This is an awesome tutorial. I am trying to wire this up myself and want to know what the approximate voltage should be after each step in your block diagram (for troubleshooting purposes). Could you help me with this?
It is very hard to give a value for the approximate voltage after each stage, because it depends strongly on how much you are contacting the muscle. And even if you knew this approximate voltage, it wouldn't help much in troubleshooting if you don't have an oscilloscope. The signal is a superposition of AC signals, and you won't be able to read it with a multimeter, as such a device only measures a very specific frequency. Now, if you have an oscilloscope, then you don't need to know the approximate voltage, since you will directly see how the signal changes when you contact the muscle.
@@BlueMoonshine Should the voltage signal coming high pass filter be well over .7 volts? You mentioned in the video that the voltage should be too low to activate a diode with the activation voltage of .7 volts.
@@mahefred549 Yes, but actually no! As explained in the video, we are using a "precision full wave rectifier" that act as a "superdiode", that is to say a diode without threshold. So this superdiode is activated as soon as the signal is non-zero, and the signal doesn't have to be over 0.7 V, it can be much smaller.
Hi sir it's me again. Sorry to bother you. I just have two additional questions so I can finish up the circuit. The first question is: In the Schematic I can see Vp and Vn that I believe stands for Positve voltage and negative voltage... Do I use for Vp the 9v from the battery and for Vn the 0v or negative part from the battery... Or do I use the virtual ground as well.... And my other question is... For the amplifiers, in order to supply the voltage that they require, can I use the battery as well for the positive input and the virtual ground for the other input? Thank you so much beforehand
You use the positive lead of the 9V battery for Vp and the negative lead for Vn for all op-amps. The virtual ground that you get out of the LM386 is to be used everywhere you see the ground symbol on the diagram.
Good day! Thank you so much, for a great example of a self-made EMG sensor and detailed academical explanation! I have a question about C4 capacitor, on diagram you mark it as capacitor with polarization and in components list we can see, that it has 220 nF capacity, the problem is that I can`t find a polarized capacitor with that capacity, what should I do? Or maybe it is a misprint in the list?
@@BlueMoonshineOne last question. In components list capacitor capacity are 2.2uF and 220nF ?but on circuit diagram they are 1uF and 150nF. What is the best option?
1uF and 150nF is what I ended up using because I didn't have the others. This is OK as long as you use the RC combination that produces the same cutoff frequency. So, you can either stick to the values given in the diagram, or to the values given in the list of components.
THIS WAS AN AWESOME TUTORIAL , I AM USING THIS IN MY PROJECT WORK BUT HAVE AN TROUBLE IN CONNECTION OF THE BATTERY WHERE I HAVE TO CONNECT IT CAN YOU PLEASE UPLOAD THE IMAGE WHERE TO CONNECT THE BATTERY TERMINAL
HAVE AN TROUBLE IN CONNECTION OF THE BATTERY WHERE I HAVE TO CONNECT IT CAN YOU PLEASE UPLOAD THE IMAGE WHERE TO CONNECT THE BATTERY TERMINAL, AND WHAT IS THE ( SW ) IN THE SKILLSCREEN
This is what I explain at 18'30''. You make a symmetrical power supply by using the LM386. Connect the the two inputs of the op-amp together, and the battery is directly connected to it (positive on pin #6 and negative on pin #4). Then output of the op-amp (pin #5) will serve as the GND for all other op-amps. The + and - of the battery are also connected to all other op-amps of the circuit (V+ and V-, respectively).
Sir, what is the use of offset selector? , what is the role? Sorry i didn't really catch up from the vedio. Also in the vedio shows 100k pot on the non-inverting terminal but in the diagram 10k divider circuit is used can you clarify this. Which circuit i have to follow?
The offset selector allows you to shift the output signal up or down, in case the device you want to control requires a specific range of voltages. The diagram is wrong, use the circuit in the video.
Hi there thank you for this tutorial. I read the comments and figured out that you used 1uF capacitor in low pass filter with 82k Ohm, but then the cut off frequency will be f = 1.94 So how did it work ? If you can just tell me what resistors and capacitors you used in your filters because i made it and there is a problem in it
I am having difficulty understanding which connection is connected to which opamp in the diagram you shared. I want to build this circuit on breadboard first. Can you help me by clarifying these connections?
It's kind of trivial: the video shows you the block diagram, and how each block works is explained in detail with calculations. Also, a picture of the complete diagram is given in the description of the video.
Great explanation! However, I can't get my head around how the 3-point micro-switch is placed on the PCB, or even which micro-switch to use, could you help me with that please?
@@BlueMoonshine I'm sorry, on the components list one of the last items says "Sw=3-point micro-switch". That's what got me confused, thank you for the clarification!
The video logo at the beginning was made by using the raytracing software "POV-Ray", the slides were made with LibreOffice Impress, the equations were made with klatex, and everything assembled with the video editor kdenlive, all these running on Linux.
Because the potential of a single electrode is undefined. What is defined is voltage, that is to say a potential difference. So a potential is always defined with respect to some reference potential (which is unknown). When we choose this reference to be the "ground", it only means that we attribute to it the value "zero volt". But still, the current needs to flow through it, because the op-amp cannot directly measure the potential of an electrode. What the op-amp does is that it lets a small (but non zero) current flow through its inputs, and this current has to go somewhere, namely back to the ground.
Sir, one last question, in the components list there are 2 100uf capacitors to improve the stability. But you didn't put any. To improve the stability where i have to put these capacitors. And what stability was increased?
They go at the output of the symmetric power supply that is formed by the LM386. They can improve the stability of the supplied voltage, but in my case, it was not necessary.
I just don't get why you used an amplifier in the high pass filter ? Plus if we want to target more than one muscle should we use the same circuit for each muscle ?
As I explain in the video, the signal needs several stages of amplification, so I used an amplifier in the high pass filter to amplify the signal by 15. For more than one muscle, a multiplexing technique can be used so that a single circuit like that can be used for all the muscles. I will make a tutorial for that when I will have time for it. Basically, it will be a technique similar to what I use here: bluemoonshine.fun/Project-AudioSpectrumAnalyzer.php
Can i use this circuit for analysing the face muscles while we smiling. Can you help me with this. What modifications i have to change while making it?
The circuit is just a prototype that gives the method for detecting muscle activities. Everything is explained with great details in the video, so that anyone can generalize it to any particular application. I'm very busy and already spent a lot of time making this video, and I currently cannot spend more time on it.
This is explained at 17:45. The LM386 works exactly like any other op-amp. It amplifies the potential difference between it positive and negative inputs. If the two inputs are connected together, then the difference is zero, and the op-amp outputs a zero potential with respect to its midpoint between its positive and negative power pins. The midpoint between 0V and 9V is 4.5V. This is this value that we take as the "ground". The reason for using the LM386 instead of any other op-amp is that it is designed for having a zero offset voltage (other op-amps need to have it adjusted by adding some resistors) and for having a very low output impedance (which is what we want).
@@ildjaviviane1432 The LM386 is just for the symmetric power supply. It outputs 4.5 V, which is to be used as the ground. The positive side of the battery is Vs+ and the negative side is Vs-. 0V, 4.5V, 9V is the same as -4.5V, 0V, +4.5V since only voltage difference matters.
No, the LM386 is just for the power supply. It is a trivial connection, as can be seen at 17:47. Simply connect the two input pins together, the + pin to the positive side of the battery and the - pin to the negative side. Then the output pin of the LM386 is your virtual ground.
@@BlueMoonshine I understand thank you so much for the fast response... Just one more question, so then the output from the lm386 being my virtual ground will go to the ground as my reference and is the connection that is showing bellow emg1 and emg2?
One doubt, our muscle waves lie in the range of 5 - 450 Hz, then why did you take the cutoff frequency of high pass filter as 7.23Hz and cutoff frequency of low pass filter as 10Hz. Why didn't you choose the cutoff frequency of the high pass filter as 5Hz and cutoff frequency of the low pass filter as 450Hz.
By using a cutoff frequency of 7.23 Hz for the high pass filter instead of 5 Hz, you are not losing any significant part of the signal. Regarding the low pass filter, you are misunderstanding the point. The signal has already been rectified before the low pass filter, so it no longer contains "waves" from the muscles activity. The frequencies present in the signal are the frequencies at which you contract the muscle. There is no way you can contract a muscle more than 10 times per second, so any frequency above that is just noise that needs to be eliminated.
And in the offset selector step i used a 100k Ohm variable resistor the middle leg to the op-amp, and one to the 9volt battery and the last one to the groud. Is that right ?
As explained in the video, this is to have a gain that can be adjusted to a maximum of 50, which allows the output voltage to reach the maximum voltage that can be delivered by the op-amp.
Well, that's a little bit vague, as the LED is at the output, so anything between the input at the output could be wrong. do you have access to an oscilloscope? If not, it's gonna be hard to troubleshoot it.
Sorry for bothering again im asking because i made exact sensor sometimes the light goes on when i close my hand and soemtimes its always on and sometimes it doesnt work i dont know whats wrong
The gain of an instrumentation amplifier is not large enough. Also, even if it was large enough, it wouldn't work because, as I explained in the video, you need to condition the signal after each step of amplification in order to avoid a saturation.
@@tiffany-e4k It's just for the offset selector. It is to be put in replacement of the voltage divider made of the two 10k resistors at the bottom left part of the diagram, between Vp and Vn. It doesn't really matter whether it is a 10k, or 100k, or 500k potentiometer.
@@alpakbac4724 It is called "oscilloscope", not "oscillator". The frequencies generated by the muscles are in the range [5 Hz, 400 Hz]. Included in this range is the range [20 Hz, 400 Hz] which are audible by humans. So, if you amplify the signal enough and inject the signal in a speaker, you should be able to hear it. And once the signal is rectified, you should be able to see it simply by connecting an LED.
Maybe. You would need to use an amplifier that has a very low output impedance. Also, some amplifiers output an offset voltage that may be problematic. The LM386 is designed to have a very small offset voltage.
What does that mean? Vdd (a.k.a. Vcc) is just a positive supplying voltage and Vss is just a negative supplying voltage. The video gives you all the diagrams with rigorous derivations of all equations, and the circuit behaves exactly as predicted by the equations, so everything is there.
@@spock-j4e I really don't know what you are talking about. Can you show me on the diagram where and how you want to "implement the negative voltage"? Send me an email via the contact form of my website: bluemoonshine.fun/Contact.php
@@BlueMoonshine I'm talking about the negative and positive voltage connections that the amplifier requires, are they simply replaced by the negative from the 9V battery?
@@spock-j4e As explained in the video, the positive for the op-amps is the + of the battery (9V), the negative is the - of the battery (0V), and the ground is the 4.5V that the LM386 gives at its output.
@@joyelthomas598 Well, use the ones you already have. If you don't have any yet and need to order some, then why not using the one I suggest in the video?
@@BlueMoonshinethis ic is not available in my near shops. That's why i ask about your suggestion. I have some other opamp ic but some specs are not same with this ic.
I'm wasn't talking about the PCB. The schematics, or circuit diagrams, of each stage of the block diagram are shown and explained in details in the video. All you have to do is to place your components on the bread board and write them according to these diagrams.
@@BlueMoonshine you mentioned quad op amp TL084 in the components list. What is the purpose of it. In the circuit you made you used two TL084 and one LM386. The connections in the schematic you shared and components you used is different to the circuit you made. Please clarify
@@waleedsajidbaloch9523 Well, if you watched the tutorial, you can see that you need a total of 8 op-amps (if I remember well) for the circuit. There is nothing that prevents you from using 8 individual op-amps, but using integrated circuits that contains 4 op-amps in a single chip makes it easier. The values of the components are not unique. The tutorial explains clearly how to calculate and choose values that work, and I simply made a particular choice. Regarding the LM386, as is explained at the end of the video, it is if you want to choose the option of using a single battery and turn it into a symmetrical power supply. If you don't want to go for this option, there is nothing that prevents you from using two 9V batteries connected in series, with the ground at the center.
