DIY Instrumentation Amplifier using LM324N
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- Опубликовано: 23 июл 2024
- DIY Instrumentation Amplifier using LM324N
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Наука
The big cost in the off the shelf instrumentation amplifier is in the laser trimmed internal resistors. By trimming all those internal resistors to the same matched values common mode rejection ratio (CMRR) of over 120dB can be achieved. You should check the output of your circuit with both inputs shorted together. Ideally you will measure zero volts. Try then applying a common mode voltage of 1 volt and measure the output again and calculate the CMRR. You can and should match the 10k resistors to achieve close to similar CMRR as the expensive instrumentation opamp. Most board based instrumentation amplifiers have trimmer or a null multiturn potentiometer included in the design. Also instrumentation amplifier for high gain applications ( e.g. thermocouple amp) need very low drift opamps in the build.
You are right. But it won't help in this case. LM324 has huge input voltage offset so precise resistors would not help much...
Given the cost of 1% MF 1/4W resistors, I'd be tempted to buy a pack of 100+, then spend some time binning them. That way you know your CMRR will be good. Then maybe add a multiturn pot to trim the gain.
Using a Wheatstone bridge to match the resistors, and you could easily get it past the accuracy of common test equipment.
Dear Paul, I do like how you constantly stimulate our thinking with your projects.
Cool stuff Paul. I like the building blocks idea. Thanks for the video!
Did a bit of research: "In 1963, a 26-year-old engineer named Robert Widlar designed the first monolithic op-amp integrated circuit, the uA702, at Fairchild Semiconductor. It sold for US $300 a pop. Widlar followed up with an improved design, the uA709, cutting the cost to $70 and making the chip a huge commercial success" spectrum.ieee.org.
Although you can purchase an LM324 for less than a Snickers Bar (so good!), $11 for a precision op-amp is not too bad.
Thanks for the video Paul and have a great 4th!
Awesome vid, as always.
Thanks for sharing
Damn only $10.99 for two large pizzas?
Neato and great demonstration, happy 4th to you stay safe and cool!
That schematic looks like a spaceship, docking with the iss!
Very nice design and useful. Keep the faith and stay safe.
You forgot to factor in the $18 shipping in your cost.
Funny video.
The main thing about instrumentations amplifiers is the differential inputs (I guess it is what you called common mode rejection). They do not care about signal level and ground as long as the signal is within their operating range. For this to work well they need some precision resistors and that is what you get in the package: 3 OpAmps with laser trimmed precision resistors on the same substrate.
The circuit is very simple as you show, the issue is getting precision resistor that tracks over a wide temperature range and the laser trimming cost a lot of money.
When I first started learning about electronics, op amps caused my brain to just shut off! Thanks for the learnings! And Happy 4th! O'July
Great video!!
A great video, but I have a question as a newbie in electronics. Feeding 5v into the LM324, and on both pins 3 and 5 there is 0.3v approx, then on pin 8 there is 1.8v approx, which is quite a gain! Is this correct. Thanks
Awsome vid bud
Using lm 324 able to amplify the thermocouple signal in mV ??
hello nice video, where can i find the gerber files of the preamp you made?
WOULD YOU WIRE IT WITH A WHEATSTONE BRIDGE CIRCUIT TO MEASURE TEMPERATURE?
Hey Paul.
Believe it or not, I am actually building the exact circuit to amplify a pressure sensor. In my circuit, I am using the buffers to stop the differential amplifier resistors from dragging down the signal. That is, no gain on the buffers but rather on the differential amp. My question is this. Can you explain how the 'Gain resistor' can be common to both buffer amps without losing the integrity of the input signals?
Excellent
Paul that light blue PAD on your table where did you get it can you provide a link. Or is it in your store.
It's in the store
whats common mode rejection???
What circuit board builder/ generator do you use. It seems really nice. Would love to use it too for my projects.
Easy Eda
God Bless America! Happy 4th to you sir!
What if the input voltage in microvolts? I would like to use this concept to measure EEG/ECG impulse from human body
It's perfect for that
The INA114 is expensive, not something you have laying around just for fun but you do pay for precision.
Didn't you say "if you can't make it precis, make it adjustable"?
Didn't you forget that 😉
Good to know this circuit.
Bandwidth is an issue for these cheap operational amplifiers. The LM324 (I have 1K in stock) - it's bandwidth is good for about 5KHz if it is necessary to have minimal distortion (the difference between the input and the output signal) A quality class AB audio amplifier would have possibly 0.01 percent distortion, and have a bandwidth of possibly 20Hz to 20KHz (or hi fidelity)
Nice video keep up the great work 5☆
Hello, i wonder is this circuit usable to measure thermocouple heat sensor. And please make pcb making videos.
Yes
nice video. but lm324s totally make lamest and pretty unusable INA. manly because of the huge offset voltage they have.
That amp is good. But... TL081 /TL082 very low noise JFET input. Look into it. TL084 quad is only $0.47
You were outside...lol
If this was the reference INA, they would have dropped the entire idea a long time ago. It's so inferior to that, old otherwise INA114. For an INA, one actually buys the performance not the basic topology. The IC producers worked a lot to tune in the technology in order to get the datasheet performances. Were those 0.5W resistors, by the way? And no decoupling cap at all. Some scope's images would have shown it's lacking. The video is instructive but the INA you made, it's only an attempt of reaching the real thing.
@Rob C Nice channel, but a sense of realism helps getting a good picture. Some solutions can be improved if they are looked at with a critic eye. A hobby can get some people a long way through. I didn't think this was a knitting channel an Paul is indeed an engineer. Respectfully.
Dude I’d pay for classes from you ... you should make a videos on reading a schematic and what every symbol means.
Hello Paul. I'm curious why you didn't terminate the unused opamp? It would have been simple enough to implement on your PCB, and a good topic to teach. Happy 4th of July to all our American neighbors, from Canada!
There are many reasons why manufacturers do not base their instrumentation amps on an LM324. What you have built is probably “the world’s worst instrumentation amplifier” 😂
No way a normal OpAmp like LM324 can replace any Instrumentation OPAmp for various factors like offset trimmed, laser-trimmed register, near matching values, R2R input and R2R output and also high gain, which oscillation control. That's why they cost more but do the actual job. Your video is good for learner but not a complete one. Like it does not show the Zero output match, required double biased PS, the maximum V+ diff etc.
Also, when you can spend $22 just for simple PCB then when not $10 for Instrument OPAMP ?
why are you being so pedantic?.... just appreciate the help that Paul is giving for free.
Really interesting subject. Thanks. Too many adds though.
Struggling Artist ads
I put one ad at the beginning. Are you seeing more than that? If you are please email me arduino0169@gmail.com and tell me.
Kind of jaded, I mean it’s Independence Day weekend... I think it’s ok to show a tiny amount of patriotism at this point.
Just funny. I live in a tiny town. Never seen this guy before. Just made me laugh.
LM324 is one of the worst Op amps I have ever come across. They read between 0.2 and 0.6 volt difference between the input terminals. From there all gain calculations are out of the window.
photoresistor keplers laws galactic circuits, the sun amplifies its rays
Ummm....I would do check...putting both inputs at ground..to ensure that the output is at zero volts.
One note..ummmmm $ 5 for the PCBs and $ 18 for the shipping...This is only few grams...DHL and Fedex are really....scamming the customer on this tiny packages. This PCBway company should have a more cost effective shipping company!!!! There tons of products that we get from CHina...with free shipping...Something is not right between the product cost and the shipping.
You don't get free shipping from China in 5 days.
@@learnelectronics Correct...it takes 3 to 5 weeks. However, even Fedex takes two weeks...I don't see the point of using Fedex or DHL and paying about $ 20....since your product will take few weeks anyway. There is this malicious idea that PCBs are cheap to charge you more for the shipping. I hope this is not true and that the shipping cost is what it is from Fedex or DHL.
You can pick any shipping company you want.
@@learningpower9437 What is the cost of a jiffy bag and US postal rate? and how many days to arrive? Just curious.
brave walking with US flag these days xd
A bit too long.
Ya....it's working.....right.... I suppose that's why a 'true' 'instrumentation amp' costs so much....since it's precision.... NOT hacked together with a dirt cheap single-ended quad op-amp...and as some else said in the comments....at least you could have used matched resistors, or use 1% metal films.... I don't think you actually tested it in a 'common-mode' situation.... nice pcb though, even though the layout was amateurish .... if you're measuring tiny mVolt inputs, keep those inputs 'away' from power, etc.....just saying...