scpi-multimeter

Open source hardware-independent single-channel SCPI multimeter.

Library Content

• implementation of basic SCPI multimeter commands, such as CONFigure, SENSe and other;
• measurement state machine implementing MEASure, INIT, FETCh and relating commands.

Library Features

• support of voltage, current and resistance measurements;
• support of asynchronous measurements: measure values may come from another thread or an interrupt handler;
• support of immediate, bus and external triggers.

Steps to Implement a Multimeter Using SCPIMM Library

Step 1

Implement callback functions providing access to measurement hardware.

For example, code below illustrates a set_mode callback function that switches our hardware to desired mode:

scpimm_error_t set_mode_callback(scpimm_mode_t mode, const scpimm_mode_params_t* params) {
  if (SCPIMM_MODE_DCV == mode) {
	/* switch hardware to DC voltage mode */
  } else if (SCPIMM_MODE_ACV == mode) {
	/* switch hardware to AC voltage mode */
  } else {
	/* requested mode is not supported by hardware */
	return SCPIMM_ERROR_UNDEFINED_HEADER;
  }
  return SCPIMM_ERROR_OK;
}

Step 2

Implement serial port access callback:

size_t send_callback(const uint8_t* data, size_t len) {
  /* send data to serial port or another destination */
}

Step 3

Populate scpimm_interface_t structure that holds pointers to all callbacks used by library.

Step 4

Initialize library with filled scpimm_interface_t structure.

Step 5

Run a loop that reads incoming data from serial port (or another source of data) and passes these data to library.

Example

Here is a sample code illustrating usage of the library. Library declarations start with either SCPIMM_ or scpimm_ prefix.

/* fill the structure with callback pointers */
scpimm_interface_t interface = {
  .setup = setup_callback,
  .set_mode = set_mode_callback,
  .get_mode = get_mode_callback,
  .send = send_callback,
  ... /* other callbacks */
};

/* initialize SCPIMM library */
SCPIMM_setup(&interface);

/* main loop */
while ( !is_terminated() ) {
  if ( data_arrived_from_serial_port() ) {
    const char p = read_char_from_serial_port();
    /* parse incoming data */
    SCPIMM_parse_in_buffer(&p, 1);
  } else {
    /* run background tasks */
    SCPIMM_yield();
  }
}

Library Dependencies

• scpi-parser - generic SCPI parser.

Library Usages

• v7-28-arduino - firmware for Arduino Mega implementing a SCPI multimeter backed by V7-28 digital voltmeter. This project can be treated as a reference usage of SCPIMM library.