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DMM Shield Reference Manual

The DMM Shield is a 5 1/2 Digit digital multimeter, designed for use with Digilent line of chipKIT microcontroller boards such as Uno32™, uC32™, WF32™, or Max32™ and FPGA boards that are equipped with the Arduino Shield such as Arty A7, Arty Z7-10, Arty Z7-20 or Arty S7, see Compatible Boards The shield is built around the HY3131 module from Hycon Technology, [http://www.hycontek.com/wp-content/uploads/DS-HY3131_EN.pdf] which is an analog front end DMM dedicated chip. The device has 7 measurements functions and is factory calibrated. It can be used out of the box with the compatible system boards line.

It is accessed through a custom SPI interface, using digital IO pins exposed in the DMM Shield connector.

Download This Reference Manual

Overview

Features

  • Full compatibility with all the line of Digilent System Boards featuring the Arduino Shield
  • Provides 4 banana connectors for measurements(Volts/Ω, COM, mAmps, Amps).
  • Floating COM
  • AC/DC voltage and current measurements
  • Diode, continuity measurement/function
  • Resistance measurement
  • Supports SPI connection.

HY3131 Features in Brief

  • Programmable multifunctional switch network
  • High-resolution, high-speed ∑-Δ ADCs - for high conversion speed, resolution and accuracy
  • Digital RMS circuit - the conversion result is processed by the high-speed calculation of the inner hardware to realize the digital RMS [reference: http://www.hycontek.com/wp-content/uploads/Description-HYCON-EN.pdf]
  • Operational amplifier
  • Multifunctional comparator
  • Peak-Hold measurement circuit - to achieve higher accuracy
  • Low-Pass filter - implements a third order LPF
  • Supports SPI interface connection.

Compatible Boards

The DMM Shield is compatible with all Digilent boards that use the Arduino Shield connector:


Specifications

Voltage and Power Parameters Min Typical Max Units
Power Supply Input Voltage 3.0 3.3 3.6 V
Power Supply Input Voltage - 5.0 - V
Power Supply Current Consumption - 90 100 mA
Ranges Min Max
AC Voltage -30 +30 V
DC Voltage -50 +50 V
AC/DC Current -5 +5 A
Resistances 50 50M Ω
  • Accuracy: +/-0.1% on Voltage, Current and 500Ω-5MΩ Resistance measurements; +/-1% on 50Ω and 50MΩ Resistances measurements
  • Resolution: 5 1/2 Digit
  • Floating COM with on board isolated power supply
  • Protections:
    • 60V PTC for Voltage and resistances and uA
    • 630mA fuse for mA rail
    • 6.3A fuse for A rail
  • Communication: Custom SPI protocol

Power

DMM Shield is powered by the system board. It uses both 5V0 and 3V3 power supplies.The average consumption of the DMM Shield is 90mA The DMM shield feature on-board power supplies that are used to power the DMM core of the board. The 5V power supply is isolated in order to provide an isolated reference signal for measurements. There can be found more than one reference signals on the DMM Shield board:

  • GND - Ground for the non-isolated section. References all the signals and voltage rails in the non-isolated section such as 5V0 and 3V3 voltages from the system board,relay driver,flash memory
  • VSS_ISO - Most negative voltage in the isolated section. It is the reference for isolated power supplies VCC5V0_ISO and VCC3V3_ISO as well for all the digital signals in the isolated section
  • COM_ISO - Reference for the DMM measurement. All the measurements done with the DMM Shield will be referenced to COM_ISO signal, through COM connector, J2. The reference is leveled at 1.8V above VSS_ISO
  • AGND_ISO - Reference for all the analog signals in the isolated section. It is connected to the COM_ISO through a 0Ω resistor

Functional Description

Connectors and Jumpers

DMM Shield is equipped with the Arduino Shield connector that interfaces it with the system board for powering and communication. Beside the shield, there are also 4 banana connectors that interface the DMM with the sources and devices that need to be measured.

Banana Connectors (J1-J4)

  • J1 (V/Ω)- is used for measuring the AC/DC voltages, Resistances, Diode and Continuity.
  • J2 (COM)- is the reference for all the measurements that can be done with the DMM Shield. COM signal is floating from all the other reference points from the board.
  • J3 (500mA)- is used for measuring AC/DC currents up to 500mA.
  • J4 (5A) - is used for measuring AC/DC currents up to 5A.

Arduino Shield Connector (J5-J9):

  • J5 - 1×2 Header -Digital pins
  • J6 - 2×6 Header - Analog pins.
  • J7, J8 - 2×8 Headers - Digital pins.
  • J9 - 1×8 Header - Power pins.
  • For detailed usage of each pin please see the Pinout Table Appendix Pinout Table Appendix.

Jumpers:

  • JP1- Frequency Measurement - Not Implemented

Digital Pins used for communication

SPI Pins The DMMShield supports SPI communication with both the DMM chip and the EEPROM chip. The hardware interface lines DataIn, DataOut and Clock are shared between the two devices, and the Chip Select lines are separate, allowing the user to access either of them with less hardware resources used. The DMM chip is electrically separated from the rest of the circuitry, therefore the communication lines need to be isolated as well. The EEPROM CS line is active high, while the DMM CS line is active low. The reading sequence for SPI DMM communication is the one below: The writing sequence for SPI DMM communication is the one below: The interrupt request sequence for SPI DMM communication is the one below: The timing for SPI DMM communication is the one below:

GPIO Pins There are three GPIO pins used for Relays control: RLU, RLD, RLI. Depending on the type of measurement performed, the corresponding relay/s need to be triggered/commanded using a GPIO pin.

EEPROM memory

The DMMShield is equipped with a non-volatile EEPROM memory chip: Microchip 93LC66BT(see http://ww1.microchip.com/downloads/en/DeviceDoc/21795E.pdf), having 512 bytes/256 words (4kbits) available space. The memory can be accessed over a custom SPI protocol, using digital IO pins exposed in the DMMShield connector: CS_EEPROM (EEPROM SPI chip select), DO (SPI MISO), DI (SPI MOSI) and CLK (SPI CLK).

While the chip select line is specific to EEPROM module, the SPI lines (data and clock) are shared with the DMM device.

Note the data is written and read from memory using word format addressing, instead of byte: bytes 0-1 are written at address 0x00, bytes 2-3 are written at address 0x01, etc.

The EEPROM is used to store the following system information:

Section Content Addresses (words) Size
Factory calibration data 0x93 – 0xFF 109 words / 218 bytes
Serial Number 0x8C – 0x92 7 words / 14 bytes
User calibration data 0x1F – 0x8B 109 words / 218 bytes
Free Memory 0x00 – 0x1E 31 words / 62 bytes

Please consult the DMM Shield Library User Guide for more information about the EEPROM module usage and communication. For more details about Calibration process, read more on Calibration Procedure below.

Measurement Scales

DMM Shield comes with preset scales of measurement. They will indicate the maximum value that can be accurately measured with the device. While the range of each one is from 0 to full scale, keep in mind that at low values the resolution is lower and different scales might give a more accurate result since is calibrated closer that value Ex: for a 40kΩ resistor is better to use the 50kΩ scale instead of the 500kΩ for a better resolution. There are 4 scales for voltages, 5 for current and 7 for resistances.

Scales - - - - - - - -
AC Voltage 50m 500m 5 30 - - - V
DC Voltage 50m 500m 5 50 - - - V
AC/DC Current 500u 5m 50m 500m 5 - - A
Resistances 50 500 5k 50k 500k 5M 50M Ω

The device comes factory calibrated for each scale. For more details about calibration please see the Calibration procedure below.

Setting each scale assumes the configuration of some registers and three relays.The relays RLI, RLU and RLD are controlled by IO2, IO3 and IO4 from the shield connector.

Scales RLI RLU RLD
50MΩ 0 0 1
5MΩ 0 0 1
500kΩ 0 0 1
50kΩ 0 0 1
5kΩ 0 0 1
500Ω 0 0 1
50Ω 0 0 1
50VDC 0 1 0
5VDC 0 1 0
500mVDC 0 0 1
50mVDC 0 0 1
50VAC 0 1 0
5VAC 0 1 0
500mVAC 0 0 1
50mVAC 0 0 1
5ADC 0 0 0
500mADC 0 0 0
50mADC 0 0 0
5mADC 1 0 0
500uADC 1 0 0
5AAC 0 0 0
500mAAC 0 0 0
50mAAC 0 0 0
5mAAC 1 0 0
500uAAC 1 0 0
Continuity 0 0 1
Diode 0 0 1

The HY3131 chip provides 23 registers to be able to configure the scales.

Scales INTE R20 R21 R22 R23 R24 R25 R26 R27 R28 R29 R2A R2B R2C R2D R2E R2F R30 R31 R32 R33 R34 R35 R36
50MΩ 0x00 0xC0 0xCF 0x17 0x93 0x85 0x00 0x00 0x55 0x55 0x00 0x00 0x08 0x00 0x00 0x80 0x86 0x80 0xD1 0x3C 0xA0 0x00 0x00 0x00
5MΩ 0x00 0xC0 0xCF 0x17 0x93 0x85 0x00 0x00 0x55 0x55 0x00 0x00 0x08 0x00 0x80 0x80 0x86 0x80 0xD1 0x3C 0xA0 0x00 0x00 0x00
500kΩ 0x00 0xC0 0xCF 0x17 0x93 0x85 0x00 0x00 0x55 0x55 0x00 0x00 0x08 0x00 0x08 0x80 0x86 0x80 0xD1 0x33 0x20 0x00 0x00 0x00
50kΩ 0x00 0xC0 0xCF 0x17 0x83 0x85 0x00 0x00 0x55 0x00 0x00 0x00 0x40 0x00 0x06 0x44 0x94 0x80 0xD3 0x33 0x20 0x00 0x00 0x00
5kΩ 0x00 0xC0 0xCF 0x17 0x83 0x85 0x00 0x00 0x55 0x00 0x00 0x00 0x40 0x60 0x00 0x44 0x94 0x80 0xD3 0x33 0x20 0x00 0x00 0x00
500Ω 0x00 0xC0 0xCF 0x17 0x83 0x35 0x00 0x00 0x55 0x00 0x00 0x00 0x40 0x06 0x00 0x44 0x94 0x80 0xD2 0x3C 0xA0 0x00 0x00 0x00
50Ω 0x00 0xC0 0xCF 0x17 0x83 0x35 0x01 0x00 0x55 0x00 0x00 0x00 0x40 0x06 0x00 0x44 0x94 0x80 0xD2 0x3C 0xA0 0x00 0x00 0x00
50VDC 0x00 0x60 0x00 0x17 0x8B 0x01 0x11 0x00 0x55 0x31 0x00 0x22 0x00 0x00 0x09 0x28 0xA0 0x80 0xC7 0x33 0x20 0x00 0x00 0x00
5VDC 0x00 0x60 0x00 0x17 0x8B 0x01 0x11 0x00 0x55 0x31 0x00 0x22 0x00 0x00 0x90 0x28 0xA0 0x80 0xC7 0x33 0x20 0x00 0x00 0x00
500mVDC 0x00 0xC0 0x00 0x17 0x8B 0x85 0x11 0x00 0x55 0x31 0x00 0x00 0x00 0x00 0x00 0x00 0x90 0x80 0xC7 0x33 0x28 0x00 0x00 0x00
50mVDC 0x00 0x00 0x00 0x17 0x8B 0x35 0x11 0x00 0x55 0x31 0x00 0x00 0x00 0x00 0x00 0x00 0x90 0x80 0xC7 0x3C 0x60 0x00 0x00 0x00
50VAC 0x00 0xF2 0xDD 0x07 0x03 0x52 0x10 0x80 0x25 0x31 0xF8 0x22 0x00 0x00 0x0D 0x28 0xA0 0xFF 0xC7 0x38 0x20 0x00 0x00 0x00
5VAC 0x00 0xF2 0xDD 0x07 0x03 0x52 0x10 0x80 0x25 0x31 0xF8 0x22 0x00 0x00 0xD0 0x88 0xA0 0xFF 0xC7 0x38 0x20 0x02 0x50 0x0C
500mVAC 0x00 0x92 0xDD 0x07 0x03 0x52 0x10 0x80 0x25 0x11 0xF8 0x00 0x00 0x00 0x00 0x00 0x90 0x80 0xC7 0x3A 0x28 0x00 0x00 0x00
50mVAC 0x00 0x52 0xDD 0x07 0x03 0x00 0x13 0x80 0x25 0x11 0xF8 0x00 0x00 0x00 0x00 0x00 0x90 0x80 0xC7 0x3A 0x28 0x00 0x00 0x00
5ADC 0x00 0x00 0x00 0x17 0x8B 0x95 0x11 0x00 0x55 0x31 0x00 0x00 0x00 0x00 0x00 0x00 0x80 0x80 0xC7 0x33 0x20 0x00 0x00 0x00
500mADC 0x00 0x00 0x00 0x17 0x8B 0x95 0x11 0x00 0x55 0x31 0x00 0x00 0x00 0x00 0x00 0x00 0x80 0x80 0xC7 0x33 0xA0 0x00 0x00 0x00
50mADC 0x00 0x00 0x00 0x17 0x8B 0x35 0x11 0x00 0x55 0x31 0x00 0x00 0x00 0x00 0x00 0x00 0x80 0x80 0xC7 0x3D 0x20 0x00 0x00 0x00
5mADC 0x00 0x00 0x00 0x17 0x8B 0x95 0x11 0x00 0x55 0x31 0x00 0x00 0x00 0x00 0x00 0x00 0x80 0x80 0xC7 0x33 0x20 0x00 0x00 0x00
500uADC 0x00 0x00 0x00 0x17 0x8B 0x35 0x11 0x00 0x55 0x31 0x00 0x00 0x00 0x00 0x00 0x00 0x80 0x80 0xC7 0x3D 0xA0 0x00 0x00 0x00
5AAC 0x00 0x52 0xDD 0x07 0x03 0x00 0x13 0x80 0x25 0x11 0xF8 0x00 0x00 0x00 0x00 0x00 0x90 0x80 0xC7 0x3D 0x28 0x00 0x00 0x00
500mAAC 0x00 0x92 0xDD 0x07 0x03 0x52 0x10 0x80 0x25 0x11 0xF8 0x00 0x00 0x00 0x00 0x00 0x90 0x80 0xC7 0x3D 0x28 0x00 0x00 0x00
50mAAC 0x00 0x52 0xDD 0x07 0x03 0x00 0x13 0x80 0x25 0x11 0xF8 0x00 0x00 0x00 0x00 0x00 0x90 0x80 0xC7 0x3D 0x28 0x00 0x00 0x00
5mAAC 0x00 0x92 0xDD 0x07 0x03 0x52 0x10 0x80 0x25 0x11 0xF8 0x00 0x00 0x00 0x00 0x00 0x90 0x80 0xC7 0x3D 0x28 0x00 0x00 0x00
500uAAC 0x00 0x52 0xDD 0x07 0x03 0x00 0x13 0x80 0x25 0x11 0xF8 0x00 0x00 0x00 0x00 0x00 0x90 0x80 0xC7 0x3D 0x28 0x00 0x00 0x00
Continuity 0x00 0x74 0xCF 0x17 0x83 0x35 0x10 0x00 0x55 0x00 0x00 0x00 0x00 0x0A 0x00 0x40 0x86 0x80 0xD2 0x3C 0xA0 0x00 0x00 0x00
Diode 0x00 0xC0 0xCF 0x17 0x8B 0x8D 0x10 0x00 0x55 0x31 0x00 0x00 0x00 0x08 0x00 0x40 0x86 0x80 0xE2 0x33 0xA0 0x00 0x00 0x00

For more information please see the Library :FIXME:

Accuracy

The accuracy of the DMM Shield is around 0.1% for AC/DC Currents and Voltages, 500Ω-5MΩ Resistances and within the scales; 1% for 50Ω and 50MΩ Resistances. For AC Current and Voltage we guarantee the 0.1% accuracy at 50/60Hz. Note that outrunning the end of a scale will increase the measurement error. The accuracy is computed in percentage as a difference between the reference value and the measured value, reported to full scale.

Let's consider $R_{F}, M_{F}$ as the reference and the measured value at full scale and $F_{S}$ the full scale. The accuracy is computed as follows:

$$Accuracy=\frac {R_{F} - M_{F}}{F_{S}} * 100\label{10}\tag{10}$$

Calibration procedure

The DMMShield needs calibration before performing measurements and delivering correctly measured values to the user. This is due to errors introduced by the chip itself and on-board additional electronics. Calibration is the process of computing and applying correction coefficients to the measured values that allow precise measurements.

The process consists of computing an additive and a multiplicative coefficient for each scale.

Basically calibration is done by collecting pairs of reference value and measured value (RefVal, MsVal) in multiple points. The reference value is the value measured with an accurate instrument, considered to be the actual value to be measured by the DMMShield device. The measured value is the value reported by DMMShield hardware. When all these pairs are collected, the calibration coefficients are computed mainly using the difference between the reference and the measured values.

Depending on the scale, different types of calibration are performed, as detailed in the following chapters:

2 points Calibration for Resistance scales

This method applies to the Resistance scales. It collects the pairs (RefVal, MsVal) in two points: 0 point (short between probes), and full scale value.

Let’s consider this pairs as being ($R_{0}$, $M_{0}$) and ($R_{F}$, $M_{F}$). The calibration coefficients are computed in the following manner:

$$Calib_{MULT}=\frac {R_{0} - R_{F}}{M_{0} - M_{F}} - 1\label{1}\tag{1}$$ $$Calib_{ADD}=(R_{0} - M_{0})(1 + Calib_{MULT})\label{2}\tag{2}$$

The reference value for the short is considered to be 0: $R_{0} = 0$

The calibration coefficients are applied to the acquired value in the following manner: $$Value_{corrected}=(1 + Calib_{MULT})Value_{acquired} + Calib_{ADD}\label{3}\tag{3}$$

3 points Calibration for DC

This method applies to the DC Voltage and DC current scales. It collects the pairs (RefVal, MsVal) in three points: 0 point (short between probes), negative full scale value and positive full scale value. For example, for VoltageDC500m scale, the following points are used: 0 point (short between probes), -500mV, 500 mV.

Let’s consider this pairs as being ($R_{0}$, $M_{0}$), ($R_{FN}$, $M_{FN}$) and ($R_{FP}$, $M_{FP}$). The calibration coefficients are computed in the following manner:

$$Calib_{MULT}=\frac {R_{FP} - R_{FN}}{M_{FP} - M_{FN}} - 1\label{4}\tag{4}$$ $$Calib_{ADD}=(R_{0} - M_{0})(1 + Calib_{MULT})\label{5}\tag{5}$$

The reference value for the short is considered to be 0: $R_{0} = 0$

The calibration coefficients are applied to the acquired value: $$Value_{corrected}=(1 + Calib_{MULT})Value_{acquired} + Calib_{ADD}\label{6}\tag{6}$$

2 points Calibration for AC

This method applies to the AC Voltage and AC current scales. It collects the pairs (RefVal, MsVal) in two points: 0 point (short between probes) and full scale value. For example, for VoltageAC500m scale, the following points are used: 0 point (short between probes) and 500 mV.

Let’s consider this pairs as being ($R_{0}$, $M_{0}$), ($R_{F}$, $M_{F}$). The calibration coefficients are computed in the following manner: $$Calib_{MULT}=\frac {R_{F}}{\sqrt{{M_{F}}^2 - {M_{0}}^2}} - 1\label{7}\tag{7}$$ $$Calib_{ADD}= M_{0}\label{8}\tag{8}$$

The reference value for the short is considered to be 0: $R_{0} = 0$

The calibration coefficients are applied to the acquired value: $$Value_{corrected}=(1 + Calib_{MULT})\sqrt{| {Value_{acquired}}^2- {Calib_{ADD}}^2 |}\label{9}\tag{9}$$

Software Libraries

We created libraries that can be used with the DMM Shield. The libraries were created to support ZYNQ plaforms and MPLAB. Documentation and downloads for these libraries can be found at the following locations:


Appendix: Pinout Tables

DMM Shield Connector Pinout


Banana Connector Interface

J1 J2 J3 J4
Voltage/Ω COM Current (mA) Current (A)

Power Connector

J9
Connector pin number Arduino Shield Name
1 NC
2 IOREF
3 RST
4 3V3
5 5V0
6 GND
7 GND
8 VIN

Analog Connector

J6
Top Row Bottom Row
Connector pin number Arduino Shield Name Connector pin number Arduino Shield Name
1 A0 2 A6
3 A1 4 A7
5 A2 6 A8
7 A3 8 A9
9 A4 10 A10
11 A5 12 A11

Digital IO Connector

J7
Bottom Row Top row
Connector pin number Arduino Shield Name Connector pin number Arduino Shield Name
1 IO41 2 A
3 IO40 4 G
5 IO39 6 IO13/CLK
7 IO38 8 IO12/DI
9 IO37 10 IO11/DO
11 IO36 12 IO10/CS_DMM
13 IO35 14 IO9/CS_EEPROM
15 IO34 16 IO8
J8
Bottom Row Top Row
Connector pin number Arduino Shield Name Connector pin number Arduino Shield Name
1 IO33 2 IO7
3 IO32 4 IO6
5 IO31 6 IO5
7 IO30 8 IO4/RLD
9 IO29 10 IO3/RLU
11 IO28 12 IO2/RLI
13 IO27 14 IO1
15 IO26 16 IO0

* Pullup resistors for pins SCL1 and SDA1 can be enabled by shorting jumpers JP1 and JP2, respectively.

Pins #5 and #11 of each Pmod port are tied to Ground. Pins #6 and #12 of each Pmod port are tied to the HAT Adapter's 3V3 rail.


About this Document

This reference manual applies to Revision C of the DMM Shield.


Additional Information

* The DMM Shield Schematic can be found here.


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