iLoad Mini Application Note

The iLoad Mini is shipped with a cable that terminates in a male USB Mini-B 5-pin connector that plugs in to a Loadstar Sensors's DQ1000 family Frequency Converter interface. If you wish to use the iLoad Mini as a standalone frequency sensor, you may cut off the Mini-B connector and connect the four wires within the cable to your instrumentation. The table below identifies the color coding of the wires and the pin-out of the USB Mini-B connector.

Line USB Mini-B Connector Pin Color Description
5V Pin 1 Red Power Requirement: 5V +/- 5% at 5mA.
CTRL Pin 2 White When CTRL = High, FREQ = Cx
When CTRL = Low, FREQ = Cr
FREQ Pin 3 Green Frequency Output.
GND Pin 5 Black Ground

The CTRL line acts as a switch. The FREQ line outputs the Cx frequency when the CTRL line is High, and outputs the reference Cr frequency when the CTRL line is Low.

The measuring device should have a buffered output CTRL and a buffered input FREQ as shown in the above block diagram.

Cx is sensor frequency and it varies with load. Cr is reference frequency used for environmental compensation. K is a constant determined by Loadstar Sensors as part of our calibration.

Cc is called the Compensated Output as defined below:

Cc = 5E6 - [10*(Cx - K*Cr )]

The formula for measuring the load (in lbs) is:

Load = qA*Cc2 + qB*Cc + qC

With no load, calculate Load0 using the above formula. Put a known weight on the sensor and calculate Loadx. The actual weight is the difference between the 2 loads:

W = Loadx - Load0

Loadstar Sensors will provide the following constants for calibrated sensors:

Constant Description
K Environmental Compensation
qA Quadratic A.
qB Quadratic B.
qC Quadratic C.