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View Full Version : How to connect a 8-Ohm speaker to the BS-2?



nboucquey
04-29-2006, 03:17 AM
I have to connect a 8-Ohm Speaker to my BS-2. How?

Can I connect it directly or via a transistor?

Thanks.

Nicolas

Chris Savage
04-29-2006, 03:21 AM
Hello,

·· There is an example schematic for this right in the Editor Help File under the FREQOUT command.


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Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)

Paul Baker
04-29-2006, 03:30 AM
When I just saw your thread topic I was going to jokingly reply to directly connect it, but after reading your post I want to emphasize that is not what you want to do, neither will a transistor really work for driving the speaker. You need something more complex if you want to be able to play a variety of sounds, check out this http://www.parallax.com/dl/docs/prod/boards/PDBSchem.pdf#page=3. This is the schematic for the speaker on the Professional development board, so it will work.

Or follow Chris' advice since it will likely be a simpler circuit to construct.

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1+1=10

sam_sam_sam
04-29-2006, 05:01 AM
Hi EveryOne

In this schematic It dose not put a # to this chip
Can any one tell me what chip was used in this link below

http://www.parallax.com/dl/docs/prod/boards/PDBSchem.pdf#page=3.
This is the schematic It dose not put a chip #

I want to built this circuit

Thanks to any one that can help with this

Sam

Paul Baker
04-29-2006, 09:04 PM
Nearly any op amp would work, but the chip used on the PDB is LM386.

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1+1=10

PJ Allen
04-29-2006, 10:04 PM
Pity that we've forgotten, or relegated to obscurity, our old friend -- the audio output transformer (still available at Radio Shack.)

Post Edited (PJ Allen) : 4/29/2006 3:18:46 PM GMT

Loopy Byteloose
04-29-2006, 10:34 PM
For anyone that is lurking, 8 ohm or 4 ohm or even 16 ohm speakers are a 'no, no!' The same goes for any transformer in that range.

Consider Ohms law ([E=IxR] 5volts / .025 amps = 200 ohms) and you will see why people are suggesting 220ohm resistors as protection for the Stamp.

Anything much lower will burn out the I/O pins.

Thus, the handy LM386 is recommended. Is that the handy little 5 watt audio amp chip?

If you just want to get sound, a transistor or a darlington might do the trick too.

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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

·················································· ···················· Warm regards,····· G. Herzog [·黃鶴 ]·in Taiwan

PJ Allen
04-29-2006, 10:40 PM
I wasn't advocating a transformer to the STAMP output (but I'll have a think on it), rather using a transistor, of course part of the WAM kit, and a couple of resistors, along with the audio output transformer (1k:8).· All this stuff where nothing·is any good·if it ain't an IC is tiresome.· I was hoping someone might figure, "hey, audio transformer, what's that?"

Paul Baker
04-29-2006, 10:49 PM
I actually have a PA transfromer from RadioShack, multi-tap to provide the proper coupling given the amplifier's power and speaker's ohmage.

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1+1=10

PJ Allen
04-30-2006, 02:44 AM
· OK -- proof positive.· I am getting good volume from a circuit using an audio transformer.· As a matter of fact, it's running right now and driving me to distraction.
· It's a 1kohm:8ohm audio transformer.· The only other components needed are a 10uF cap and a 330ohm resistor.· I'm using a HomeWork Board, which has the built-in 220ohm resistors on the I/O.· If that's not your situation, use a 470ohm instead of the 330ohm.
· Drawing/schematic attached.


**** Post Edit ****

· My nearest Radio Shack still stocks·the "miniature audio output transformer", #276-1380 273-1380.· [N.B. -- Don't buy the other one, the 1:1,·it's for something else.]
· Also, they've had outstanding pricing (I think) on 'AA' & 'AAA' batteries·selling·40-packs for $19.99 [that's 50c each].· Well, they've made it even better, those same 40-packs are now $16.99 [that's 43c each]!!!· The packs I bought are dated for 2010 (so it's·not like a sale on lunch-meat.)·
· Zip-Zaps are Clearance Priced, too -- $12.47.

Post Edited (PJ Allen) : 4/30/2006 4:08:54 PM GMT

sam_sam_sam
04-30-2006, 07:37 AM
·Hi Paul Baker (http://forums.parallax.com/member.php?u=40916)

Thanks for your reply

Sam

·

sam_sam_sam
04-30-2006, 07:54 AM
·Hi PJ Allen (http://forums.parallax.com/member.php?u=44113)

Thanks for posting this

Pity that we've forgotten, or relegated to obscurity, our old friend -- the audio output transformer (still available at Radio Shack.)· audio_xfmr.jpg · 44KB (image/pjpeg)

That just what i was looking for

Sam





Post Edited (sam_sam_sam) : 4/30/2006 12:57:02 AM GMT

SSteve
04-30-2006, 12:07 PM
PJ Allen said...
My nearest Radio Shack still stocks the "miniature audio output transformer", #276-1380

I believe you meant 273-1380 (http://www.radioshack.com/product/index.jsp?productId=2103254). Unless they've changed numbering and you're looking at some old stock.

Thanks for pointing that out. As a newcomer to the hardware side of things it's good to hear about other ways to do things. Especially when they are cheap enough to experiment with just for the fun of it.

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OS-X: because making Unix user-friendly was easier than debugging Windows

Loopy Byteloose
04-30-2006, 06:27 PM
Actally, the part count with the transformer is minimal. And I really like that even if others may say the sound quality is not as good [not much wattage].

Just to re-emphasize the problem. Don't EVER put the 8 ohm side of the transformer to the BasicStamp. That 220 ohm resistor may be there to save you on the Homework board, but not in all situations.

Everything under 200 ohms should be questioned.
Everything over 25ma should be questioned.

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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

·················································· ···················· Warm regards,····· G. Herzog [·黃鶴 ]·in Taiwan

PJ Allen
04-30-2006, 08:42 PM
SSteve -- Yes, you're right, it is 273-1380.· It's me tired old eyes (presbyopia & astigmatism); I'm getting on, now, y'know.

Kramer -- You're right, nobody·better put an 8ohm speaker directly to the output ("double-plus un-good" ).

· The PBASIC Help shows one way to use a speaker.· They use a 47ohm resistor in series with an 8ohm speaker.· I can tell you that using the transformer,·however imperfect,·results a lot more volume at the speaker, because it doesn't·have nearly·all the output across the non-transducing resistor (as in the PBASIC resistor-speaker configuration.)

· nboucquey wanted to know of some way to do this.· I assumed it was for tones, alarms, beeping purposes (and for such I reckon this is a winner.)

Loopy Byteloose
05-01-2006, 08:17 PM
I went shopping today and came across a 400 ohm to 8 ohm transformer. [Not at a Radio Shack, they don't exist in Taiwan]
I suppose that can squeeze about as much volume as possilble out of a BasicStamp without an amplifier.

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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

·················································· ···················· Warm regards,····· G. Herzog [·黃鶴 ]·in Taiwan