Arduino Powered Multimeter

Introduction: Arduino Powered Multimeter

In this project, you will be building a voltmeter and ohmmeter using the digitalRead function of an Arduino. You will be able to get a reading almost every millisecond, much more precise than a typical multimeter. Finally, the data can be accessed on the Serial monitor, which then can be copied onto other documents if you want to analyze the data.

Additionally, since typical Arduinos are limited to only 5V, an adaptation of the potential divider circuit will allow you to change the maximum voltage that the Arduino can measure.

Supplies:

1) 1 x Arduino nano/Arduino Uno + Connecting cable

2) 5cm x 5cm Perfboard

3) 20 x jumper cables or wires

4) 1 x 1K resistor

5) 2x resistors of the same value (doesn't matter what the values are)

6) 1 x 16x2 LCD screen (Optional)

7) 1 x DB107 bridge rectifier (Can be replaced with 4 diodes)

8) 1 x 100K or 250K potentiometer

9) 6 crocodile clips

10) 1 x Latching push switch

11) 1 x 9V battery + connector clip

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Step 1: Acquiring the Materials

1) 1 x Arduino nano/Arduino Uno + Connecting cable

2) 5cm x 5cm Perfboard

3) 20 x jumper cables or wires

4) 1 x 1K resistor

5) 2 x resistors of the same value (doesn't matter what the values are)

6) 1 x 16x2 LCD screen (Optional)

7) 1 x DB107 bridge rectifier (Can be replaced with 4 diodes)

8) 1 x 100K or 250K potentiometer

9) 6 crocodile clips

10) 1 x Latching push switch

11) 1 x 9V battery + connector clip

Most items can be purchased off amazon. There are a couple electronics kits on amazon which provide you with all of the basic components such as resistors, diodes, transistors, etc. The one I have found to give me a bang for my buck is available on this link.

I personally had most of the components already as I do a lot of these types of projects. For the inventors out there in Singapore, Sim Lim Tower is the place to go to purchase all electronic components. I recommend Space electronics, Continental electronics, or Hamilton electronics on the 3rd floor.

Step 2: Planning and Explaining the Circuitry

The circuit is actually slightly more complicated than you might expect. This circuit makes use of potential dividers (link to help explain potential dividers) to measure the resistance and add the feature of variable maximum voltage for the voltmeter aspect.

Similar to how a multimeter can measure voltage at various stages, 20V, 2000mV, 200mV so on and so forth, the circuit allows you to vary the maximum voltage the device can measure.

I will just go over the purpose of the various components.

1) Arduino is used for its analogRead function. This allows the Arduino to measure the potential difference between the selected analog pin and its ground pin. Essentially the voltage at the selected pin.

2) The potentiometer is used to vary the contrast of the LCD screen. Building on that the LCD screen will be used to display the voltage.

3) The two resistors of the same value are used to create the potential divider for the voltmeter part of the multimeter. One resistor will be soldered onto the perfboard while the other resistor is connected using crocodile clips. When you want more precision and a max voltage of 5V, you would connect the crocodile clips together without any resistor in between. When you want a max voltage of 10V you would connect the second resistor between the crocodile clips.

4) The bridge rectifier is used to turn any AC current, maybe from a dynamo, into DC. Additionally, you now don't have to worry about positive and negative wires when measuring the voltage.

5) The 1K resistor is used to make the potential divider for the ohmmeter. The drop in voltage, measured by the analogRead function, after 5V is inputted into the potential divider will indicate the value of the R2 resistor.

6) The latching push switch is using to switch the Arduino between the Voltmeter mode and Ohmmeter mode. When the button is on, the value is 1, the Arduino is measuring the Resistance. When the button is off, value is 0, the Arduino is measuring the Voltage.

Step 3: Putting Together the Circuit

There are a couple of options on how to put together the circuit.

1) For people getting into electronics, I would recommend using the breadboard to build the circuit. It is a lot less messy than soldering, and it will be easier to debug because the wires can be adjusted easily. Follow the connections shown on the fritzing images.

2) For more experienced individuals, try out using soldering the circuit onto the breadboard. It will be more permanent and last longer. Read and follow the schematic for guidance.

3) Finally, you can also order a pre-made PCB from SEEED. All you would have to do it solder the components on. The necessary Gerber file is attached in the step. Here is a link to a google drive folder with the zipped gerber file: https://drive.google.com/drive/folders/1BiDizfdqELH9Jw2WzIk26-8mdwan7ch5?usp=sharing

Step 4: Code for the Arduino

It is pretty self-explanatory. Details can be found in the code itself in the form of comments.

Step 5: Casing Once the Circuitry Is Completed

1) You can any old plastic case for its casing. Using a hot knife to cut out the slots for the LCD and button.

2) Additionally, you can check out my account for another instructable where I describe how to build a box out of laser cut acrylic. You will be able to find a svg file for the laser cutter. Alternatively, for people who don't have access to a laser cutter, you can find another instructable detailing how to build a box out of spare pieces of timber

3) Finally, you can just leave the circuit without a casing. It will be easy to repair and modify.

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