The circuit I posted was just a proof of concept simulation to try and provide some frequency compensation. A real-world circuit might need a fair bit of tweaking as the internals of the geophone are not fully known. You would almost certainly need an additional amplification stage. C1 should be a non-polarised type (or two polarised back-to-back).
But as Jon pints out, there's very little signal to amplify. Unwanted ambient noise could be a major issue to deal with.

 

hi,
If you are attempting to model a geophone in the real world on your project you could add them, but if you have the actual geophone, the answer is you do not need to add the components;
They have been created by Alec to mimic a real geophone. OK.?
E

Thanks. I just wasn't clear where the geophone ended and where the circuit started. I have the geophone, yep.

 

I think you're missing the key feature here. If I understand correctly, you want to see data down to 0.1Hz. You're out of gas. There's no signal to amplify at 0.1Hz. The slope of the response below 5.4Hz is 40dB/decade. At 0.1Hz, the response is about 50dB down (assuming the slope continues off the graph) - about 1/300 less response than at 5.4Hz.

View attachment 290236

I'm far from any kind of expert on this, but I was under the impression that is what a force balance circuit did - extended the capabilities of the geophone. This is done in the paper I linked to, and by raspberry shake, which also uses a force balanced bandwidth extended 4.5hz geophone. That is the goal anyway.

 

Good luck with that.

 

Good luck with that.

Thanks. That's why I'm here.

 

This was my initial attempt based on the paper. Worked good, just not as sensitive below 10hz as I hoped. Doing the new one now on a breadboard.

 

The circuit I posted was just a proof of concept simulation to try and provide some frequency compensation. A real-world circuit might need a fair bit of tweaking as the internals of the geophone are not fully known. You would almost certainly need an additional amplification stage. C1 should be a non-polarised type (or two polarised back-to-back).
But as Jon pints out, there's very little signal to amplify. Unwanted ambient noise could be a major issue to deal with.

Hi Alec,

So there is another amplification stage. The ADC has a built in amplifier that works well and goes up to 16 gain, and is programmable. That is what I was using to amplify what I had and it was working great between about 8 and 60hz. Just trying to push it farther down.

If I'm getting this right, you have built the same circuit that was in the paper I posted, I don't see any differences? All I need to do then to match your circuit is swap out R3 (I had 290K) and R4 (I had 10K) and the 0.1uF cap with a 100uF cap? So If I get this right you're setting the gain (1 + R4/R3) to 23.5? I have a bunch of resistors, but none that are 2700. As long as I hit gain close 23.5 can I use a different combination?

Gracias.

 

Hi Jon,
Read the link in post# 4, showing a method of extending the lower range response.
The author and his team have posted results indicating/claiming this is possible.
E

 

As long as I hit gain close 23.5 can I use a different combination?

Your choice entirely. The gain I used was arbitrary.

 

Your choice entirely. The gain I used was arbitrary.

Well, got it wired up. Getting signals fine, doesn't seem to be extending that 0-10hz sensitivity much though unfortunately. I think I wired it up correctly. Vertical stripes are cars driving by my house. Horizontal signal is a fan running.

 

An LM358 has a 1/f noise corner at about 60Hz. This is simply the wrong part to use in a sub 10Hz application, especially if additional gain is required below 4.5Hz.

Use a good zero-drift amp and very low tempco resistors. This will greatly increase the sensitivity of your geophone.

 

Use a good zero-drift amp and very low tempco resistors. This will greatly increase the sensitivity of your geophone.

Is this the correct way to wire that circuit up? The orange wires are the resistors.

Do you have an opamp you can recommend? I have a few on hand I ordered. LM324, LM358, LM386, LM393, UA741, NE5532, NE555, PC817, ULN2003, ULN2803?

Thanks

 

Is this the correct way to wire that circuit up? The orange wires are the resistors.

Do you have an opamp you can recommend? I have a few on hand I ordered. LM324, LM358, LM386, LM393, UA741, NE5532, NE555, PC817, ULN2003, ULN2803?

Thanks

I use LTC2050s. Aside from that, I've no comment as I haven't carefully read this thread.

Others will chime in.

 

Hi daveos,
Which circuit diagram did you use for the post #30 testing.?
The layout and pinning of the bread board circuit post #32, looks completely wrong.???
E

 

Hi daveos,
Which circuit diagram did you use for the post #30 testing.?
The layout and pinning of the bread board circuit post #32, looks completely wrong.???
E

That was supposed to be the layout from #15. Apparently I did not get it right. I see the opamps are backwards in the diagram. Updated here.

 

Morning daveos,
Which OPA have you decided to use on this project.?
E

 

Morning daveos,
Which OPA have you decided to use on this project.?
E

I updated the diagram in last picture, the opamps were backwards in the pic, or I mounted them backwards. They are the same ones in the paper, LM358.

 

hi,
This diagram shows the pin numbers, also the essential decoupling capacitors for the project/

The LM358 is a Dual OPA.


@daveos Redo the bread board layout using this circuit and pin numbers.

E

 

hi,
This diagram shows the pin numbers, also the essential decoupling capacitors for the project/

The LM358 is a Dual OPA.


@daveos Redo the bread board layout using this circuit and pin numbers.

E
View attachment 290572View attachment 290573

I'm very new to this. Does this look right using both sides of one opamp instead of two? The blue lines represent the resistors. Thanks

 

Hi daveos,
Sorry, but that poorly placed layout will cause you problems.
I will draw up a sketch and post later today.

E