SOUND PLAYER BASED ON RPI PICO

Sound player based on Raspberry Rpi Pico. Sound data are stored in onboard memory. Very few external (easy to find & solder) components required. The project was designed to be in sleep mode for a very long time powered by batteries. Can be used for musical wall clocks, talking dolls, toys, etc.

Here is a complete project using this board: https://galopago.github.io/english/halloween-talking-clock-based-on-rpi-pico/

Working principle

The circuit (see schematic) has been designed to stay most of the time in silence powered by 2 AA batteries, like musical wall clocks or talking toys. In the best scenario, Rpi Pico in in deep sleep mode, will drain approx 1.3 mAh from the batteries. A pair of AA batteries in series have around 2000 mAh of juice, just in standby they will last only for two months. Unacceptable!.

An external circuit was added to totally power off Rpi Pico via 3V3_EN pin. Draining just only 70 uAh, which translates to 3 years of standby. Much better!

The circuit work in the following manner: In standby mode, a capacitor with a large resistor holds the conduction voltage of a MOSFET which is in charge of tying 3V3_EN to ground, powering off the board completely. To play a sound, click briefly on the push button which discharges the capacitor and stops conduction of the MOSFET. Now 3V3_EN pin is tied to V+ via its internal pull up, powering on the Rpi Pico Board. Once powered on and program booted, it keeps the capacitor discharged via a GPIO while sound is played. When the sound ends, the RPI Pico puts the GPIO in high impedance state, so the capacitor charges again and Rpi Powers off until the next click on the button!

There are many stored sounds in the Rpi Pico, and they are played in sequence. To know which sound needs to be played in the next click, some data needs to be preserved between power offs, that data is stored in the internal flash memory. Be careful modifying the program to keep flash writes to a minimum.

The program was written using the Rpi Pico SDK and more or less the same functionality also in CircuitPython too!