Arduino library for a DMM (digital multimeter) class.

Experimental

DMM is a class that uses the Arduino analogRead to make measurements. It is based upon the UNO but will work on some other boards too.

The first version only works as a voltmeter, DC only. It is meant to be extended in the future to be a complete Digital MultiMeter class. that includes amps ohms, diode testing etc.

This is an old 'toy' project, wrapped into a class. Do not expect high precision or accuracy.

Feedback as always is welcome.

• https://github.com/RobTillaart/ACS712 - current measurement
• https://github.com/RobTillaart/INA226 - voltage + current + power
• https://github.com/RobTillaart/printHelpers - engineering formatting of numbers.

#include "DMM.h"

• DMM() constructor.

• begin(uint8_t analogPin, float volts = 5.0, uint16_t maxADC = 1023) configuration. Note these are the specifications of the ADC used. The defaults are a 10 bit 5.0 volt ADC (UNO R3). Typical values for maxADC = 255 (8 bit), 1023 (10 bit), 4095 (12 bit), 16383 (14 bit), 65535 (16 bit). The parameters are not checked on their range.
• void setMaxVoltage(float maxVoltage) configure the maximum voltage.
• float getMaxVoltage() returns set max voltage.

• void setGain(float factor = 1.0) GAIN e.g. due to voltage divider. A 25V to 5V divider has a factor = 5. In theory the gain can be negative, or smaller than 1.0. The parameter is not checked on range to maximize "freedom of use".
• float getGain() returns the set gain. default = 1.0.

One must connect GND of Arduino to the GND of the device.

    [A0]---- V unknown
   [GND]---- GND

or with a divider => setGain(x)

    [A0]----[divider]---- V unknown
   [GND]----[divider]---- GND

• float readVolts(uint8_t times = 1) read voltage. Times can be set to average multiple measurements to reduce the effects of noise.
• float readMilliVolts(uint8_t times = 1) convenience wrapper.
• float readNoise(uint8_t times = 1) measure the noise on the wire. Assumes connected to constant voltage e.g. GND.

The schema for measuring resistors is based on a simple voltage divider. See below. This schema can be extended with a selector switch that can switch between different reference resistors.

   [GND] ----[ R reference ]----[A0]----[ R unknown ]----[+5V]

• void setReferenceR(uint32_t ohm = 1000) set the reference resistor. units are Ohm, default = 1K.
• uint32_t readOhm(uint8_t times = 1) read Ohm. Times can be set to average multiple measurements.
• uint32_t readKiloOhm(uint8_t times = 1) read Ohm. Times can be set to average multiple measurements.

Character ohm = Ω (ALT-234 or ALT-0216 might work)

• float readNoise(uint8_t times = 1) get noise level for accuracy.

Basic operation is to connect the Arduino GND to the projects GND (or - ) and use the configured analog pin to measure a (positive) voltage.

By adding a voltage divider one can measure larger voltages. The divider factor can be set with setGain(factor).

To elaborate.

• GND, VCC

• AMPERE
  • how -> measure voltage over a known small resistor load.
  • use internal 1.1V?
• CAPACITY
  • how -> RC timing
  • RC (load 5 seconds)
  • disconnect
  • measure drop rate / time in micros.
• DIODE (how -> 5V or 0V)
  • DigitalRead(INPUT PULLUP) => HIGH or LOW
  • or 0.7 volt drop from 5V

• update documentation
• update examples
• add use of AREF
  • external or internal 1.1 Volt
• float setOffset(float offset) adjust the voltage used.
  • this is not the voltage the ADC uses internally.

• investigate noise
• analogReference(EXTERNAL) for external voltage for build in ADC
• support external ADC e.g. ADS1115 for 16 bit resolution.

• multichannel compare
• schema for
• scope functionality?

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Thank you,