The gtdigital® Industrial Control and Monitoring Circuit Example
J. Bellott, MSEE
The Control and Monitoring Circuit (ICM) can perform a variety of functions, including:
· Smart Sensor – Record, analyze, and report measurements from attached sensors.
· Information Display - Display mode and status information on an LCD display with audio alerts and feedback.
· Remote Telemetry Unit - Send information to PC’s or other remote hosts via serial port.
· Remote Control of Connected Equipment – Via serial port
The ICM is useful for customers using lab equipment and process line equipment who need equipment to monitor or sense analog inputs and output digital signals, LED and Audio alerts, and messages via serial communications. Examples of equipment include pressure chambers, fluid bath thermal units, and other equipment.
The ICM can take readings from a wide variety of analog sensors through two analog input ports. Compatible sensors have voltage or resistive outputs that change depending upon the phenomenon being measured. Examples include:
· Temperature- Thermistors produce a voltage output that can be measured by the ICM.
· Pressure – Pressure transducers produce a signal that varies depending upon the force applied.
· Mechanical displacement – Mechanical displacement (or gap sizes) can be measured precisely by a gauge that uses a potentiometer whose resistance varies depending upon the position of the objects being measured by the gauge.
· Strain – Strain gauges are sometimes attached to metal by mechanical engineers to study stress and actual deformation levels of metal (strain). As the metal flexes, the attached gauge resistance changes. A common value is 200 ohms total, with +/- 50 ohms depending upon the amount of flexing of the gauge attached to a piece of metal.
· Luminance – Either presence or absence of light, significant changes in lighting levels, or other more precise readings can be taken using light sensitive sensors. Sensors can be calibrated using grey scale calibration filters (e.g. Tiffen filters) and a light source of known intensity. A typical CdS light sensor varies from 5 ohms to 600 ohms as brightness changes from dark to light. RGB colorimetry is also possible using precision color calibration filters with an appropriate light sensor device and light source.
· Other electrically compatible transducers.
The ICM includes a built-in Time of Day clock and thermistor for local ambient temperature readings.
The ICM uses a low cost, high performance hybrid DSP-Microcontroller from MicroChip, the world’s fifth largest microcontroller IC manufacturer. The 40 MIPS MicroChip dsPIC33 processor can perform blinding fast math and provides outstanding microcontroller performance.
The ICM uses a 20x2 character LCD module (4 digit LCD display optional in low power unit) to display operating modes, settings, and status. A four button interface can be used to navigate menus to adjust settings and to display status information. An optional keypad interface is built in which permits direct entry of digits while adjusting settings. The ICM audio circuit can provide audio feedback during user interface operation.
The ICM can be configured to work with sensors having a wide range of specifications. Both inputs can be scaled to adjust the input ranges to levels that are compatible with sensors being used.
Binary I/O interfaces can be used to control relays or to sense binary information from other digital circuits (e.g. sensing whether or not a cabinet door is open or an external switch has been thrown).
The ICM is powered by a 12 volt input. The unit can be mounted vertically on a wall or on the side of another piece of equipment. Sensors are typically in direct proximity of the ICM and can be connected using low resistance shielded cables.
The ICM features a serial port for communication with a remote processor. With custom firmware, the ICM can be operated remotely and can be used for remote digital telemetry, providing sensor readings with time of day information to PC’s at a centralized location in factories, process lines, or raw material storage areas. With custom firmware, the ICM can be used as a remote control panel for other pieces of equipment. It can also display status information from other equipment.
20x2 LCD Module Option, Keypad Option
Contact me about designing a similar control and monitoring circuit for your product line, authoring product development documentation, or user manuals for your manufactured product.