I've been busy with programming to try and source for a replacement speaker.
I'd prefer to replace the speaker since it would be easiest to use it on a mobile robot (compared with hooking it to an external speaker set),
but first I need to verify that the fault is in the speaker and not the electronics (I think I can check that using an oscilloscope).
I finally got around to hunting for a replacement speaker (it is a faulty speaker, the multimeter registers an open between the two speaker terminals), and I scoped the output signal which shows up fine.
21 mm dia speakers are next to impossible to find in my part of the world. I finally managed to find a junked headset which had ~1" dia speakers, at 32 ohms.
By soldering a 33 ohm (nearest value) resistor across the speaker terminals, it gives about 17 ohms, which is 'close enough'.
So now I have sound again, though it is quite tinny (probably because the headset speaker doesn't have much drive), and I can't replace the NXT top cover since the speaker is too large for the enclosure.
I guess I have to keep an eye out for discarded portable speakers/headsets to see if I would be able to find anything closer to 21 mm.
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I purchased the 150 ohm Mylar Cone speakers (took a while for it to be shipped from the UK), and although it fits in the NXT, the sound is barely audible at the max. volume setting and tinny so it's not a 100% replacement. From what I've read elsewhere, those 'speakers' are actually microphones, hence the high impedance.
Actually I think the Mylar speakers are quite fragile. Initially I tried to solder an 18 ohm resistor across the terminals to bring the impedance down to 16 ohms, but upon soldering it to the NXT, the speaker promptly fried and became an open circuit. So for the second attempt (good thing they came in a pack of 5), I just soldered it directly to the NXT with its 150 ohm impedance. Hopefully it'll survive for a while.
I wouldn't normally dig up an old topic, but I figured some people might like to know this. I just found out that the NXT speaker is 8 ohm, and is rated for 0.25 watts (1/4 watt). I measured the diameter of mine to be about 20.5mm. I also noticed a resistor soldered in series, on the PCB. The resistor says "100", so it's 10 ohms.
Here is a picture of the back of the NXT speaker (in a .zip file):
mattallen37 wrote:I wouldn't normally dig up an old topic, but I figured some people might like to know this. I just found out that the NXT speaker is 8 ohm, and is rated for 0.25 watts (1/4 watt). I measured the diameter of mine to be about 20.5mm. I also noticed a resistor soldered in series, on the PCB. The resistor says "100", so it's 10 ohms.
Here is a picture of the back of the NXT speaker (in a .zip file):
NXT Speaker picture.zip
Well, that's good to know. I just got a couple NXTs (YES! I NOW HAVE FOUR!) and I think a couple of them have wonky speakers.
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