This code example demonstrates the usage of two multi-configurable OPA modules, integrated onto the PIC18F56Q71 microcontroller. This project leverages both OPA channels, similar to the Getting Started with OPA module on the PIC18F16Q41
- PIC18F56Q71 Curiosity Nano User Guide
- PIC18F56Q71 Curiosity Nano Device Page
- PIC18F16Q41 Curiosity Nano Firmware Demo
- MPLAB® X IDE 6.10 or newer
- MPLAB® XC8 2.41 or a newer compiler
- MPLAB® Code Configurator (MCC) 5.3.7 or newer
- Microchip PIC18F-Q Series Device Support (1.20.405) or newer
- PIC18F56Q71 Curiosity Nano (EV01G21A)
- Curiosity Nano Adapter board (AC164162)
- Proto Click (proto-click) with modifications
In this example, the PIC18F56Q71 is used as the microcontroller.
The Curiosity Nano Adapter board enhances the capabilities of the PIC® MCU, and provides the user with easily adaptable mikroBUS™ headers.
A PROTO Click will be used to house the voltage potentiometers, status LEDs, logic switches, and a reset button.
| Front | Back |
|---|---|
 |
 |
This is the modified board, which includes four potentiometers, four logic switches, two LEDs, and a reset button.
The op amp configuration is determined based on the logic levels of Channel 1 pins (RC6, RC3), and Channel 2 pins (RC1, RC4). To select the OPA configuration, set the pins according to the table below. After setting the pins to match the desired OPA configuration, SW0 must then be pressed to update the OPA module configuration and resume operation. The PIC18F56Q71 operates in Sleep mode with the OPA enabled when not being reconfigured.
| RC6/RC3 | RC1/RC4 | Configuration |
|---|---|---|
| 0 | 0 | 1 - Connected directly to external pins |
| 0 | 1 | 2 - Unity Gain Buffer / Voltage Follower |
| 1 | 0 | 3 - Non-Inverting Programmable Gain Amplifier (PGA) |
| 1 | 1 | 4 - Inverting Programmable Gain Amplifier (PGA) |
Please note that Weak Pull-ups are enabled on switch pins in this code example, so unless each pin is directly connected to ground they will read as logic '1' when setting up the OPA module configuration.
In this configuration, both of the OPA inputs and the output is connected directly to the corresponding I/O pins. This allows the OPA to be used on its own with external discrete components to provide a feedback network and achieve a specific functionality.
| OPAMP | OPA1IN+ | OPA1IN- | OUTPUT |
|---|---|---|---|
| OPA1 | RA5 (OPA1IN2+) | RA2 (OPA1IN0-) | RA1 (OPA1OUT) |
| OPA2 | RB3 (OPA2IN2+) | RB2 (OPA2IN3-) | RB1 (OPA2OUT) |
In this configuration, the OPA is configured as a unity gain buffer (voltage follower). When configured in this mode, only positive input of the OPA (OPAxIN+) and the output (OPAxOUT) are connected to the external I/O pins, while the negative input of the OPA (OPAxIN-) is internally connected to the output of the OPA as shown in the figure below to form a unity gain buffer.
| OPA | Positive Input | Output (OUT) |
|---|---|---|
| OPA1 | RA5 (OPA1IN2+) | RA1 (OPA1OUT) |
| OPA2 | RB3 (OPA2IN2+) | RB1 (OPA2OUT) |
In this configuration, the OPA is configured as a non-inverting programmable gain amplifier and uses the internal resistor ladder built into the OPA module. The positive input (OPAxIN+) and the output (OPAxOUT) of the OPA are connected to the corresponding I/O pins. The OPA is preconfigured with a gain of '4' using the internal resistor ladder. This gain can be changed by writing a different value to the GSEL bits of OPA1CON1 in the function named void OPA_NonInverting(void) located in application.c.
| OPA | Gain | Positive Input | Output (OUT) |
|---|---|---|---|
| OPA1 | 4 | RA5 (OPA1IN2+) | RC2 (OPA1OUT) |
| OPA2 | 4 | RB3 (OPA2IN2+) | RB1 (OPA2OUT) |
In this configuration, the OPA is configured as an inverting programmable gain amplifier and used the internal resistor ladder built into the OPA module. The OPA is preconfigured with a gain of '3' using the internal resistor ladder. This gain can be changed by writing a different value to the GSEL bits of OPAxCON1 in the function named void OPA_Inverting(void) located in application.c.
| OPA | Gain | Positive Input | Output (OUT) |
|---|---|---|---|
| OPA1 | 3 | RA2 (OPA1IN2-) | RC2 (OPA1OUT) |
| OPA2 | 3 | RB2 (OPA2IN3-) | RB1 (OPA2OUT) |
This shows channel 1 in configuration 3 (Non-Inverting Programmable Gain Amplifier), and channel 2 in configuration 2 (Unity Gain Buffer). The user can determine which configuration the device is currently on, by watching the status LEDs blink or by checking the Terminal.
The image above is the screen displayed in your chosen terminal upon startup or after a reset.
The image above is what the terminal window will display after releasing SW0. The message will vary based on the configuration of the OPA.