V 1.4 Revised 4/21 Gravity ™ Analog Dissolved Oxygen Meter − + A Gravity DO Meter V2.0 Percent saturation only PATENT PROTECTED Written by Jordan Press Designed by Noah Press This is an evolving document, check back for updates.
Gravity dimensions 56.2mm (2.2”) − + A 24mm (0.9”) 32mm (1.2”) Gravity DO Meter V2.0 34mm (1.3”) 42mm (1.6”) Female SMA 22.3mm (0.8”) 11mm (0.4”) 6.2mm Ø (1/4”) 36UNS-2B Power consumption 5V = 0.3mA 3.3V = 0.3mA Absolute max ratings Parameter MIN TYP MAX Storage temperature -65 °C Operational temperature -40 °C 25 °C 50 °C VCC 3.3V 5V 5.
Operating principle The Gravity™ Analog class of meters offers the electrical engineer a low-cost solution to traditionally expensive measurements. This device gives the engineer access to the analog front end (AFE) of Atlas Scientifics Dissolved Oxygen sensing technology without the added cost that comes with complex mathematical processing. The Gravity™ Analog Dissolved Oxygen meter has been specially designed to read the voltage coming off a galvanic D.O.
Percent saturation A D.O. probe reads the partial pressure of oxygen. Using the percent saturation method, we can compare the partial pressure of oxygen in the atmosphere to the partial pressure of oxygen in the water and derive some information about its presence in the water. Because a dissolved oxygen probe can only read the partial pressure of oxygen, we are not able to determine the exact O2 content using this method. However, we can clearly determine its presence and partial pressure.
Converting the analog signal into percent saturation Every dissolved oxygen probe will output a slightly different voltage. Atlas Scientific's galvanic dissolved oxygen probe outputs ~40 – 60mV in air. = 42mV 58mV = This device can be used with a different brand of galvanic D.O. probe however, that probe may output a different voltage. The analog voltage coming off pin A is the voltage from the probe + an 11x gain. This means the analog voltage read on pin A is the voltage from the probe x11.
Connection pins Connect – to GND − + A Connect + to 3.3V or 5V Connect to analog pin / ADC Gravity DO Meter V2.0 Raspberry Pi 0 2 1 3 4 5 6 7 ICSP TX RX Arduino 0 1 8 9 1 L RX0 2 RX0 3 TX0 12 ) ON DIGITAL (PWM= ICSP2 TX0 TM 13 GND AREF Arduino Gravity DO Meter V2.0 L TX RESET RX ON TM − + A ICSP 1 A5 A4 A3 A2 A1 ANALOG IN A0 GND POWER VIN GND 3V3 5V RESET IOREF − AREF GND 13 12 11 10 9 8 I CSP PWM www. ar dui no.c c Ardui no MEGA www. ar dui no.
Electrical isolation The Atlas Scientific Gravity™ Analog Dissolved Oxygen Meter is a very sensitive device and is susceptible to electrical interference from external sources. This interference is caused by micro-voltages entering the water from unnatural sources such as pumps, solenoid valves, or other probes / sensors. When electrical interference is affecting the D.O. readings, it is common to see rapidly fluctuating readings or readings that are consistently off.
Sample code 0 1 3 ) RX0 4 5 6 7 8 9 10 11 12 13 DIGITAL (PWM= 2 ICSP2 TX0 RESET GND AREF Using the free downloadable arduino sample code, a one point calibration can be performed. The calibration procedure does not use any chemical buffer solution, instead you use the open air to calibrate your probe to 100% saturation. L TX RX Arduino ON TM A5 A4 A3 A2 A1 ANALOG IN A0 VIN GND POWER Gravity DO Meter V2.
