the datasheet, since it is very well written anyway. What is left to connect are the RL o seek and our H I pins, which determine to which voltage and voltage range. The LEDs will react to learn more about it. Let’S look at the block diagram of the IC. In a nutshell, we cut n comparators to whose inverting inputs is the sake. Aka signal pin connected the non inverting inputs of the upper comparator is connected to the RHI pin, while the following one’s are all connected to the previous non inverting inputs. Through 1 kilo, ohm resistor and the last resistor is connected to the RL open. Now the signal pin usually connects to the changing analog voltage, so the battery voltage, while the RHI and our elope are connected to the voltage potential window. We want to cover, for example, if we have a look at the discharge curve of the utilized inr 18 650 25 – our lithium ion batteries, then we can see that our voltage range starts at four point.
One volts and goes down to around two point: nine volts multiply that by four. Since I got a 4s 4p battery pack and we got a voltage window of sixteen point, four to 11 point 6 volts. So we connect a 16 point, formal potential to our hie and an 11 point 6 volt potential to our ello. Due to the resistor ladder which acts like a voltage divider. We now got 10 different voltage potentials at the comparator inputs and since we know that if the inverting input has a higher voltage than a non inverting inputs, the outputs will be pulled down to grounds meaning the LED on the output will light up. It all starts to make sense as the battery voltage decreases. It reaches the 10 different resistor ladder. Voltage potentials turns the output higher and thus turns the LED off for demonstration purposes. I built up the described circuits with a constant voltage source and upon a geometer as a signal inputs and, as you can see, when the battery voltage drops the LEDs turn off one after the other awesome. You might think I will use that for my new battery pack. Well, if you want a crude battery level indicator then go for it, but for me there’s still a problem. Since we got 10 LEDs, you would think that each one represents 10 of energy in the battery pack, but that is not true. Due to the resistor ladder of the ICEA, with only 1 kilo, ohm resistors, we get a linear voltage decrease, but if we would mark those points in the discharge curve of the battery, then we can see here that it does not follow the actual line very well.
One solution for that is to decrease the voltage window so that we look at the mostly linear section of the discharge curve and while we edit, we should also set the last LED to 12 energy, which the capacity of 2.2 amp hours represents. But for me, even those changes are not enough, so I came up with my own LED battery level indicator schematic. It basically works the same way as the LM ‘1 for whippits comparators, but I only use six LEDs, no constant current methods source current instead of sinking it and can set the trigger voltage potential of each comparator stage manually through a trimmer and after I did a Small proof of concept test on the breadboard. I went ahead and sold out all the required components to piece of perf wards and connected them to one another. According to the schematic to create the constant 20 volts for the power and the trigger voltages. I also utilized a small boost converter module, which I directly sold outs to the per port and after fine tuning that it was time to adjust the trigger voltages. For that I set my lowest capacity limits to 2.2 amp hours and the highest one to obviously zero and hours. Then I calculated for linear capacity steps between those two values and marked them in the discharge curve. According to the point of intersection, I took the reading for the different voltage levels and simply multiplied them by 4 to get the right trigger voltage for the six different binary states.
Afterwards, I simply tuned the trimmers to outputs the required voltage to the comparators inverting inputs and just like that, this project was complete and, as you can see, by doing a test with my lab bench power supply, it seems like everything works like anticipators.
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