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# DMM = Digital MultiMeter.

Arduino library for a DMM (digital multimeter) class.


## Description

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.


#### Related

- https://github.com/RobTillaart/ACS712 (current measurement).


## Interface

```cpp
#include "DMM.h"
```

#### Constructor

- **DMM()** constructor.

#### Configuration

- **begin(uint8_t analogPin, float volts = 5.0, uint16_t maxADC = 1023)** configuration.
Note these are the specifications of the ADC used. 
- **void  setMaxVoltage(float maxVoltage)**
- **float getMaxVoltage()**
- **void  setGain(float factor = 1.0)** GAIN e.g. due to voltage divider.
A 25V to 5V divider has a factor = 5.
- **float getGain()** returns the set gain.


#### ReadVolts

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.
- **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.


#### ReadOhm

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)


#### Calibration

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


## Operation

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


## Future

#### Functional

- AMPS  (how -> measure voltage over a known resistor)
- CAPS  (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


#### Must

- 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.


#### Should

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



#### Could

- multichannel compare
- schema for
- scope functionality?


#### Won't