Precision Voltage Monitor Kit

Classes 9-10, typical ages 14–16. Age ranges vary by learner. Guided low-voltage electronics.

Activity engagement

75–105 minutes. Explore 15–20 min · Build 25–35 min · Test and discuss 35–50 min. Estimated time for building, testing and discussion.

What you need

A computer with a USB port and Arduino IDE is required and is not included.

Included components

• Small Breadboard / Mini Solderless Board - 400 points — 1 breadboard
• Jumper Wire Combo - Male to Male, Male to Female and Female to Female Breadboard Connecting Wires (10 Qty Each) — 1 set
• Illustrated Activity Guide and Observation Sheets — 1 set
• Fitted Headers and Labelled Connection Leads — 1 set
• Arduino Uno R3 CH340G version compatible Arduino Development Board — 1 controller board
• USB A to B Programming Cable for Arduino Uno/ Arduino Mega — 1 data cable
• DT9205A Digital Multimeter with Probes and Battery — 1 multimeter
• 10K Ω 1/4 Watts (10 PCS) — 2 resistor (individual units)
• 4 CELL AA BATTERY HOLDER WITH SWITCH / COVER — 1 holder
• AA BATTERY — 4 battery (individual units)

What you learn

• A divider scales the input before an ADC measures it.
• Reference voltage and resistor tolerance affect accuracy.
• Calibration needs a separate reference instrument.

Connection guide

• Isolated battery holder positive → 10 kOhm → A0 midpoint → 10 kOhm → battery negative. Battery negative also → Uno GND.
• Power Uno only by USB. Do not connect battery positive to Uno 5 V, USB or another rail.
• Multimeter COM/V socket only, DC volts mode; input limited to 0–9 V DC.

Steps to make it

1. Disconnect all power and identify the supplied part labels and pinouts before wiring.
2. Measure the two divider resistors with power off and inspect the separated battery circuit.
3. Upload and compare the reported voltage with the meter across the four-AA holder.
4. Measure the Uno 5 V rail with the meter and replace vRef in the sketch with that measured value.
5. Repeat measurements with two and four AA cells using the holder connection guide; switch off before altering cells.
6. Change only the named parameter for the extension, repeat the controlled trials, save observations and disconnect power afterward.

Programming resources

Arduino IDE: select Arduino Uno and the USB port. Use the supplied USB data cable. Serial Monitor/Plotter: 115200 baud.

Uses the selected board core libraries.

Download starter sketch

Test challenge

Compare uncalibrated and reference-adjusted errors at two battery voltages.

Observation task

Meter voltage, raw ADC mean, assumed reference, calibrated estimate and percentage error.

Expected result

Divider-scaled estimates approach the multimeter reading after reference adjustment; this is not a precision-certified meter.

If it does not work

Check the common ground, midpoint and input limit. Never use mains, a vehicle battery or the meter current socket.

Try next

Include measured resistor values in the scaling equation instead of assuming a perfect 1:1 divider.

Use and supervision

Use only the supplied low-voltage DC parts. Disconnect power before rewiring; check polarity and labelled pinouts. No soldering or exposed mains connections. Adult guidance is recommended.

How this experiment works

Download class activity guide

Cover illustrations show component types. Functional animations explain principles and are not recorded prototype tests. Follow the supplied connection labels and pinouts.