Anyone had tried this? What are the things should I be considering or be aware of when doing this? I asked about connecting to the ESP32 directly and they said it should read the analog inputs but for smaller signals it can’t. I’m trying to use ADS1115 to connect to a Geophone then to the ESP32.
What is the make and model of geophone that you are using? It sounds like you are trying to measure a very small analog signal which should not be difficult provided you use a suitable amplifier. But the starting point is the specifications for the output from the geophone.
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Hi @Allen302188, welcome to the forum.
@Jeff105671 is right, we would need the specifications before forum members would be able to provide more detailed feedback.
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LGT-SM24 Geophone
I’m using Type C ESP32 With Wifi module 38 pins. I’ve asked if I can directly connect to the pins and they said it should read but not for smaller signals.
The LGT-SM24 Geophone will provide a very low voltage output at low impedance, but it may be usable if configured properly. There is mention of a shunt resistor which is presumably recommended. The device should be connected using the ADS1115 in differential mode (ie neither input connected to ground). You should set the ADS1115 amplification (PGA) to successively lower values until you get readings that are usable, but be careful that the differential does not exceed the PGA voltage setting or the supply voltage. You can calculate the expected voltage across the shunt using the sensitivity figure (eg 0.209V for a 1K shunt) and your expected cm/s movement to predict the likely voltage levels.
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Which pins should I use for this?
How do I set the PGA? I’m new to using ADS1115. I only have rought idea of how the pins work.
Let me interate again, if I want to detect signals as small as V*cm/sec, I need to set the PGA into a succesive value enough to detect that voltage?
Lastly, which pins should I use to create that differential volts coming in?
Thanks a lot for help!
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The manual shows the connections on P17:
Differential measurements use a pair of input pins, either A0&A1 or A2&A3. The following diagram shows connections for differential measurement of the battery voltage on a LiPo charger board
The device also supports A1&A3 together with A2&A3 but that is a specialised usage that doesn’t apply for your case.
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It’s a function available in the library.
void setGain(uint8_t gain);
The value to be used for gain (000b~111b) are set out on P26 of the datasheet.
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I can’t see the diagram, where can I find it
What libraries can I use for processing Geophone analog signal?
I’ve thought of following this schematics from a youtube video I watched
Is this schematic would be the same if I used an ESP board?
It’s P17 of the user manual.
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I’m not aware of any library specifically for processing the geophone data. I suspect that any processing would be very project specific. For instance, a project to identify resonant frequencies would make use of FFT: two that I have used with Arduino and will presumably work with ESP32 are arduinoFFT and ESPFFT . There are libraries available that will plot the signal (or just use the Arduino IDE).
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An ESP board will be very different than a Pi. However the interface to the ADS1115 is standard I2C, so any diagram that shows the I2C connections for your particular ESP module will work. You don’t need ALRT and ADDR can be allowed to float. The interface from the ADS1115 to the Geophone includes the 1K shunt and adds two resistors in series to increase the impedance, which looks sensible to me.
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why would we increase impedance if we want to read small signals?
I learned so much… Thanks alot!
You need sufficient impedance in the shunt to be able to read a voltage drop across it. The impedance needed in leads between the sensor and the terminals depends on the voltage you expect to be generating in the coil, and that in turn depends on the amount and rate of movement you are expecting.
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