Are the Workbench Devices Turned Off?

Contents List

1. Introduction to the Project
2. What Is the Project?
3. Project Components and Model Numbers
4. Brief Overview of Each Circuit Component
5. Workbench Loads to Be Monitored
6. Exact Loads to Be Connected to the Project Circuit
7. Detailed Circuit Schematic and Interconnections
8. How the Project Measures Current
9. How the Project Determines Whether a Device Is OFF
10. OFF, Standby, and ON Detection
11. Suggested Current Thresholds
12. Calibration of the Current Sensors
13. Software Platform
14. Displaying the Workbench Status
15. Monitoring the Workbench Through Wi-Fi
16. Understanding the Measurements
17. Electrical Safety Considerations
18. Possible Project Improvements
19. Frequently Asked Questions
20. Conclusion

Reading Time is 20 minute

1. Introduction

An electronics workbench can contain several devices that are used throughout the day, including soldering stations, bench power supplies, monitors, chargers, development boards, test equipment, computers, and other electronic tools.

At the end of a work session, it is common to switch these devices off and assume that they are no longer consuming electricity.

However, switching a device off does not always mean that its electrical consumption has reached zero.

Some electronic equipment can continue to draw a small amount of current while connected to the electrical supply. This may happen because internal circuits remain powered for functions such as status indicators, memory retention, network connectivity, remote control, or quick startup.

This project explores a practical question:

Are the devices on an electronics workbench really turned off, or are some of them still consuming electricity?

To answer this question, we can build a 10-channel workbench current-monitoring system using an ESP32, multiple ADS1115 analog-to-digital converters, and ten non-invasive SCT-013 current transformers.

The system measures the current associated with each connected load and uses calibrated thresholds to classify each device as OFF, STANDBY, or ON.

The project is useful for beginners because it introduces practical concepts such as current sensing, analog-to-digital conversion, RMS measurement, microcontrollers, I²C communication, and threshold-based device detection. It can also be expanded by hobbyists and engineers with Wi-Fi monitoring, data logging, graphs, and additional measurement capabilities.

2. What Is the Project?

The project is a 10-channel workbench device current-monitoring system based on a D1 Mini ESP32 development board.

Each of the ten workbench loads is monitored by its own SCT-013 100A/1V split-core current transformer. The sensors provide an isolated, non-invasive method of sensing the AC current flowing to the monitored equipment.

Because the ESP32 does not directly provide ten suitable external analog measurement channels for this design, three ADS1115 16-bit, 4-channel ADC modules are used to acquire the sensor signals.

The basic architecture is:

10 × SCT-013 100A/1V → 3 × ADS1115 → D1 Mini ESP32 → SSD1306 OLED

The ESP32 processes the sampled current signals, calculates RMS current, and compares the measured values with calibrated thresholds.

The system can then indicate:

• OFF — current is below the OFF threshold.
• STANDBY — current is present but below the normal operating threshold.
• ON — current reaches or exceeds the ON threshold.

The first version is designed as a current-monitoring and device-state detection system, not as a precision energy meter.

3. Project Components and Model Numbers

The following component list is based on the revised Makers Electronics parts selected for this project.

Component	Recommended Makers Product / Specification	Quantity
Main controller	D1 Mini ESP32 WiFi + Bluetooth Development Board	1
ADC	ADS1115 16-Bit ADC 4-Channel with Programmable Gain Amplifier	3
AC current sensor	SCT-013 100A/1V Split-Core Current Transformer	10
OLED display	OLED Display I²C 4 Pin 0.96″, 128×64	1
Bias resistors	10 kΩ, 0.25 W through-hole resistors	20+
ADC input resistors	100 kΩ through-hole resistors	10
Coupling capacitors	1 µF 100Vcapacitors	10
Decoupling capacitors	100 nF 50V ceramic capacitors	As required
Supply capacitors	10 µF 400V capacitors	As required
DC power supply	5V 700 mA / 3W AC/DC power-supply module	1
Terminal connectors	KF128/KF129 terminal blocks	As required
Jumper wires	20 cm / 30 cm jumper wires	As required
Prototype board	830-point breadboard or suitable Vero board	1
Enclosure	Black Plastic Project Box 75 × 55 × 30 mm	1

The component selection has been changed from the earlier design so that the project is based on the new Makers Electronics component list.

Important: The current sensor used in this revised design is the SCT-013 100A/1V, not the previously specified SCT-013-010. Therefore, the current-scaling and calibration must be based on the actual 100A/1V sensor.

4. Brief Overview of Each Circuit Component

D1 Mini ESP32 WiFi + Bluetooth Development Board

The D1 Mini ESP32 is the main controller of the project.

It receives the digitized current measurements from the ADS1115 modules, processes the samples, calculates RMS current, determines the operating state of each load, and controls the OLED display.

Its Wi-Fi capability also provides a foundation for adding a browser-based monitoring dashboard in a future version.

ADS1115 16-Bit ADC

The ADS1115 is a 16-bit, four-channel analog-to-digital converter with a programmable gain amplifier.

Each module provides four analog input channels. Three modules therefore provide twelve available channels, which is enough for the ten current sensors used in this project.

The ADS1115 modules communicate with the ESP32 through the I²C interface.

SCT-013 100A/1V Current Transformer

The SCT-013 100A/1V is a split-core AC current transformer.

It can be clipped around a single current-carrying conductor without making a direct electrical connection to that conductor.

For this project, one SCT-013 sensor is assigned to each workbench load.

Because this sensor is rated for 100 A input and 1 V output, the signal conversion in the software must be based on this sensor’s actual characteristics and verified through calibration.

0.96-Inch SSD1306 OLED Display

The 128×64 I²C OLED provides a compact visual interface for the project.

It can display the name of each monitored device, its measured current, and its detected operating state.

10 kΩ Resistors

The 10 kΩ resistors are used to create the reference/bias network required to shift the AC sensor signal into a voltage range suitable for the ADC.

Two matched 10 kΩ resistors can be used to create a nominal midpoint reference from the 3.3 V logic supply.

100 kΩ Resistors

The 100 kΩ resistors provide the required input biasing for the AC-coupled sensor signals.

1 µF Capacitors

The 1 µF capacitors are used as AC-coupling capacitors between the current-transformer outputs and the ADC input stages.

100 nF Ceramic Capacitors

These capacitors are used for local high-frequency supply decoupling around the electronic modules.

10 µF Capacitors

The 10 µF capacitors provide additional local supply filtering and help reduce supply-voltage fluctuations.

5 V AC/DC Power-Supply Module

The 5 V power-supply module provides the low-voltage DC supply required by the electronics.

The supply must be installed safely because the input side is connected to mains voltage.

KF128/KF129 Terminal Blocks

Terminal blocks provide convenient and secure connections for the low-voltage wiring and sensor connections.

Jumper Wires

Jumper wires are useful during prototyping and for connecting the ESP32, ADS1115 modules, OLED, and other low-voltage components.

Prototype Board

An 830-point breadboard can be used while developing and testing the low-voltage circuit. A more permanent version can be transferred to a suitable Vero board or custom PCB.

Project Enclosure

The plastic project box provides mechanical protection for the low-voltage electronics.

The enclosure size may need to be increased if the final assembly includes additional terminals, wiring, power-supply hardware, or mains-side components.

5. Workbench Loads to Be Monitored

The project is designed to monitor ten common electronics-workbench loads:

• Bench Power Supply
• Soldering Station
• Computer Monitor
• USB Charger
• Development Board Power Supply
• Oscilloscope
• Function Generator
• 3D Printer
• Network Equipment
• Laptop Charger

The objective is to monitor each load independently rather than measuring the combined current of the entire workbench.

6. Exact Loads to Be Connected to the Project Circuit

Each load receives its own current sensor.

Channel	Monitored Load	Current Sensor
CH1	Bench Power Supply	SCT-013 100A/1V #1
CH2	Soldering Station	SCT-013 100A/1V #2
CH3	Computer Monitor	SCT-013 100A/1V #3
CH4	USB Charger	SCT-013 100A/1V #4
CH5	Development Board Power Supply	SCT-013 100A/1V #5
CH6	Oscilloscope	SCT-013 100A/1V #6
CH7	Function Generator	SCT-013 100A/1V #7
CH8	3D Printer	SCT-013 100A/1V #8
CH9	Network Equipment	SCT-013 100A/1V #9
CH10	Laptop Charger	SCT-013 100A/1V #10

Each SCT-013 should monitor one load only.

This allows the ESP32 to determine which individual device is consuming current.

7. Detailed Circuit Schematic and Interconnections

The main circuit can be divided into four functional sections:

Current Sensors → Signal Conditioning → ADS1115 ADCs → ESP32/OLED

The ten SCT-013 sensors are distributed across three ADS1115 modules.

ADS1115 Channel Assignment

ADC Module	ADC Channel	Workbench Load
ADS1115 #1	A0	Bench Power Supply
ADS1115 #1	A1	Soldering Station
ADS1115 #1	A2	Computer Monitor
ADS1115 #1	A3	USB Charger
ADS1115 #2	A0	Development Board Power Supply
ADS1115 #2	A1	Oscilloscope
ADS1115 #2	A2	Function Generator
ADS1115 #2	A3	3D Printer
ADS1115 #3	A0	Network Equipment
ADS1115 #3	A1	Laptop Charger
ADS1115 #3	A2	Spare
ADS1115 #3	A3	Spare

I²C Connections

The three ADS1115 modules and the OLED share the ESP32’s I²C bus.

Example addresses are:

• ADS1115 #1 → 0x48
• ADS1115 #2 → 0x49
• ADS1115 #3 → 0x4A
• OLED → 0x3C

The exact address configuration depends on how the ADS1115 address pins are connected.

Sensor Signal Connection

Each SCT-013 output is connected to an AC-coupling and bias network before reaching an ADS1115 analog input.

The general signal path is:

SCT-013 → 1 µF coupling capacitor → ADC input → 100 kΩ bias resistor → VBIAS

A midpoint bias voltage is created from the low-voltage supply using matched resistors so that the AC waveform is centered within the ADC’s positive input range.

Important Current-Transformer Installation

The SCT-013 must be placed around one current-carrying conductor only.

Do not pass both live and neutral conductors through the same current transformer because their magnetic fields can substantially cancel, resulting in an incorrect or very small measurement.

The mains-side installation must remain physically separated from the low-voltage electronics.

8. How the Project Measures Current

The SCT-013 100A/1V produces an AC voltage corresponding to the current flowing through the monitored conductor.

The ADS1115 samples this waveform and sends the digital measurements to the ESP32 through I²C.

The ESP32 can calculate RMS current using:

I_RMS = √[(I₁² + I₂² + … + I_N²) / N]

RMS current provides a useful representation of the magnitude of an AC current waveform.

However, the exact conversion from measured ADC voltage to current must be calibrated for the SCT-013 100A/1V used in this project.

The software should therefore not blindly reuse the conversion factor from the previous SCT-013-010 design.

9. How the Project Determines Whether a Device Is OFF

The project does not determine the state of a device by checking its physical power switch.

Instead, it measures the current flowing to the device.

If the measured current remains below the calibrated OFF threshold, the system classifies the device as OFF.

If a small current remains after the device has apparently been switched off, the system can classify the device as STANDBY.

This makes the system useful for identifying equipment that continues to consume electricity when it is not actively being used.

10. OFF, Standby, and ON Detection

The system uses three states:

State	Meaning
OFF	Measured current is below the OFF threshold
STANDBY	Current is above the OFF threshold but below the ON threshold
ON	Current reaches or exceeds the ON threshold

This three-state approach is more informative than a simple ON/OFF indicator.

It is especially useful for equipment such as monitors, chargers, networking equipment, and laboratory instruments that may continue consuming current after their primary function has been disabled.

11. Suggested Current Thresholds

The following values can be used as initial example thresholds for software development and testing:

Load	OFF → Standby	Standby → ON
Bench Power Supply	< 0.03 A	≥ 0.15 A
Soldering Station	< 0.04 A	≥ 0.20 A
Computer Monitor	< 0.03 A	≥ 0.08 A
USB Charger	< 0.02 A	≥ 0.05 A
Development Board Power Supply	< 0.02 A	≥ 0.06 A
Oscilloscope	< 0.04 A	≥ 0.15 A
Function Generator	< 0.03 A	≥ 0.10 A
3D Printer	< 0.04 A	≥ 0.30 A
Network Equipment	< 0.05 A	≥ 0.12 A
Laptop Charger	< 0.03 A	≥ 0.10 A

These are suggested starting values, not measured specifications for particular commercial devices.

The actual thresholds should be determined experimentally after the equipment is connected.

Because the revised design uses the 100A/1V SCT-013, the low-current measurement resolution should also be evaluated carefully. Very small standby currents may be close to the practical noise floor of the complete sensor/ADC circuit.

12. Calibration of the Current Sensors

Calibration is particularly important in this project because the system is intended to distinguish relatively small differences between OFF, standby, and normal operation.

For each load:

1. Connect the device to its assigned monitoring channel.
2. Measure the current while the device is OFF.
3. Measure the current while the device is in standby, if applicable.
4. Measure the current during normal operation.
5. Record the measured values.
6. Compare the measured values with the initial thresholds.
7. Adjust the OFF and ON thresholds as necessary.
8. Repeat the process for all ten loads.

For example, if a monitor measures approximately 0.01 A when OFF, 0.03 A in standby, and 0.12 A during operation, the thresholds can be selected between those measured states.

The calibration values should be stored in the C++ program or, in a future version, saved in non-volatile memory so that they can be changed without recompiling the program.

13. Software Platform

The recommended software platform is:

D1 Mini ESP32 + Arduino IDE + ESP32 Arduino Core + C/C++

The program performs the following main tasks:

1. Initializes the ESP32.
2. Initializes the three ADS1115 modules.
3. Initializes the OLED display.
4. Reads the ten current channels.
5. Calculates RMS current.
6. Converts the sensor signal into an estimated current value.
7. Compares the current with the calibrated thresholds.
8. Determines whether each load is OFF, STANDBY, or ON.
9. Displays the results on the OLED.
10. Sends measurement information to the Serial Monitor.
11. Provides a foundation for future Wi-Fi monitoring.

C++ HTML Source Code File 

14. Displaying the Workbench Status

The 0.96-inch 128×64 OLED has limited display space.

Displaying ten devices with their names, current values, and operating states simultaneously would make the text difficult to read.

Therefore, the project can use multiple pages.

For example:

Page 1

• Bench Power Supply
• Soldering Station
• Computer Monitor
• USB Charger
• Development Board Supply

Page 2

• Oscilloscope
• Function Generator
• 3D Printer
• Network Equipment
• Laptop Charger

Each device can be displayed with its approximate current and state.

Example:

Monitor
0.03 A — STANDBY

This makes the status easy to understand at a glance.

15. Monitoring the Workbench Through Wi-Fi

The D1 Mini ESP32 includes Wi-Fi capability, allowing a future version of the project to provide a web-based dashboard.

A browser-based interface could display:

• Device name
• Measured current
• OFF / STANDBY / ON status
• Number of active devices
• Number of devices in standby
• Current readings
• Historical measurements
• Possible unnecessary consumption

This would transform the project from a simple local monitor into a smart workbench monitoring system.

16. Understanding the Measurements

It is important to distinguish between current, power, and energy.

Current

Current is the quantity directly measured by the SCT-013 current transformer.

It tells us how much electrical current is flowing through the monitored conductor.

Power

Electrical power depends on both voltage and current. For AC loads, the phase relationship and waveform characteristics can also affect real power.

Therefore, current alone cannot provide an accurate measurement of real power for every type of load.

Energy

Energy is the amount of electrical work consumed over time, normally expressed in watt-hours or kilowatt-hours.

Accurate energy measurement requires appropriate voltage and power measurements and integration over time.

Therefore, this project should be described as a:

10-channel AC current-monitoring and device-state detection system

rather than a precision energy meter.

17. Electrical Safety Considerations

This project monitors equipment connected to mains electricity, so safety must be treated as a fundamental part of the design.

The SCT-013 provides non-invasive current sensing, but the monitored conductors and mains connections remain potentially dangerous.

Follow these precautions:

• Use appropriately rated mains cables and connectors.
• Keep mains wiring physically separated from the low-voltage electronics.
• Use an appropriate insulated enclosure.
• Provide proper strain relief.
• Use correctly rated terminal blocks.
• Never work on energized mains wiring.
• Never expose mains conductors inside an accessible enclosure.
• Place the SCT-013 around only the intended conductor.
• Do not exceed the sensor’s specified operating conditions.
• Ensure the 5 V power-supply module is installed according to its electrical requirements.
• Have mains-side wiring performed or checked by a suitably qualified person where required.

The initial version of the project should remain monitor-only. It should not directly switch mains loads.

18. Possible Project Improvements

Once the basic monitoring system is working, several improvements can be added.

Wi-Fi Dashboard

Create a web interface that displays all ten loads in real time.

Data Logging

Store current measurements so the user can review equipment usage over hours, days, or weeks.

Graphs

Display current trends for individual devices.

Notifications

The ESP32 could notify the user when equipment remains in standby for a specified period.

Improved Calibration

Add an interface that allows the user to change each device’s thresholds without modifying the source code.

More Monitoring Channels

The two unused ADS1115 channels can provide additional flexibility for future expansion.

Real Power Measurement

Additional voltage and phase measurement circuitry can be added if the project is later developed into a real-power or energy-monitoring system.

Automatic Load Control

A future version could use appropriately rated, isolated switching hardware to control selected loads. Such an upgrade would require a separate safety-focused design for mains switching.

19. Frequently Asked Questions

Can the project detect whether a device is completely turned off?

Yes, but it detects the device state by measuring its AC current rather than directly detecting the position of the power switch.

If the measured current remains below the calibrated OFF threshold, the system classifies the device as OFF.

If the device continues to draw a small amount of current, it can instead be classified as STANDBY.

Why are three ADS1115 modules required?

Each ADS1115 provides four analog input channels.

The project has ten independent current sensors, so three ADS1115 modules provide twelve available inputs.

This gives the project enough channels for all ten loads while leaving two channels available for possible future expansion.

Why is the SCT-013 100A/1V used in this revised project?

The SCT-013 100A/1V is the current-transformer model selected from the revised Makers Electronics component list.

It provides a voltage output corresponding to the AC current flowing through the monitored conductor and allows non-invasive current measurement.

The software and calibration must be designed specifically around this sensor.

Can one current sensor monitor multiple devices?

Not if the system needs to determine the state of each device individually.

Each monitored load should have its own SCT-013.

If several devices share one sensor, the sensor measures their combined current and the system cannot determine which device is responsible for the measured current.

Why must the SCT-013 surround only one conductor?

The current transformer responds to the magnetic field produced by current flowing through a conductor.

If both live and neutral conductors are passed through the same CT, their magnetic fields can substantially cancel because the currents flow in opposite directions.

The resulting measurement can therefore be very small or incorrect.

Can the project accurately measure the power consumed by each device?

Not with the current-monitoring hardware alone.

The SCT-013 measures current, but accurate real-power measurement also requires suitable voltage and phase information.

Therefore, this version of the project should be considered a current-monitoring and device-state detection system.

Can the OLED display all ten devices at once?

Technically, information can be compressed onto the display, but doing so would make the text difficult to read.

A better solution is to use two or more display pages, with approximately five devices per page.

Can the current thresholds be changed?

Yes.

The thresholds are software-defined and can be adjusted for each monitored device.

The example thresholds in this article are starting values only. The actual thresholds should be determined through calibration with the specific equipment being monitored.

Can the project work without Wi-Fi?

Yes.

The basic system can operate locally using the ESP32, ADS1115 modules, and OLED display.

Wi-Fi is an optional feature that can be added for remote monitoring, web dashboards, and data logging.

What happens if a device has an extremely low standby current?

Very low standby currents can be difficult to distinguish from sensor noise and measurement errors.

This is especially important when monitoring low-current electronic devices with a high-range 100A/1V current transformer.

For this reason, actual measurements should be taken during calibration before selecting the final thresholds.

Does the project measure every type of electrical load equally well?

Not necessarily.

Different devices can have different current waveforms, startup currents, standby behavior, and power factors.

The project is intended for typical electronics-workbench equipment, but every load should be tested and calibrated individually.

Can the project be expanded beyond ten devices?

Yes.

The three ADS1115 modules provide twelve analog channels, of which ten are currently used.

The remaining two channels can be used for additional measurements, subject to the limitations of the complete circuit and software.

Additional ADC modules can also be considered for a larger system.

Can the project automatically turn equipment off?

The basic project is monitor-only.

It detects and displays equipment status but does not disconnect the loads from mains power.

Automatic switching can be considered as a future enhancement using properly rated and isolated switching hardware with appropriate electrical-safety measures.

20. Conclusion

The Are the Workbench Devices Turned Off? project provides a practical way to monitor the current consumption of equipment commonly found on an electronics workbench.

Using ten SCT-013 100A/1V current transformers, three ADS1115 ADC modules, a D1 Mini ESP32, and a 0.96-inch OLED display, the system can monitor ten separate loads and classify them as OFF, STANDBY, or ON.

The revised component selection also makes the project easier to build around the components selected from Makers Electronics, including the controller, ADC modules, current sensors, display, passive components, connectors, wiring, power supply, prototype board, and enclosure.

More importantly, the project demonstrates several practical electronics concepts in one system, including AC current sensing, signal conditioning, analog-to-digital conversion, RMS calculations, I²C communication, embedded C/C++ programming, calibration, and device-state detection.

The system can begin as a simple local monitoring device and later be expanded with Wi-Fi, data logging, graphs, notifications, and more advanced electrical measurements.

With proper calibration and safe mains-side construction, it can become a useful tool for answering a simple but important workbench question.