Guru
Joined: 05/03/2018
Location: NetherlandsPosts: 5849
| Posted: 01:17pm 16 Dec 2022 |
Tom,
Can't look into your parts storage, but driving a low impedance speaker requires current. The simplest way to do that from a single cell is use a single cell class D amplifier. I thinks these are available on Aliexpress and others.
A quick alternative could be:
Take a 74HC244 (octal buffer), parallel all 8 channels (inputs tied to eachother, outputs tied to eachother). Run it from 3.7V. Pull enables low (otherwise it doesn't do much). Connect the 8 inputs to the PWM out pin on the PICO. GND=GND. Vdd = 3.7V.
In this configuration it will be a high current (200mA+) PWM output. From the common output an e-cap (100uF 16V) to the speaker. (other side speaker to GND). No filtering, done.
When that audio level is okay, we may add a filter between the speaker and the 74HC244. When not, you definitely need a class D amplifier.
- Use 74HC244, not 74HCT244, not 74LV244, not 74LS244.
Volhout
P.S. I know the pico runs 3.3V and the 74HC244 is connected to 3.7V/4.2V but logic levels will be okay enough for the demo.
Other multiple buffer chips in C-mos may also work (74HC04 (6 inverting buffers), 74HC14 (6 smitt trigger buffers), 74HC240 (8 inverting buffers)).
Edited 2022-12-16 23:20 by Volhout