Adam Novagen
- Dec 7, 2012
- 3
- Joined
- Dec 7, 2012
- Messages
- 3
Hello all!
I think this is the right forum for this question, and a quick search to see if my question had been resolved in years gone by revealed nothing, so here goes.
I'm doing a little hobby project, which I call the Mega Pi. I'm installing a Raspberry Pi inside the shell of an old SEGA Genesis (Mega Drive). The model 1, in case you're wondering. Rather than simply stick the Pi inside the plastic case, though, I decided to fiddle around with the Genesis' board and see what I could do to make the unit look and feel as much like the original as possible. So far, I have successfully hijacked the original power switch, power input (the R-Pi is powered via microUSB but a quick cable splicing solved that), power LED, and converted the RF output jack to work as the composite video output. I'm now working on the headphone jack, though, and here's where I've hit a slight hiccup.
For those of you that don't remember or know, the model 1 Genesis had a stereo headphone jack and a lovely potentiometer-controlled volume slider on the console itself, which I intend to put to use. The initial splicing went perfectly, the headphone jack is fully operational as normal with no issues. The volume slider, however, is another story. At first glance, it appears to have six leads connecting it to the motherboard, or two pairs of three. Okay, I thought, left, right, ground. Standard headphone setup, no biggie. After some significant soldering and testing, however, I discovered that four of the six leads are in fact dummies, serving only to anchour the potentiometer to the board; only one pair is actually operational. Alright, I thought, no big deal; I'll just do the obvious, and connect the headphone ground cable to the one active slider, thereby controlling the volume of both channels at once. I quickly discovered it wasn't that simple.
The connection works perfectly, and acts as it should; however, when I turned the volume down (via the slider), I noticed a strange phenomena. The sound changed; it didn't exactly fade per se, but rather became thinner and distant. I also noticed that certain parts of the music I was using to test the connection stayed perfectly audible, while others disappeared. That's when I realized what was obviously happening.
The sounds that were disappearing were the more "centred" sounds, the ones that would require both channels to carry the same level of voltage at the same time. I realized that since I had "lowered the volume" by increasing the resistance on the ground line, the left and right channels had simply formed a circuit with each other; that is to say, a mono sound producing the same waveform in both channels at once would simply cancel itself out, while sounds that were different between the two channels would actually "rock" back and forth between them. A kind of two-way mono circuit, if you will.
The solution seems obvious: diodes. One diode on both the left and the right channel, so that they can no longer "bleed through" each other in this way. The thing is, while I'm great at the theory of circuit logic and electrical flow, I have no actual training in what really makes electronics tick, so I have no idea what diodes I'd need for this - volts, amps, frequency etc, I don't even know what terms to use - or even if this idea would actually work.
So that's the situation. Sorry for the long post, but I wanted to make sure I provided enough information; any advice?
I think this is the right forum for this question, and a quick search to see if my question had been resolved in years gone by revealed nothing, so here goes.
I'm doing a little hobby project, which I call the Mega Pi. I'm installing a Raspberry Pi inside the shell of an old SEGA Genesis (Mega Drive). The model 1, in case you're wondering. Rather than simply stick the Pi inside the plastic case, though, I decided to fiddle around with the Genesis' board and see what I could do to make the unit look and feel as much like the original as possible. So far, I have successfully hijacked the original power switch, power input (the R-Pi is powered via microUSB but a quick cable splicing solved that), power LED, and converted the RF output jack to work as the composite video output. I'm now working on the headphone jack, though, and here's where I've hit a slight hiccup.
For those of you that don't remember or know, the model 1 Genesis had a stereo headphone jack and a lovely potentiometer-controlled volume slider on the console itself, which I intend to put to use. The initial splicing went perfectly, the headphone jack is fully operational as normal with no issues. The volume slider, however, is another story. At first glance, it appears to have six leads connecting it to the motherboard, or two pairs of three. Okay, I thought, left, right, ground. Standard headphone setup, no biggie. After some significant soldering and testing, however, I discovered that four of the six leads are in fact dummies, serving only to anchour the potentiometer to the board; only one pair is actually operational. Alright, I thought, no big deal; I'll just do the obvious, and connect the headphone ground cable to the one active slider, thereby controlling the volume of both channels at once. I quickly discovered it wasn't that simple.
The connection works perfectly, and acts as it should; however, when I turned the volume down (via the slider), I noticed a strange phenomena. The sound changed; it didn't exactly fade per se, but rather became thinner and distant. I also noticed that certain parts of the music I was using to test the connection stayed perfectly audible, while others disappeared. That's when I realized what was obviously happening.
The sounds that were disappearing were the more "centred" sounds, the ones that would require both channels to carry the same level of voltage at the same time. I realized that since I had "lowered the volume" by increasing the resistance on the ground line, the left and right channels had simply formed a circuit with each other; that is to say, a mono sound producing the same waveform in both channels at once would simply cancel itself out, while sounds that were different between the two channels would actually "rock" back and forth between them. A kind of two-way mono circuit, if you will.
The solution seems obvious: diodes. One diode on both the left and the right channel, so that they can no longer "bleed through" each other in this way. The thing is, while I'm great at the theory of circuit logic and electrical flow, I have no actual training in what really makes electronics tick, so I have no idea what diodes I'd need for this - volts, amps, frequency etc, I don't even know what terms to use - or even if this idea would actually work.
So that's the situation. Sorry for the long post, but I wanted to make sure I provided enough information; any advice?