{"id":22120121,"url":"https://github.com/joshbrew/eeg-amplifier","last_synced_at":"2026-01-06T01:02:01.948Z","repository":{"id":195126858,"uuid":"692308706","full_name":"joshbrew/EEG-Amplifier","owner":"joshbrew","description":"Quad op amp differential amplifier with reference and gain stage.  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This should plug into any single ended ADC (or put your negative input to ground) to allow even as low as 10 bit EEG.\n\nThe amps cost 10 cents from TI, not including the PCB which will vary.\n\nThe reference design is for 1000x gain at 5v with a 2.5v voltage reference. All calculations are in the pdf for your needs.\n\n### Resources\n- [Differential Amp BOM](https://docs.google.com/spreadsheets/d/1rzFOKtwm5F1gYTblCt51H4664hxHK5iFGmpR6K0Omsg/edit?usp=sharing)\n- [Gain Amp BOM](https://docs.google.com/spreadsheets/d/1fu1xdZPcOAWwaKk6sFUOHw02OROvW1wCZvjth2xU8xA/edit?usp=sharing)\n- [Design reference](https://github.com/joshbrew/EEG-Amplifier/blob/main/EEG_Active_electrode_design.pdf) by Abishek Parikh. \nOther info pulled from datasheets.\n\nNote my previous OPA202 config was incorrect. And use this formula for calculating the bandpass: \n\u003ctable\u003e\n  \u003ctr\u003e\n    \u003ctd\u003e\n      \u003cimg width=\"200px\" src=\"https://github.com/user-attachments/assets/0b480666-d63d-422c-8c59-731e171d507b\"\u003e\u003cbr/\u003e\n      In our config, + is our reference \u003cbr/\u003e \n      (e.g. ear for EEG or opposite wrist for ECG)\n    \u003c/td\u003e\n    \u003ctd\u003e\n      \u003cimg width=\"200px\" src=\"https://github.com/user-attachments/assets/a81dac36-3ecf-41a9-b8cb-d12a59414333\"\u003e\n    \u003c/td\u003e\n    \u003ctd\u003e\n      Gain = R2 / R1\n    \u003c/td\u003e\n  \u003c/tr\u003e\n\u003c/table\u003e\n\n\n### OPA4202ID/TL084CDR/TL084OD (or compatible SOIC14) SMT mount.\n![amp2](./images/ampsmt.PNG)\nOPA4202ID is more expensive but MUCH better quality, with better input impedance (3TΩ) and a 9nV/sqrt(Hz) noise density starting at 0.1Hz. The TL084's spectral noise doesn't bottom out until near 1kHz.\n\n### 4mm Snap Button Electrode Mountholes\n![amp2mount](./images/ampsmtmounthole.PNG)\n![amp2mountCast](./images/ampsmtmountholecast.PNG)\nSized for Florida Instruments reusable plastic snap electrodes.\n\n### TL084HCN (A,B,H, etc) Thruhole amp (for DIY)\n![amp](./images/ampthroughole.PNG)\n\n### OPA4202IPW or OPA4377 (or  compatible TSSOP14) SMT mount.\n![amp3](./images/ampsmtOPA4377.PNG)\n\n### Schematics\n![schem](./images/schematic.PNG)\nThe BioAmp EXG Pill has a different layout you can check out. Same chipset.\n\n### Noise vs Measured Bandwidth on OPA4202\n![calcs](./images/noisecalc.PNG)\nNote: Noise calcs are probably inaccurate. Lower frequencies have higher noise density. Adjust bandpass accordingly.\n\nTL084 noise density:\n![density](./images/tl084noisedensity.PNG)\n\nOPA4202 noise density:\n![density2](./images/opax202noisedensity.PNG)\n\nOPA4202 or OPA4377 are about a dollar. I think the 4202 is better based on the noise.\n\n## Also included in CAD/singular_amps\n\nSingle and Dual OPA202/OPA2202 gain amplifiers. E.g. for pre-amplification. Great low frequency noise density. \n![gain](./images/InvertingAmp.PNG)\n\n\n### OPA202 (or pin compatible) VSSOP8 package (or pin compatible)\n![smtgain](./images/singleamp_SMTr2.PNG)\n\n### OPA202 VSSOP8 package with 4mm electrode mount\n![smtgain2](./images/singleampSMTMountr2.PNG)\n\n### OPA202 SOIC8 package and thruhole resistors/capacitors (easier to hand solder)\n![smtgain3](./images/singleampThrur2.PNG)\n\n### OPA202 SOIC8 package thruhole with 4mm electrode mount\n![smtgain4](./images/singleampThruholeMountr2.PNG)\n\nEAGLE drawings by Josh Brewster. Works in free EAGLE or you can import them elsewhere usually.\n\nBest prices are on TI.com just FYI...\n\nFree source! Definitely question my circuitry before you use it.\n","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fjoshbrew%2Feeg-amplifier","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fjoshbrew%2Feeg-amplifier","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fjoshbrew%2Feeg-amplifier/lists"}