Custom Firmware, Electronics Design, and PCB Layout

Turn any Sensor into an SDI-12  Compliant Sensor

The SDI-12 Problem

Although SDI-12 is a cryptic hardware and software protocol, it is still a widely used standard interface between environmental sensors and data loggers.  Until now, sensor vendors have had the difficult and costly burden of creating their own SDI-12 solutions from scratch. Because of the many eccentricities of the SDI-12 protocol, it is a difficult task to create a truly compliant SDI-12 sensor interface.

The SDI-12 Sensor Engine

Figure 1 - SDI12 Sensor Engine Sample Board. 
(Productions boards are much smaller.)

Daycounter, Inc. has solved the problem of interfacing sensors to the SDI-12 bus by creating a small SDI12 Sensor Engine board which contains all of the necessary functionality. The SDI-12 Sensor Engine powers the sensor, and samples it with a high resolution ADC when it receives a measurement command from an SDI compliant data logger. The SDI-12 Sensor Engine handles all of the communication, and power down features of the SDI-12  protocol.  

Figure 2 shows a connection diagram for utilizing the SDI-12 Sensor Engine.  A single sided or differential output of the sensor is tied to the inputs of SDI-12 Sensor Engine. In addition the SDI12 Engine can sample One-Wire devices such as the Dallas DS18B20 temperature sensor.  The engine contains connection points for power, ground and the SDI-12 data line.  

Figure 2 - SDI12 Sensor Engine Connection Diagram.

Because of its small size the sensor can often be incorporated into the sensor housing.  Alternatively it can be used externally.  (The sample boards have terminal block connectors, so they are larger than production version boards. )  For sufficiently large quantities, we can provide custom board shapes to fit most any form factor.  

The Engine is extremely low power with only a 10uA current drain when it is sleeping, and it provides sensor power control, so that the sensor only receives power during a measurement cycle. 

All standard SDI-12 commands are supported. For large volume quantities, we can add extended commands for custom configuration of your application. 

Resistor jumpers control Voltage power levels to the sensor.  

How to Get Started with the SDI-12 Sensor Engine

The best way to try out the SDI-12 Sensor Engine is to order a few samples and connect them to your sensor.  The sample board contains a terminal block for quick connections.  Merely connect your sensor inputs to the SDI-12 Engine inputs, connect the Engine to your SDI compliant data logger, and start retrieving data from your sensor. Once your are satisfied that the SDI-12 Sensor Engine meets your specifications,  you can purchase the boards with a volume discount. 

SDI-12 Sensor Engine Samples (Quantity < 10)

$59.95 USD

Volume Pricing

 

Quantity (units)	Price Per Unit (USD)
10- 50	$49.95
51-250	$39.95
251-500	$34.95
501- 1000	$30.95
>1001	Contact us.

SDI-12 Sensor Engine Sample Specifications:

Sensor Protocol	SDI-12 Version 1.3
Power Supply Voltage	6V to 24V DC
Sleep Current	10uA
ADC resolution	16 bit, and 12 bit versions
Sensor Outputs:	Differential
	Single Sided
	One Wire Interface
Supported SDI commands	aM!, aMC!, aD!, aI!, aV!, ?!, a!

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