Set a new standard for multifunctional testing with MCP3204 and PIC18F97J60
Explore our multimeter's versatile measurement capabilities
Published 9月 29, 2023
Click board™
Multimeter Click
Dev Board
UNI-DS v8
Compiler
NECTO Studio
MCU
PIC18F97J60
Experience a new level of convenience and accuracy with our comprehensive multimeter technology that offers unmatched versatility and precision in measuring voltage, current, resistance, and capacitance
A
A
Hardware Overview
How does it work?
Multimeter Click is managed by several different ICs, including operational amplifiers, NE555 timer, BCD decoder, frequency to voltage converter, and finally an A/D converter (ADC). The auxiliary ICs for providing -5V and the ADC referent voltage of 2.048V, are also present. The Click board™ uses the MCP3204, a four-channel, 12-bit ADC with an SPI interface, from Microchip. The conditioned signals are routed to each input of the ADC. The input channel is selected by the initial SPI command, after the #CS (chip select) pin becomes LOW. Three configuration LSBs are used to set the sampling channel (D0-D2), while the fourth bit (D3) sets the mode. The ADC is routed to work with single-ended inputs, and therefore this bit should always be set as 1. A differential input amplifier is used to amplify the voltage difference across the shunt resistor. One half of the MCP607, a dual CMOS op-amp from Microchip is used for that purpose. The value of the shunt resistor is 0.1Ω, which allows up to 1A of current to be measured. Since the ammeter is connected in series, the shunt resistor has to be of a very small value, in order to prevent interferences with the measuring circuitry. This is one of the basic requirements of the ammeter. The voltage drop at the shunt is amplified by the differential op-amp (by the factor of 10), and the op-amp output is routed to one of the ADC inputs, which is labeled I on the schematic. The op-amp uses half of the referent voltage (Vref) as the virtual GND so that both positive and negative values can be converted. When measuring a voltage, the internal
resistance of the voltmeter has to be large, since it is connected in parallel with the component across which the voltage is measured. The Click board™ uses the MCP609, a quad CMOS op-amp, configured as dual-buffer and a differential amplifier. It is the same device as the MCP607, but with four integrated op-amps. Two integrated op-amps work as buffers with voltage dividers at their non-inverting inputs, while the third op-amp acts as the actual differential amplifier. Again, the op-amp uses the virtual GND, set at half of the Vref for the output biasing. This allows both negative and positive voltage potential to be measured, across the load connected at the input terminal. The output from the differential amplifier is routed to the ADC input labeled as U. Measurement of the resistance consists of a voltage divider, which is formed by an unknown resistance connected to the resistance measuring terminal, and a selectable, known, reference value resistor. The voltage applied to the voltage divider is also known (Vref). The middle tap of the divider is routed directly to the ADC input pin labeled as R, allowing reading of the voltage which directly depends on the unknown resistance. The CD4028B, a BCD decoder IC from Texas Instruments is used to select the correct reference resistance range. Three input pins (A, B, C) of the CD4028B are used to activate one of 6 MOSFET gates, via the logic states of the AN, PWM and INT pins of the mikroBUS™, which connect the desired reference resistor to the measuring circuit. The capacitance property can be measured with
many multimeters commercially available, but it is not something included in some cheaper models. It consists of the NE555 precision timer, configured as an astable multivibrator. It generates impulses, set to about 50% duty cycle, with the frequency of 585Hz. This signal is converted by the LM2907MX, a frequency to voltage converter from Texas Instruments. The unknown capacitance is connected to the threshold input of the NE555, affecting the frequency of the pulses. The LM2907MX responds by changing the output voltage, fed to a differential op-amp. The higher the connected capacitance, the lower the LM2907 output becomes. The DC signal is then passed through another differential amplifier and routed to the ADC input labeled as CU, so it can be sampled by the ADC and read via the SPI. A software (or a firmware) running on the host MCU is required, in order to transform raw ADC readings and show them on an output device. The library provided with the Multimeter click offers a set of functions, which output straight-forward measurements and can be implemented easily in a custom code. Before actual measurement, as a part of the device initialization procedure, a calibration routine needs to be performed, so that components tolerances are taken into an account. Therefore, there should be nothing connected at the input terminals of the Multimeter click, until it is initialized by the software. The provided example application demonstrates how to use this click board, so it can be used as a starting point for future development.
Features overview
Development board
UNI-DS v8 is a development board specially designed for the needs of rapid development of embedded applications. It supports a wide range of microcontrollers, such as different STM32, Kinetis, TIVA, CEC, MSP, PIC, dsPIC, PIC32, and AVR MCUs regardless of their number of pins, and a broad set of unique functions, such as the first-ever embedded debugger/programmer over WiFi. The development board is well organized and designed so that the end-user has all the necessary elements, such as switches, buttons, indicators, connectors, and others, in one place. Thanks to innovative manufacturing technology, UNI-DS v8 provides a fluid and immersive working experience, allowing access anywhere and under any
circumstances at any time. Each part of the UNI-DS v8 development board contains the components necessary for the most efficient operation of the same board. An advanced integrated CODEGRIP programmer/debugger module offers many valuable programming/debugging options, including support for JTAG, SWD, and SWO Trace (Single Wire Output)), and seamless integration with the Mikroe software environment. Besides, it also includes a clean and regulated power supply module for the development board. It can use a wide range of external power sources, including a battery, an external 12V power supply, and a power source via the USB Type-C (USB-C) connector. Communication options such as USB-UART, USB
HOST/DEVICE, CAN (on the MCU card, if supported), and Ethernet is also included. In addition, it also has the well-established mikroBUS™ standard, a standardized socket for the MCU card (SiBRAIN standard), and two display options for the TFT board line of products and character-based LCD. UNI-DS v8 is an integral part of the Mikroe ecosystem for rapid development. Natively supported by Mikroe software tools, it covers many aspects of prototyping and development thanks to a considerable number of different Click boards™ (over a thousand boards), the number of which is growing every day.
Microcontroller Overview
MCU Card / MCU
Type
8th Generation
Architecture
PIC
MCU Memory (KB)
128
Silicon Vendor
Microchip
Pin count
100
RAM (Bytes)
3808
Used MCU Pins
mikroBUS™ mapper
Take a closer look
Schematic
Step by step
Project assembly
Start by selecting your development board and Click board™. Begin with the UNI-DS v8 as your development board.
Track your results in real time
Application Output
After pressing the "FLASH" button on the left-side panel, it is necessary to open the UART terminal to display the achieved results. By clicking on the Tools icon in the right-hand panel, multiple different functions are displayed, among which is the UART Terminal. Click on the offered "UART Terminal" icon.
Once the UART terminal is opened, the window takes on a new form. At the top of the tab are two buttons, one for adjusting the parameters of the UART terminal and the other for connecting the UART terminal. The tab's lower part is reserved for displaying the achieved results. Before connecting, the terminal has a Disconnected status, indicating that the terminal is not yet active. Before connecting, it is necessary to check the set parameters of the UART terminal. Click on the "OPTIONS" button.
In the newly opened UART Terminal Options field, we check if the terminal settings are correct, such as the set port and the Baud rate of UART communication. If the data is not displayed properly, it is possible that the Baud rate value is not set correctly and needs to be adjusted to 115200. If all the parameters are set correctly, click on "CONFIGURE".
The next step is to click on the "CONNECT" button, after which the terminal status changes from Disconnected to Connected in green, and the data is displayed in the Received data field.
Software Support
Library Description
This library contains API for Multimeter Click driver.
Key functions:
multimeter_read_resistance- This function reads and returns resistance datamultimeter_read_voltage- This function reads and returns voltage datamultimeter_read_voltage- This function reads and returns current data.
Open Source
Code example
This example can be found in NECTO Studio. Feel free to download the code, or you can copy the code below.
/*!
* \file
* \brief Multimeter Click example
*
* # Description
* This example showcases how to configure, initialize and use the Multimeter click. The
* click measures resistance in Ohms, voltage in mVs, current in mAs and capacitance in nFs
* using a dual CMOS and quad CMOS op-amps, an ADC and other on board modules.
*
* The demo application is composed of two sections :
*
* ## Application Init
* This function initializes and configures the logger and click modules. Additional
* calibration of the measurement components is done in the default_cfg(...) function.
*
* ## Application Task
* This function measures and displays resistance, voltage, current and capacitance data.
* It does so every second.
*
* \author MikroE Team
*
*/
// ------------------------------------------------------------------- INCLUDES
#include "board.h"
#include "log.h"
#include "multimeter.h"
// ------------------------------------------------------------------ VARIABLES
static multimeter_t multimeter;
static log_t logger;
// ------------------------------------------------------ APPLICATION FUNCTIONS
void application_init ( )
{
log_cfg_t log_cfg;
multimeter_cfg_t cfg;
/**
* Logger initialization.
* Default baud rate: 115200
* Default log level: LOG_LEVEL_DEBUG
* @note If USB_UART_RX and USB_UART_TX
* are defined as HAL_PIN_NC, you will
* need to define them manually for log to work.
* See @b LOG_MAP_USB_UART macro definition for detailed explanation.
*/
LOG_MAP_USB_UART( log_cfg );
log_init( &logger, &log_cfg );
log_info( &logger, "---- Application Init ----" );
// Click initialization.
multimeter_cfg_setup( &cfg );
MULTIMETER_MAP_MIKROBUS( cfg, MIKROBUS_1 );
multimeter_init( &multimeter, &cfg );
multimeter_default_cfg( &multimeter );
}
void application_task ( )
{
float resistance;
float voltage;
float current;
float capacitance;
resistance = multimeter_read_resistance( &multimeter );
log_printf( &logger, " * Resistance: %.3f Ohms * \r\n", resistance );
voltage = multimeter_read_voltage( &multimeter );
log_printf( &logger, " * Voltage: %.3f mV * \r\n", voltage );
current = multimeter_read_current( &multimeter );
log_printf( &logger, " * Current: %.3f mA * \r\n", current );
capacitance = multimeter_read_capacitance( &multimeter );
log_printf( &logger, " * Capacitance: %.3f nF * \r\n", capacitance );
log_printf( &logger, "------------------------\r\n" );
Delay_1sec( );
}
void main ( )
{
application_init( );
for ( ; ; )
{
application_task( );
}
}
// ------------------------------------------------------------------------ END
