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TOPIC: Using 5V instead of GND for speaker

Using 5V instead of GND for speaker 5 years 6 months ago #324

Hi,

I am using ginsing in quite a complicated setup that includes all the digital outputs of my arduino uno in use, and two separate sytems (arduino on one end, sensors/actuator on other end) that are connected by a 10-wire cable. Anyway, the point is that I have only limited channels available and need be as economical as possible.

I found that if you look at the ginsing from the top with the speaker holes on the right-hand side, that the lower hole is connected to GND, and the upper hole driving the information. Now for my application it would be easier if I could feed the speaker a clean 5V, and drive the information through GND. I tried simply connecting a speaker to the upper hole (information) and to 5V, expecting to hear sound but at a diminished level. To my surprise it sounded exactly the same as in the intended setup. Only thing that was different is that the Ginsing LED is reacting a bit to the light - when it gets louder the LED shines a bit brighter.

My question is, is it harmful to use a setup this way? And would I be able to build a small circuit to compensate?

Hope all of this makes a bit of sense, if not I can clarify some more.

Thanks,
Steven
Last Edit: 5 years 3 months ago by administrator.
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Re: Using 5V instead of GND for speaker 5 years 6 months ago #325

Hi Steven. I don't think you would do any damage to the circuit by running the speaker to Vcc rather than ground because the output IC uses a push-pull output and a coupling capacitor to drop off any DC bias. Here is a simple schematic of the NJM386 IC :



From this you can see that Vout (the speaker pin ) floats between +5V and ground, although there is some minor bias variations caused by the slight difference in upper vs. lower asymmetry. The large 220uF capacitor on the shield blocks any DC bias that you would normally see ( i.e. ~2.5V ) so it should be fine to go either way w/r to Vout.

The LED output is actually a PWM digital output fed from the Babblebot IC ( PIC18F ), and in theory should not be effected by the output circuit; I find it strange that it behaves differently but since its current limited I can't see how it would suffer from simply taking speaker output between Vout and Vcc.
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Re: Using 5V instead of GND for speaker 5 years 5 months ago #326

Thanks, that makes it a lot easier for my application!
Yes, strange thing about the LED, but the effect is very nuanced. I could try to make a video of it later.
By the way, is there a way to temporarily (non-destructively) disable the LED?
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Re: Using 5V instead of GND for speaker 5 years 5 months ago #327

The output on the LED is set by the micrcoode running on the Babblebot, so it can't be disabled through code. However, you can heat up the contacts on the LED ( or resistor ) with a soldering iron and just pull it off the board; should not require too much grief. You may elect to remove the Babblebot IC proir to heating the board just to be safe. Of course, there is always electrical tape as well.
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