Let's Make Robots!

Stop burning speakers with your Picaxe chips

On Picaxe:

sound 1, (110,3)

is NOT a good idea, you should allways write

sound 1, (110,3) low 1

(you do not need line breaks, just write it as above)


Being used to burning things and changing rechargable batteries all the time, I did not really wonder that much that a tiny speaker or two has been fried while having fun with robots and Picaxe over time (mainly 28' these are the only ones this is tested on).

Now I am building a new robot that has a speaker underneath it.. Lifting it up from a test, I felt that the speaker was burning hot!!

Picaxe is leaving the port to "High" after the "Sound" command!!! So the speaker is just getting continious voltage after a "sound".

This means battery drain, and it means burnt speakers after a while, if your robot have just at any point made a small beep!

Crap, Picaxe! (But I still love you) - Must be a bug, no? Or some reason I don´t get??

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picaxe_manual3.pdf shows a 10uF capacitor in sereies with a speaker, though the speaker says 40ohm i believe, and the one i yanked out of an old alarm clock radio says 16ohm, so.....we'll see. Looks like i gott make another trip to radioshack. Thanks frits!

No need - just make a habit out of making it

sound 1, (110,3) low 1

Sounds like making a brick wall in front of your teenage-son's car to stop him from drunk driving, no? Would it not be better to take the keys?

get me? :) (or is it me? I know no electronics, I admit!)

Thanks, Dave, hope someone (else?) can work this out :)

/ Frits

I feel the capacitor should be at least 1 uF or larger.

WARNING: to anyone reading this: If "tech-stuff" makes your head hurt, do not read the following. 

      (ha ha)

Carsten, when you suggested a capacitor in the range ~22nf up to ~10 uF, I disagree.

22nF would be about 72000 ohms at 100 Hz. and 7200 ohms at 1 kHz. This is going to cut down an already low audio component to such a low level as to make it quite hard to hear. [ Only 694 microamps at 1 kHz. giving about three and a half milliwatts through the speaker.]

Therefore, I would say the value should be at least 1 uF (which would be ~160 ohms @ 1 kHz and ~1K6 @ 100 Hz.) or larger.


Refering to the the other post above, the manual does show 10 uF with a 40 ohm speaker. 10 uF is 16 ohms reactance at 1000 Hz and less at higher frequencies. At higher frequencies (higher pitched tones) the current draw from the picaxe would relate mostly to the 40 ohms of the speaker and could be as much as 5v / 40 ohms = 125 mA.  This actually concerns me because the current drain on any picaxe lead is supposed to be no more than 20 mA.  Now admittedly the audio component will be a fluctuating or intermittant value, so it is probably okay.  However, I think some amplification is needed because even pushing the picaxe close to the limit like this, the sound level is quite low.

I will do a blog page and go into more detail on how to fix this.

Thanks, Dan :)

And this IS an old post.. but 2 things, I think some of you are missing:

A) The speaker is hooked up to a buffered output, a Darlington.

B) The point is that after the sound command was initiated, the darlington kept the speaker up(or down, depending on wiring)

There has been a lot of updates since this, I am not even sure it is the case any longer :)

I was not denegrating your design. I was mostly referring to the sample in the manual -part 3, where they do not show any amplification, but a direct hookup to the picaxe. 


OOoohhh k-n-o-w-l-e-d-g-e! Thank you!!

/ Fritsl

6-7 months later: I never get to solder all them components, I just set the port low, as written in the original post. it works without problems!
Could you put a small capacitor in series with the speaker to block the DC?  I don't know what value would be appropriate, though.