Timeline for Op amp is not amplifying a 2 mV signal
Current License: CC BY-SA 4.0
24 events
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| Nov 10, 2021 at 3:09 | history | bumped | CommunityBot | This question has answers that may be good or bad; the system has marked it active so that they can be reviewed. | |
| Oct 10, 2021 at 23:08 | comment | added | Audioguru | All the single opamps shown in this thread are not biased and capacitor-coupled properly. If they are biased and properly coupled then the person having the ECG test would be an antenna that picks up all the 50Hz or 60Hz electrical hum all around him which would be amplified 101 times. | |
| Oct 10, 2021 at 21:05 | history | bumped | CommunityBot | This question has answers that may be good or bad; the system has marked it active so that they can be reviewed. | |
| Sep 6, 2021 at 23:27 | answer | added | Daniel Melendrez | timeline score: 0 | |
| Sep 6, 2021 at 21:56 | answer | added | arnisz | timeline score: 0 | |
| Sep 6, 2021 at 20:36 | comment | added | Scott Seidman | @MarkoBuršič -- just took a peek at Harden's one-op-amp ECG circuit, and a) it isn't the circuit presented here, and b) it's not great, but so long as it doesn't saturate, it should work so long as filtering is done in code, and there's no aliasing. It would be better with an anti-aliasing filter. So far as saturation, there's a lot less headroom than I like to use for robust design, but the circuit should work in many cases | |
| Sep 6, 2021 at 20:28 | answer | added | Scott Seidman | timeline score: 1 | |
| Sep 6, 2021 at 17:22 | answer | added | AnalogKid | timeline score: 0 | |
| Sep 6, 2021 at 17:17 | history | edited | Transistor | CC BY-SA 4.0 |
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| Sep 6, 2021 at 17:02 | answer | added | Stephan Neuhaus | timeline score: 0 | |
| Aug 28, 2021 at 8:47 | review | Close votes | |||
| Sep 7, 2021 at 3:02 | |||||
| Aug 28, 2021 at 3:18 | comment | added | qrk | Look for differential or instrumentation amplifier_ solutions. There are many web sites out there showing how to do an EKG instrumentation amplifier with three opamps. Then, look in to a notch filter at your AC line frequency (50Hz or 60Hz). | |
| Aug 27, 2021 at 22:56 | comment | added | D.A.S. | THat's a useless circuit amplifying 30 mVdc from skin voltage with an unbiased unbalanced differential input. DC coupled. 30mV *100 = 3V so the feedback R must be loose and is not biased in the Vcm range. Junk design | |
| Aug 27, 2021 at 22:24 | comment | added | Marko Buršič | It's a such a shame for Scott W Harden (swharden.com) that draws such circuits. Use Google to find another amplifier circuit, don't waste your time. | |
| Aug 27, 2021 at 21:23 | history | edited | Tom North | CC BY-SA 4.0 |
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| Aug 27, 2021 at 21:23 | comment | added | Tom North | @Audioguru I'm sorry I forgot to mention that the op amp is powered on a 9V battery | |
| Aug 27, 2021 at 21:15 | comment | added | Audioguru | The opamp is not powered then it does nothing. Depending on how it is powered then its + input is not biased at the correct DC voltage then it does nothing. It is missing a series input coupling capacitor then its input might be at its negative DC supply voltage so it rectifies the input signal. Of course the second "lead" must be connected to the signal ground and 0V of the power supply, not to the - input. Since the input level is low, shielded audio cable must be used at the input. | |
| Aug 27, 2021 at 21:10 | answer | added | John Birckhead | timeline score: 1 | |
| Aug 27, 2021 at 21:05 | comment | added | Voltage Spike♦ | If measuring an AC signal, it doesn't make sense to short it out on the terminals. | |
| Aug 27, 2021 at 20:53 | comment | added | DKNguyen | That circuit is wrong. I don't know why they have the right "lead" labelled where it is. That completely bypasses the rest of the circuitry and makes the op amp behave as an amplifier with infinite gain that cannot actually output infinite voltage so saturates at the power supply voltage whenever it does (i.e. that's what a comparator is). That right "lead" label should be at the same location as the ground. | |
| Aug 27, 2021 at 20:51 | comment | added | Tom North | @MarkoBuršič Well, shouldn't the op amp work like that? I'm very new to amplificator, I found about the formula that says V_s = V_e*(1+100k ohms/1k ohms) so it should amplify the signal to one that has an amplitude of 101*1mV = 101mV | |
| Aug 27, 2021 at 20:45 | comment | added | Marko Buršič | where did you get the idea that it should work like that? | |
| S Aug 27, 2021 at 20:32 | review | First questions | |||
| Aug 27, 2021 at 21:08 | |||||
| S Aug 27, 2021 at 20:32 | history | asked | Tom North | CC BY-SA 4.0 |