Seisberry configuration notes¶

Revision 2020-04-16

The goal is to build a 3 component seismograph (seismometer) based on a Raspberry Pi, an Analog to Digital Hat and 3 coil geophones.

The projects had to comply with the following technical requirments:

• 24 bit sampling for high dynamic and so gain setting is not critical in most applications.
• capable of a sampling rate of 1,000 Hz or faster (1ms sample Interval).
• Jitter at 1,000Hz inferior to 5%.
• 4 channels to operate with 3 geophones + 1 hydrophone (for a possible Ocean Bottom Node like use case, for very shallow water use).
• Output to Segy and Miniseed format for respectivly industrial and research purpose.
• price tag under 100 USD for a single component mode and under 150 USD for a 3 component land node, to be relevant to the education community and to be accessible in developping countries.
• All software opensource and 100% available to the community (Github).
• Possibility to operate the node in the field as a mobile unit, with the clock synchronized to GPS time.
• Possibility to operate the node as a permanent station, fully autonomous, and automatically uploading its data to a DMC remote server (Iris).
• One click access to daily recorded data, when the node is connected to a network, with results displayed on a dynamic web page hosted on the node.

The first 4 requirements insure the node performs as well (or better) than most system available in the industry in 2020.

Parts needed¶

• Raspberry Pi 3 B+: USD 35 (Raspberry Pi 4 has a higher power consumption and possible compatibility issue with the ADDA board):
• Onboard ADS1256, 8 channels 24 bit high-precision ADC (4ch differential input), 30ksps sampling rate: USD 29
• 3 geophones (1 vertical, 2 horizontal), with their shunt resistance. I use: RTC-10Hz 395 Ohms with 1000 Ohms shunt: USD 30×3.
• wires and a box.

Raspberry Pi OS install:¶

It is strongly suggested to use a Raspian OS as many useful libraries for Raspberry PI come pre-installed. Use the full install, with desktop and the various Pi libraries.

Download Raspian Buster (2020) image, check SHA 256 hash. With Balena Etcher, flash the SD card with the Raspian Buster image. Connect a screen, mouse and keyboard to the Pi. Boot the Raspberry with the image out of Etcher. Configure password (use a strong password as we will be opening SSH, VSP etc..) then the hostname to “seisberry”. Update the distribution (just follow the wizard that should pop up automatically after the first install). Configure wifi, keyboard, date. Allow VSP and SSH connect in Preference > Raspberry Pi Configuration. Do ifconfig in a terminal and write down the node’s IP on the local network. Example IPv4 is: 192.168.1.118 Power down.

Connect the High-Precision AD-DA Board to the Raspberry Pi, via the GPIO header.

Jumper settings: Set the Power Supply to 5V: connect the pin 5V and VCC. Set the Reference Input Voltage to 5V: connect the pin 5V and VREF.

For testing the board only: Set the Potentiometer output as an Analog Input: connect the pin ADJ and AD0. Make sure the left side Sensor Interface AD0 is disconnected. Set the LDR (Light Detection Resistor) output as an Analog Input: connect the pin LDR and AD1. Make sure the left side Sensor Interface AD1 is disconnected. Last connect AINCOM to AGND, to set the board to single handed (as opposed to differential).

Note: later, when using AD for differential measurements (which is what we will do for the geophone application), INCOM and AGND need to be disconnected, ie the jumper removed. Of couse LDR and Potentiometer will also be disconnected.

Power up the Raspberry Pi with the HAT now connected. Both the HAT and the Pi should have their power led on. VNC to seisberry (I use VNC viewer, free). If your local DNS is setup right, “seisberry” is the address, alternativly use the IP previously noted. If you do not want to VNC, connect a screen, mouse and keyboard to the Pi.

The doc on sharewave (https://www.waveshare.com/wiki/High-Precision_AD/DA_Board) is out of date, applies for older versions for which the files are unavailable. Do not follow it, follow this tutorial instead:

A powerful feature of the Raspberry Pi is the row of GPIO (general-purpose input/output) pins along the top edge of the board. A 40-pin GPIO header is found on all current Raspberry Pi boards. Any of the GPIO pins can be designated (in software) as an input or output pin and used for a wide range of purposes. Your High-Precision AD-DA Board is connected to the Pi’s GPIO bus.

WiringPi is a C library used by C programs for GPIO connections. RPi.GPIO is a Python library used by Python programs for GPIO connections.

Both libraries are PRE-INSTALLED with standard Raspbian systems! You do not need to install anything. Disregard the High-Precision AD-DA Board manual.

Optional step: you can check your GPIO libraries versions: