Measuring Negative Voltages with Arduino: A Delayed Solution

When working with analog-to-digital converters (ADCs), one of the common challenges faced is measuring negative voltage levels. In this article, we will explore a solution to overcome this limitation using an Arduino board and its internal reference voltage.

The problem lies in the fact that most ADCs, including those found on microcontrollers like ATmega328P, are single-ended and measure voltages with respect to ground (Gnd). This means that they can only measure positive voltage levels relative to Gnd. To measure negative voltages, we need a way to create a 'virtual' or 'floating' reference point, also known as the COM node.

A common approach is to use an Analog Front End (AFE) or signal conditioning circuit to generate this COM node. This can be achieved using a voltage divider network, which allows us to scale down the input voltage and bring it closer to Gnd. However, this method has limitations and may not always provide accurate results.

In this particular design, we are using an Opamp-based circuit with a 5-Mega Ohm resistor in parallel with a 100-Kilo Ohm resistor, which is connected to the output of the second Opamp. This circuit provides a voltage divider network that brings the input signal (550 mV) down to a level that can be measured by the ADC.

The key component here is the LM324 Opamp, which is used to buffer the 1.1-V reference voltage from the first Opamp's output. This allows us to measure voltages between Gnd and AREF range, effectively doubling our measurement range.

To enable this feature, we need to internal reference AREF on the ATmega328P microcontroller by setting it up in the firmware or code during the setup phase. Once enabled, we can use the AREF pin as a reference voltage for our ADC measurements.

The benefits of this design are twofold. Firstly, it allows us to measure negative voltages relative to the COM node, which is set at half AREF voltage (550 mV). Secondly, it provides an effective range of 0 to 1.1 volts for our ADC measurements, making it suitable for a wide range of applications.

In conclusion, measuring negative voltages with Arduino requires some creative problem-solving and attention to detail. By understanding the limitations of single-ended ADCs and using Opamp-based circuits to generate a COM node, we can overcome these limitations and achieve accurate measurements in both positive and negative voltage ranges.

Arduino delay negative