Too high voltage for sound card ? - Question for Sanjay about his design.

[Julian]

Sanjay,

I write from Spain and some days ago I bough all items to make the cable you propose to connect a Futaba SkySport4 to my PC sound card (This PC is running XP). However, I´ve got a question and I don´t find the answer by myself. I was told that voltage input levels applied either "line-in" or "microphone" sockets should be low (in general, lower than 1 volt) and apparently, as mentioned in FMS manual, the output level of the transmitter buddy socket could reach in Futaba up to 11 volts. I´m not an expert in electronics but the cable design you propose just puts the same voltage from the transmitter to the sound card, this is, up to 11 volts. Don´t you think this could damage the sound card ?. Shouldn´t we use a voltage divisor to reduce the sound card input voltage ?.

I would appreciate very much if you could clarify this doubt for me and may be for some others.

Thanks in advance.

Regards,

Julian,

[sanjay]

The sound card interface is a design from Tsutomu Seki.



I was just copying the link into the forum to answer a question on possible interfaces.

The Futaba wiring diagram does require a resistor as shown in the diagram.

Regarding the voltages you should contact Tustomu directly for further advice since he is the creator of this interface and the software.

[Julian]

Thanks Sanjay,

I´ve already contacted Tsutomu and he´s gonna give an answer soon. Then, I´ll post the reply for all users.

Julian,

[Pooky]

I have a question about this interface. Do you have to use a mono jack for the soundcard or can you use a stereo jack instead? I built the cable but unfortunatly my pc has 2 mic inputs and 3 line-in inputs and its a bit confusing trying to figure out which one to use. Im using a Soundblaster Audigy Platinum soundcard you see, and my Via onboard sound is also enabled.... Also is it safe connecting a TX to the soundcard. If anyone has any views about this i would be most appreciative.

Pooky.

[mritchie]

I used a mono plug on my lead from my JR 3810 with no resistor. A stereo jack should work ok, only the signal will be presented to the left or right side I/P, depending on which tip contact you wire to in the plug. If you have problem using the middle contact on the stereo plug, you can always change it to the tip, ie. mono configuration and this will work ok. Do be cautious of the voltage level before connecting to your PC - straight connect from the JR works ok. In fact I had to use the MIC I/P and boost the gain to about 90% to get it to work on my sound card.

As for which input to use, I would start with one of the LINE inputs which have a lower gain and can tolerate a slightly higher voltage level. Pick a port and plug in either a sound source (ie tape or cd player) or your transmitter and listen for the sound, then adjust the gain level control in windows - open the “Master Volume Control” by double clicking on the little speaker down near the clock. If your input is not displayed, go into Options…Properties… and tick on the INPUT channels you want to use.

If your still uncertain or worried, plug a "cheap" sound board into your PC and test on that first. Here is Aust. "cheap" sound boards can be found for about $10 at some of the markets, so not a great expense really.

[Pooky]

Cheers mritchie, everythings working now.

Pook. :p

[Julian]

:p Hi,

So far, I haven´t received response from Tsutomu and I´ve decided to implement a two wire cable with and simple variable resistor built in (serial built in). This resistor goes up to 2.2 Mohms and the design works fine. The best sensibility I´ve seen is when the resistor is at mid range, this is, around 1 - 1.2 Mohms. The jack connector is put at the line-in socket. And my sound board is still up and running.

If I receive news from Tsutomu, I´ll post them.

Cheers.

Julián,