# Why is my loudspeaker not working? From Make: Electronics

I am a complete beginner in the world of electronics and I am following the amazing book by Charles Platt, Make: Electronics (second edition). I am stuck at Experiment 11, when I need to connect an oscillator to a loudspeaker. The picture shows the circuit I am trying to make. It's an oscillator. It does work with a LED, but not with the loudspeaker. I do hear a very faint click when the capacitor discharge, but no sound. The loudspeaker is a 8ohm as indicated in the book. This is a picture. I know it's not super clear, but consider that the top part works as it should, it's the part with the speaker that possibly has something wrong.

To check that everything was working I also added a LED and made a video (and a switch to control it), here: https://youtu.be/UkEZzxmkfes It shows that the oscillator works ok, but the loudspeaker doesn't.

Am I connecting the loudspeaker the wrong way? Is it possible that the loudspeaker is broken?

More generally, since I am a complete noob, how would I go debugging this / giving people the proper information in order to help them helping me? Thanks!

• the way you put the flywires into your speaker contacts will not lead to a contact that you can rely on, either. Do what's necessary to increase the frequency of your oscillator, and fix the contacting. – Marcus Müller Jan 14 at 21:39
• Also, I'm kind of angry with Make magazine: in case (and I very much hope you will!) end up drawing electronic schematics yourself at some point, please: Do give every resistor a name of its own (R1, R2, ...) and every capacitor (C1, ...) and.. you get the idea. It's impossible to talk about circuits if you need to say things like "the fifth resistor from the top right that runs horizontal, noooo, the other right". – Marcus Müller Jan 14 at 21:41
• I used a 5V supply and changed the base resistors to 47k and changed the frequency capacitors to 22nF then the frequency became an audio sound of 667Hz. – Audioguru Jan 14 at 22:07
• @MarcusMüller: don't be too angry. I am teaching kids from age 8 up. They have enough issues recognizing symbols. That's why over time I go through different phases of wiring diagrams like in color with values directly written to components, black and white with short values and using a part list. – Thomas Weller Jan 15 at 15:14
• @ThomasWeller these are pretty awesome! – Marcus Müller Jan 15 at 15:30

The frequency of oscillation is determined by the 470 kΩ resistors and 3.3 μF capacitors and will be roughly $$\ \frac 1 {RC} = \frac 1 {470k \times 3.3\mu} = 0.64 \ \text{Hz}\$$. i.e., less than one pulse per second. The circuit has been optimised for the LED rather than the speaker.

Modify the circuit so that the frequency is 100 to 1000 times higher and you should be delighted. Note that if you put the LED back in you won't be able to see it blink (due to your persistence of vision) although if you can wave the breadboard back and forth you may be able to see a "dashed" line of light.

• Thanks, I'll try that tomorrow and report back :) – Vaaal88 Jan 14 at 22:11
• This^^ If the LED were operated at audio frequencies, you wouldn't be able to see it blinking (most people have trouble distinguishing blinking from steady at around 60Hz or higher) – Kyle B Jan 14 at 22:26
• It means reference the above post... i.e. I am agreeing with you ;) I only added a further detail about LED flashing frequency by putting a lower limit on it – Kyle B Jan 15 at 0:25
• It worked amazingly! Thanks also for the explanation youtube.com/watch?v=w0OUBY1dUzk&feature=youtu.be – Vaaal88 Jan 15 at 9:20
• Good work! With the pot in there I guess you are modifying the timing on one side. That means you are adjusting the pulse width (either the on time or the off time) and this has the dual effect of modifying the frequency but also the tone due to the change in the harmonics. The LED can be seen to dim too due to the changing ratio of on:off timing. – Transistor Jan 15 at 10:43

The oscillator you have is a multi-vibrator. It outputs a square wave. A square wave of low frequency sounds like a series of clicks when fed to a loud-speaker.

At a higher frequency, as square wave sounds like a buzz. At even higher frequencies, it begins to have an "electronic music" type of sound.