Joshy said:
Oh, my suggestion wont work if you're trying to decrease the capacitance :( I think the earlier suggestions sound better you might want to consider those instead.
I recommend you share the application or maybe some of the schematic, or both. It might help with suggestions.
Please look at this schematic of the Olimex-EKG-EMG. I actually saw a web site how to modify it to increase the high frequency cut off from 40 Hz to 500 Hz (see below too). In my case. I want to increase the cut off to at least 1000 Hz.
https://www.olimex.com/Products/Duino/Shields/SHIELD-EKG-EMG/open-source-hardware
schematic of the product
https://www.olimex.com/Products/Dui.../resources/SHIELD-EKG-EMG-REV-B-SCHEMATIC.pdf
How to modify the Olimex from 40 Hz to 500 Hz.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9143621/
I saw the following product from UFI (Biopotential 2122) with high frequency cut off of at least 1000 Hz (and higher but I need only 1000 Hz for now). But they are selling it to me for $1200.
https://www.ufiservingscience.com/datasheets/2122manual.pdf
If the capacitors in the Olimex is modified to 1000 Hz. Can it matches UFI Bioamplifier 2122 performance? Kindly study the Olimex schematics and comment if the components have the the best design also possibly matching even very high end unit or it is not up to it.
For this UFI 2122 description "Introduction The Model 2122 is a differential amplifier for use with low level signals -- 2 microvolts and above -- ranging from DC to 10 KHz. Primarily designed as biological instrumentation, the Model 2122 is well suited to many other demanding applications. It features high common mode rejection, high input impedance, low noise, small size, and excellent frequency response. The Model 2122i includes subject isolation, but is otherwise identical to the standard Model 2122."
".... Less than 2 μV peak to-peak, DC to 100 Hz with 10K Ohm source".
Can the Olimex also has 2 μV peak to-peak, DC to 100 Hz with 10K Ohm source noise? Is this a common specification of typical amplifier these days and can easily be achieved? What happens if the frequency is increased to 1000 Hz, what usually is the peak to peak noise in microvolt? (Have you encountered or heard)?
Some disclaimers:
I'm not newbie in bioamplifiers (I owned 5 EEG units and my simulators in my biology research lab), so please don't keep emphasizing plugging it to AC can electrocute me and stop this thread right away. I'd never plug it to AC. I used isolator. And in the Olimex, it's connected with laptop with battery only. Never the AC plugged in. To all users too. Always use isolator to prevent turning it into electric chair or just don't do any project like this unless you know what you are doing.
2nd. Don't convince me that there is nothing to see in the EMG at 1000 Hz. I'm not building an EMG which has limit only of 500 Hz. I'm getting a Biopotential amplifier with cut off of 1000 Hz to prove to myself the body plexuses or nerve centers can't emit high frequency that can be measured in surface mount biopotential sensors. Yes. This may sound ridiculous but as biologist, I need to prove it so kindly dont tell me not to get the circuit and just believe. Also No. I'd never use needle. It's all surface measurement of the biopotential so worry not about sticking needles and hurting the body. I 100% will not use needles.
3rd. Can you recommend other biopotential amplifier that has very good quality at 1000 Hz and can detect even very small EMG-like level (1 microVolt and so) signal at low noise and high common mode rejection with same or better quality that the UFI Biopotential 2122 ? I just need 1 channel. It's alternative to the UFI Biopotential 2122 which is selling me at $1200. Problem with it is they only accept credit cards and wire transfer. So since I don't want to share my credit card. I have to wire transfer but it is more hassled. If I can find something with same quality at it and pay online, then it is much more convenient.
Thank you so much guys!