Relay Board Control

The following components utilise the relay board:

• Refill Control: refilling of fresh water depending on water level
• Feeder Control: stopping flow pumps, skimmer and actuating the feeder
• Water Exchange Control: actuating the external pump for water exchange
• Balling Control: actuating the pumps for mineral dosing

There are two requirements, which ask for a more sophisticated control of the relay board:

• The dosing of minerals needs to be as precise as possible.
• The communication with the board needs to be reinitialised and even reopened after certain periods of time.

The relay board control implements the following features:

• Low level communication via serial port to the board
• Watchdog for reading/writing to serial port
• HW functionality test before executing commands
• Monitoring and repair of relay board states
• Avoiding conflicting access to relay board

Low level communication via serial port

This functionality is implemented in RlyBrdCtrl/RlyBrdCmd.c.

Watchdog for reading/writing to serial port

This functionality is implemented in RlyBrdCtrl/RlyBrdWtchDg.c.

HW functionality test

This functionality is implemented in RlyBrdCtrl/RlyBrdFdbck.c.

The control system connects a voltage input through one relay of each board to a GPIO pin of the Raspberry Pi.

By measuring the GPIO pin state, the control system can determine if the opening/closing of the relay really happened instead of just relying on the feedback of each board.

The feedback test evaluates three steps:

1. Starting with an open relay, check if GPIO state is FALSE
2. Closing the relay, check if GPIO state is TRUE
3. Opening the relay, check if GPIO state is FALSE

The feedback test executed before relay switching sequences (e.g. feeding pattern, Balling dosing, ...) and in regular time intervals (every 30min).

Monitoring and repair of relay board states

This functionality is implemented in RlyBrdCtrl/RlyBrdMidLay.c.

Avoiding conflicting access to relay board

This functionality is implemented in RlyBrdCtrl/RlyBrdHiLay.c.

Mutual exclusion is implemented using a semaphore (mutRlyBrdSchdlr).

The semaphore is used only by the function RlyBrdSchdlr. This function is the central gateway for all other components to initiate usage of the relay board. It shall give control of the relay board to a calling component so that the calling component can execute a sequence of commands which shall not be interrupted.

The function uses two callbacks which are provided via argument and a label informing which component is using the relay board:

RlyBrdSchdlr (int TestFunc(void), void ExecFunc(void), char *lbl)

The first callback function (TestFunc) allows the calling component to determine specifically which tests needs to be carried out before the relay board can be used. For example, the Balling dosing only needs to actuate the low voltage relay board while the feeder control only actuates the high voltage relay board.

In case the test function fails, there are two recovery strategies:

1. The communication with the relay board is reinitialised sending the related command. The test function is called again.
2. If the test function fails again, the serial device is reopened. The test function is called again.

The second callback function (ExecFunc) gives control to the calling component for execution of the sequence. Execution is only triggered if one call of the test function returned with a successful result.