The last article on adding louder amplified sound to your projects went into a lot of detail so that you could add amplified sound to any of your projects even if it didn’t quite fit the examples being shown. Downside was that it could get a little complex for some, with various factors that need to be considered in order to implement different power ratings of speakers. So here I present the simplified version where all you need do is look up your speaker in a table in order to know which resistor is required. There is one other caveat… and that is I will present two tables, one for 3.3V projects and one for 5V projects. But for most people who look at this website and follow my videos these will be the two most common voltages used by far.
A video is available that supports this article;
The basic Audio amplifier circuit
The basic circuit is shown below and will be the same no matter what project you attach it to.
One restriction is that the speaker must be 8Ω (OK, higher is OK but NOT lower), but you will find plenty of 8Ω speakers at whatever electronic component supplier source you use (i.e. eBay, AliExpress, Banggood, RS, Farnell etc. etc.) The problem being they come in all sorts of different shapes and sizes with correspondingly different power ratings. In general, as you can imagine, the higher the power rating the louder the speaker can be, but of course you also have limits one what your circuit can cope with. In order to ensure you do not break your components (from the MCU to the speaker itself) the value for the resistor R2 must be carefully calculated based on several factors. As mentioned, the previous article went into this. But what you want as a quick hobbyist is to buy a speaker and for a given wattage just be told what resistor value R2 should be, and that’s what this article does.
The tables for R2
So there are two tables, one for a 3.3V based system and one for a 5V based system. All you need do is look up the power rating for your speaker to get the value of resistor to use for R2.
3.3V Projects
| Power (W) | R2 (Ω) |
|---|---|
| 0.25 | 160 |
| 0.5 | 330 |
| 1 | 680 |
| 1.5 and above | 1000 |
5V Projects
| Power (W) | R2(Ω) |
|---|---|
| 0.25 | 68 |
| 0.5 | 150 |
| 1.0 | 300 |
| 1.5 and above | 390 |
That should cover nearly every project typical users of this site will use, if you have different voltage needs then you will have to read the original article, all for now, hope this has been helpful in getting some more powerful audio than piezo speakers into out projects 🙂