Analog Signals

Analog signals are different from digital signals in that they can be any voltage and can vary continuously and smoothly between voltages. An analog signal is like a dimmer switch on a light, whereas a digital signal is like a simple on/off switch. 

Digital signals only can ever have two states, they are either are on (high logic level voltage like 3.3V) or off (low logic level voltage like 0V / ground).

By contrast, analog signals can be any voltage in-between on and off, such as 1.8V or 0.001V or 2.98V and so on.

Analog signals are continuous values which means they can be an infinite number of different voltages. Think of analog signals like a floating point or fractional number, they can smoothly transiting to any in-between value like 1.8V, 1.81V, 1.801V, 1.8001V, 1.80001V and so forth to infinity.

Many devices use analog signals, in particular sensors typically output an analog signal or voltage that varies based on something being sensed like light, heat, humidity, etc. Some examples of sensors with analog outputs:

• Microphones
• Photocells (light sensitive resistors)
• Temperature sensors
• Force-sensitive resistors
• Flex sensors
• Thermistor (temperature sensitive resistor)
• Ultraviolet light sensor
• Light sensors
• Distance sensor
• Anemometer (wind speed sensor)
• Resistive touch screen
• Ultrasonic distance sensor
• Liquid level sensor
• Potentiometer (variable resistor)

Wire the Pots

The four potentiometers will act as voltage dividers, sending anywhere from 0V to 3.3V to their respective ADC pins on the PCF8591.

Voltage dividers work by connecting one of the outer pot legs to ground, the other outer leg to positive voltage (in this case 3.3V), and then the center (wiper) leg to an analog input pin on the ADC.

On a breadboard, you can connect your pots as shown here.

Perf Board

For this finished project, you'll connect your ADC board and pots on a perf board. The perf board has lots of solder points, but none of them are connected by default as is the case with a breadboard. So, you'll wire everything directly.

This diagram shows the connections necessary, however you'll do the wiring underneath the board, so this image is a bit like an x-ray view.

Solid core hook-up wire works well for this type of hand-wired trace circuit.

Once you've built the circuit, you should use a multimeter in continuity mode to test that you don't have any shorts.

CYBERDECK Hat

The CYBERDECK Hat is perfect for adding accessories to the RPi 400. It breaks out all of the GPIO pins at a useful angle, plus it adds convenient STEMMA QT/Qwiic plugs for easy I2C use.

The CYBERDECK also gives us a great place to mount additional boards. This mounting plate allows us to add the knob board to the CYBERDECK.

Download the model from the link below and print it in PLA at 0.2mm layer height, 60% infill.

With the Pi powered off, insert the CYBERDECK Hat into the GPIO pin slot, being careful to align the pins properly.