What Is Being Built?

In basic layman’s terms, the aim is to build a device that should have the following engineering specifications:

• The device must be able to measure a voltage signal at its input without significantly modifying the operation of the circuit being tested

• The device should be able to measure a time-varying signal up to some defined frequency limit, and potentially down to DC on the lower end

• The device should be able to accept a range of positive and negative input voltages, ideally with as wide a range as possible

• The device should be able to display or visualize this information and perform measurements accurately

• The device should be self-contained, portable, and low-cost to manufacture

To dive in deeper, the intended use case is for general engineering projects where the design should be able to take measurements from common circuits such as microcontrollers (requiring high-frequency range), motors & mechanical elements (requiring high voltage range), and op-amps, sensors, etc. (requiring an AC/DC option, low noise, and other features).

Oscilloscope showing a trace with standard inputs and controls

User using an oscilloscope found in the market

How Will It Look Like?

• The design should have two input ranges, called 1X mode and 10X mode. These correspond to matching types of oscilloscope probes that one can purchase and use with the design.

• When a 1X scope probe is connected and 1X mode is set for your oscilloscope:

  • The input at the oscilloscope probe and your circuit should accept a raw input voltage signal in the range of +15 V to -15 V.

  • The input impedance (equivalent resistance relative to ground/0V looking ‘into’ your oscilloscope) should be at least 1MΩ, ideally much more.

• When a 10X scope probe is connected and 10X mode is set for your oscilloscope:

  • The input at the oscilloscope probe will accept a raw input voltage signal in the range of +150 V to -150 V. Your circuit will continue to accept an input range of +15 V to -15 V.

  • The input impedance of your circuit must be exactly 1MΩ.

• When either mode is being used:

  • The scope has a 20 pF capacitance terminating the scope input.

  • The circuit should attenuate frequency content above 20 kHz to some degree.

• Has a switch for coupling which allows either AC or DC coupling:

  • In DC coupling mode, the incoming signal is measured unchanged.

  • In AC coupling mode, the DC component of the incoming signal must be blocked, but low-frequency signal content should otherwise be attenuated as little as possible.

Black Box Diagram for 1X Mode

Black Box Diagram for 10X Mode

The goal will now be to unearth what the designs for Circuit 1 (Input Stage) and Circuit 2 (Power Supply) should be. The eventual aim, however, is to encompass all circuitry designs that work as an oscilloscope into a 3” x 4” PCB that can easily be connected to a laptop to display signal.

Circuit 1 Input Stage

Circuit 1 Schematic

It is to be noted that a normal oscilloscope design would encompass a range protection system at the inputs. This has not been taken into consideration in Circuit 1. Thus, we will make it one of our goals to add such circuitry now. To summarize, our additional stages that will add to Circuit 1 are as follows:

Stage A: A protection circuit that will connect between the BNC connector and V IN Circuit 1 Schematic.

Stage B: A low-pass filter that connects to the V OUT of Circuit 1 Schematic.

Stage C: A protection circuit that will connect to the output of the low-pass filter. This protection circuit’s output will then connect to an ADC Input pin on the Arduino Nano.

Visual Representation of Stages A, B and C integrated with Circuit 1

Below are the circuitry developed for Stages A, B and C integrated within the circuity system of Circuit 1 Schematic.

Stage A integrated with Circuit 1

Circuit 1 integrated with Stages B and C (connected to Arduino Nano)

Circuit 2 Power Supply

Circuit 2 Schematic