Multimeter click
PID: MIKROE-3116 Weight: 29 g
Multimeter click is a Click board™ designed to measure voltage, current, resistance, and
capacitance properties of the components, connected to the input terminals. Each property
measurement is done on a separate terminal. Each measurement section conditions the input
signal from the respective input terminal and forwards it to a four-channel 12-bit A/D converter.
All the inputs are equipped with the differential amplifiers, that allow both positive and negative
signals to be measured. By utilizing the binary-to-decimal converter IC, it is possible to select
the optimal range for the resistance measurement. Low internal resistance of only 0.1Ω for the
current and high resistance of 1MΩ for the voltage measurement section, ensure no
interferences with the measured circuitry, caused by this Click board™.
Since there are four distinctive properties that can be measured with Multimeter click
which all require different measuring techniques, several different ICs had to be used on
the Click board™. Starting with the high-quality, low noise A/D converter as the primary
component, all the way to the input operational amplifiers, all components were hand-
picked to ensure accuracy. Even the lowest amounts of noise, distortion, or crosstalk,
might have a great impact on the overall accuracy of the measurement. This Click
board™ can be used as the development platform for measurement applications, or
simply as a very compact, accurate, and handy digital multimeter device.
How does it work?
The operation of this Click board™ 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 fourchannel, 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.
Current measurement
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.
Voltage measurement
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.
Resistance measurement
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.
Capacitance measurement
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, which is 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 DC output
voltage, which is 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.
Software
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 (UART, display...) 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.
Specifications
Type
Measurements
Applications
This Click board™ can be used as the development platform for
measurement applications, or simply as a very compact,
accurate, and handy digital multimeter device
On-board
modules
MCP607 dual CMOS op-amp, MCP609 quad CMOS op-amp,
MCP3024 12-bit ADC, by Microchip; NE555 timer, CD4028 BCD
decoder, LM2907 freq to voltage, by Texas Instruments;
MAX6106 2.048 V reference, by Maxim Integrated
Key Features
Low internal resistance for the current and high internal
resistance for the voltage, five different resistance measuring
ranges, capacitance measurement, separate inputs for each
measured property
Interface
GPIO,SPI
Input
Voltage
5V
Click board
size
L (57.15 x 25.4 mm)
Pinout diagram
This table shows how the pinout on Driver click corresponds to the pinout on
the mikroBUS™ socket (the latter shown in the two middle columns).
Notes
Pin
Range Sel Bit 0
A
1
AN
PWM
NC
2
RST
CS
3
SPI Clock
SCK
SPI Data OUT
SPI Data IN
SPI Chip Select
Pin
Notes
16
B
Range Sel Bit 1
INT
15
C
Range Sel Bit 2
CS
RX
14
NC
4
SCK
TX
13
NC
SDO
5
MISO
SCL
12
NC
SDI
6
MOSI
SDA
11
NC
NC
7
3.3V
5V
10
5V
GND
8
GND
GND
9
GND
Power supply
Ground
Ground
Onboard jumpers and settings
Label
Name
Default
Description
LD1
PWR
-
Power LED indicator
V meter
Voltmeter symbol
-
Voltage measurement input
terminal
A meter
Ammeter symbol
-
Current measurement input terminal
R meter
Resistor symbol
-
Resistance measurement input
terminal
CU
meter
Capacitor symbol
-
Capacitance measurement input
terminal
Multimeter click electrical specifications
Description
Min
Type
Max
Unit
-
5e‐4
-
V/bit
Current measurement range
0.001
-
1.024
A
Voltage measurement range
0.008
-
17.068
V
0.25
-
20M
Ω
0.001
-
2.2
µF
Measurement resolution
Resistance measurement range
Capacitance measurement range
Software support
We provide a library for the Multimeter Click on our LibStock page, as well
as a demo application (example), developed using MikroElektronika
compilers. The demo can run on all the main MikroElektronika development
boards.
Library Description
The library contains calibration function, to be used on startup for more
accurate readings, as well as
4 functions that measure Voltage, Current, Resistance, and Capacitance.
Key functions:
float multim_measure() - 4 functions for measuring Voltage, Current, Resistance and
Capacitance.
void multim_calibrate() - Calibration function that needs to be called on startup.
Example description
The application is composed of three sections:
The application is composed of three sections :
System Initialization - Initializes pin control, SPI peripheral and logger.
Application Initialization - Initializes the driver, and performs calibration. Application Task (Code
snippet) - Outputs read values.
char text[20];
float value = 0;
value = multim_measureR();
FloatToStr(value,text);
mikrobus_logWrite("R = ",_LOG_TEXT);
mikrobus_logWrite(text,_LOG_TEXT);
mikrobus_logWrite(" Ohms",_LOG_LINE);
value = multim_measureU();
FloatToStr(value,text);
mikrobus_logWrite("U = ",_LOG_TEXT);
mikrobus_logWrite(text,_LOG_TEXT);
mikrobus_logWrite(" mV",_LOG_LINE);
value = multim_measureI();
FloatToStr(value,text);
mikrobus_logWrite("I = ",_LOG_TEXT);
mikrobus_logWrite(text,_LOG_TEXT);
mikrobus_logWrite(" mA",_LOG_LINE);
value = multim_measureC();
FloatToStr(value,text);
mikrobus_logWrite("C = ",_LOG_TEXT);
mikrobus_logWrite(text,_LOG_TEXT);
mikrobus_logWrite(" nF",_LOG_LINE);
mikrobus_logWrite("‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐",_LOG_LINE);
Delay_ms( 1000 );
The full application code, and ready to use projects can be found on
our Libstock page.
Other MikroElektronika libraries used in the example:
Conversions
C_String
UART
Additional notes and information
Depending on the development board you are using, you may need USB UART
click, USB UART 2 click or RS232 click to connect to your PC, for development
systems with no UART to USB interface available on the board. The terminal
available in all MikroElektronika compilers, or any other terminal application
of your choice, can be used to read the message.
mikroSDK
This click board is supported with mikroSDK - MikroElektronika Software
Development Kit. To ensure proper operation of mikroSDK compliant click
board demo applications, mikroSDK should be downloaded from
the LibStock and installed for the compiler you are using.
For more information about mikroSDK, visit the official page.
https://www.mikroe.com/multimeter‐click 8‐20‐18
