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MIMIC Wireless Remote Control for power and AC devices

To easily do Wireless Pump Control, AC light control, and many other remote control applications, Raveon has added a “MIMIC” mode to the M7 series of data radio modems. It works for not only wireless pump control, but also to remotely control most any electrical device that is turned on and off with a switch or relay.

The MIMIC mode allows two or more M7 data radio modems to “mimic” each other’s digital I/O.  When in the MIMIC mode, the M7 will periodically transmit its digital status.  The M7 will also continue to operate as a radio modem, sending/receiving data using pins 2&3 of the DB9, but the other I/O pins of the DB9 will be used for digital input/output. The MIMIC mode also has a fail-safe setting, so that in the event the radio link is broken, the receiving MIMIC radio will automatically set the MIMIC output to a pre-defined state.

Normally, the Serial I/O connector operates like an RS232 serial interface.  If the MIMIC mode is enabled, the operation of the radio is modified to transmit the digital status of the INPUT0 and INPUT1 pins across the radio link, and output their status on the OUT0 and OUT1 pins.

Optional MOSFET Driver

The M7 radio modem has an optional MOSFET output driver on the OUT0 output. (Only the OUT0,, not the OUT1 output).  If this option is installed, OUT0 will be pulled to ground to energize an external relay or lamp whenever OUT0 was supposed to go low.  So closing S1 on the sending station will cause OUT0 to go low, energizing the relay/lamp/led…

The MOSFET that drives OUT0 is a 2N7002 type device.  Do not connect a lamp/relay that draws more than 100mA to OUT0.  Also, if OUT0 is driving an inductive load, use a surge-protection diode such as a 1N4001 across the load to prevent high-voltage transients.

If the optional MOSFET driver is not installed, OUT0 will simply follow INPUT0 with RS232 signal levels.

MIMIC mode will work without the optional MOSFET, but if you want the M7 radio do drive one relay or medium-current device, then you must order the MOSFET option for OUT0 from the factory when the M7 is purchased.

MIMIC Hardware

There are two aspects to the MIMIC mode:

  1. The transmitter that sends the status of its digital inputs.  This is enabled with the MIMIC X Y command.
  2. The unit that receives the over-the-air MIMIC message, and sets its digital outputs to match the inputs of the sending station.  This function is enabled with the ATIO 1 command.  ATIO 1 configures the DB9 serial port to operate with RS232 signal levels, and use the digital control lines for digital I/O instead of RS232 flow control.  ATIO 0 turns off MIMIC reception ability, and the digital I/O pins will operate as flow control signals.

The goal of the MIMIC mode is quite simple: Flip a switch at one location, and have something at another location turn on or off.

Configuring an M7 for MIMIC mode

MIMIC transmissions are enabled with the MIMIC X Y command.   MIMIC 0 disables MIMIC mode and puts the unit in standard radio modem operation mode.  MIMIC X Y with X and Y being any positive number will enable the MIMIC feature. The MIMIC X Y command sets the unit to transmit a MIMIC over-the-air message every X seconds when INPUT0 is low, and to every Y seconds when INPUT0 is high.

For complete details on configuring an M7 for MIMIC mode, see application note AN161_MIMIC_M7.

MIMIC Command settings

If digital input INPUT0 is low, every X seconds, the M7 will automatically transmit the digital status of both the the INPUT0 and INPUT1 pins.  If INPUT0 is high, every Y seconds, the M7 will automatically transmit the digital status of the INPUT0 and INPUT1 pins. For example, MIMIC 2 60 configures the radio to send the state of INPUT0 and INPUT1 pins every 2 seconds if INPUT0 is low, and every minute if INPUT0 is high.

Radio addressing operates as it does in the standard mode.  When a unit receives a MIMIC transmission intended for its ID, it will set its OUT0 and OUT1 pins as determined by the sending stations INPUT 0 and INPUT1.

When the unit is in the Command mode, MIIC transmissions will not take place. The command mode is entered by sending +++ into the serial port.  See the M7 Technical Manual for information on how to configure the M7 using the built-in commands.

The MIMIC transmissions are the same over-the-air format as a standard data transmission from an M7 radio modem, except they contain no user-data, only digital I/O information.  An M7 radio modem configured as a repeater will repeat the MIMIC messages.

Failsafe Settings

To ensure failsafe operation, a FAILSAFE A B command sets the minimum message interval, and the default digital output state if an over-the-air MIMIC message is not received within the failsafe period.  A is the minimum period, and B is the ASCII hex value of the digital outputs if the failsafe interval passes and no MIMIC messages are receive.  B is also the power-on default value of the digital outputs.

For example, FAILSAFE 60 1 configures the unit to require a MIMIC message at least every minute. If one is not received within 60 seconds, OUT0 will go high (open drain), and OUT1 will go low (below ground).

It is recommended that the A value for the FAILSAFE command be about 2.5 times longer than the largest of the X and Y values of the MIMIC command.  This allows for one MIMIC message to be missed.  For example if MIMIC transmissions are set to MIMIC 2 60, a reasonable FAILSAFE A B setting would be a value of 150 for A. This will allow one MIMIC message to be missed and the FAILSAFE value not kick in. If more than two MIMIC messages did not get received, after 150 seconds, the M7 would revert to the failsafe values.

Filed under: Programming and Configuring, SCADA and Telemetry | Posted on November 2nd, 2010 by John Sonnenberg

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