Monday, October 17, 2005

The Pioneer SR Control In/Out Jacks

There is a pair of 3.5 mm jacks on the back of my Pioneer receiver. One is a "control in" jack, and the other is a "control out". My Pioneer DVD player also has a "control in" jack.

The idea is that you can link all your Pioneer equipment together so that they can control each other. If I connect the receiver's "control out" jack to my DVD player's "control in" jack, the DVD player responds to remote contol signals via the "control in" jack instead of via its built-in IR sensor. This is especially cool when the controlling unit and the controlled unit are in different rooms. It's like a wired version of an IR repeater system. Plugging into a control jack on the back of the unit is a lot cleaner than sticking an IR emitter to the front of your equipment.

Control Jack Electrical Interface

To find out what kind of circuit was on the other side of the recever's "control out" jack, I plugged a 3.5 mm mono plug into the jack and hooked it up to an oscilloscope. There was about five volts of output on the tip line when it was idle. I pointed a remote at the receiver and pressed a button. I saw a train of zero volt pulses, which look a lot like what comes out of those Sharp IR receiver modules. Those modules have an open collector output and a pull-up resistor. I suspected that the control jack was the same. To find out, I attached a pull-down resistor between the control out jack and ground. The control jack's voltage went down. I found that with a 10K pull-down resistor, the "control out" voltage was about half of its normal five volts, so I know that the internal pull-up resistor was the same. I also found that the internal pull-up resistor for the "control in" jack was around 100K.

Interestingly enough, it doesn't look like the outer ring of the control jacks are grounded. I had to find a ground somewhere else on the receiver, like one of the RCA jacks.

Control Jack Protocol

I suspected that the control signal was just a demodulated version of the IR signal coming from the remote. To prove it, I hooked channel one of my scope to the tip line of the "control out" jack and channel two of the scope to the output of a Sharp IR receiver module. I pointed a remote at both units and pressed a button. Both channel one and channel two showed the same signal. I also found that the "control out" jack repeats the signal from any remote I pointed at the unit, not just my Pioneer remote. This is all very good news.

The Mitsubishi VCR

I have a Mitsubishi HS-U447 VCR that has no control jacks at all. I figured that all I needed to do to add a jack would be to wire a closed-circuit type of 3.5 mm mono jack in series with the built-in IR sensor. I opened up the VCR and found the sensor. It had the usual three leads. A volt meter showed one lead at zero volts, and the other two were around five volts. So, one of the five volt leads was the output, which is normally high. The scope showed me which one it was. Also, the volt meter, when set to AC volts, showed me an AC voltage on the output when I pressed a button on the remote.

After some probing around with an ohm meter, I found that the output of the IR sensor went to a nearby resistor. I cut one lead of the resistor and connected the 3.5 mm closed-circuit type jack in series with the sensor's output and the resistor. The jack is wired in such a way where the IR sensor will be connected to the resistor if nothing is plugged in. If something is plugged in, then the tip of the plug will be connected to the resistor, and the IR sensor will be disconnected.

Here are the wires soldered onto the sensor output, the resistor, and a ground point.

As for where to put the jack, I found a convenient spot on the back of the VCR and drilled a hole just large enough for the jack. Fortunately, the back panel of the VCR was plastic, so it was easy to drill.

Testing The New "Control In" Jack

First, I plugged nothing into the jack and used the remote with the VCR to make sure it still worked. Next, I plugged one end of a cable into the new jack and left the other end of the cable unattached to anything. I tried the remote again and made sure that it didn't work anymore, since the plugged-in cable should be overriding the internal IR sensor. And last, I plugged the other end of the cable into the Pioneer receiver's "control out" jack and tried the remote again, this time pointing it at the receiver. All worked well. Keep in mind that since the ring of the receiver's "control out" jack isn't grounded, you have to ground the VCR to the receiver another way, like with the video and audio cables.

And now, two pieces of AV equipment which were never meant to be attached are playing well together.

The JVC DVD Player

I also have a JVC DVD player that could use a "control in" jack too. This player is very new, and I don't feel like drilling holes in its metal case to add a 3.5mm jack. I might change my mind in a year or so, but not today. I took it apart and looked at it for a while, and then I got an idea...

Now, when I start telling you about this, you're probably going to think, "John, you're an idoit. You're going to blow up your equipment." But, think about it for a while first. If you still think I'm an idiot, just send me email and tell me why. Perhaps there's something I haven't thought of.

This DVD player has two 3.5mm jacks on the back already for AV CompuLink. I already checked, and it looks like the CompuLink protocol is not an unmodulated version of the IR signal. Too bad. But, both the CompuLink signal and the IR sensor signal look like they both have the usual open collector output. Hmm, I could just wire the IR sensor output and the CompuLink jack together. Yeah, the CompuLink input will be getting the IR signal, and yeah, the IR input will be getting the CompuLink signal, but I'm hoping that each input ignores signals that it doesn't understand. Of course, wiring it up this way will cause the jack to be not only a "control in" jack, but also a "control out" jack. Whatever signal the internal IR sensor picks up will be sent out the jack. I'll just have to keep this in mind. It might even be useful in the future.

So, here's the board that has the IR sensor, as well as some of the front panel buttons.

I unscrewed the board and looked at the other side. You can see the IR sensor. You can also see that there is an extra set of holes for what might be a different kind of sensor that's not used. I found the hole that's connected to the sensor's output and soldered a wire to it.

I then soldered the other end of the wire to the CompuLink jack's tip connection. That's it. I'm done. No parts were cut, and no new holes in the case were drilled.

Testing The "Control In/Out" Jack

I tested this one pretty much the same way I tested the Mitsubishi VCR by hooking it up to my Pioneer receiver's "control out" jack. I also tested both the DVD player and the VCR together by connecting their control jacks together. I could control the VCR by going through the DVD player's IR sensor, out its control jack, and into the VCR's control jack.

Right now, these two guys are hooked up a pair of modulators which are distributed to all the TVs in the house. Also, near each one of the TVs is an IR sensor that's wired into a control bus, which is connected to both of these units. I can control the VCR or the DVD players from any room with a TV. It seems to work great, and I haven't blown anything up... yet.

Naming These Jacks

These remote control jacks behave differently depending on how they are wired. It would be nice if I labeled them so that I know what kind of jacks they are. Since I don't know of any standard naming method, I'll make up my own. I'll prefix the name with RC- for remote control. Then there will be one or more qualifiers which will tell you what kind of remote control jack it is. I'll use these:
  • I - Jack accepts remote control commands as input
  • O - Jack outputs remote control commands
  • X - Plugging into this jack disables the internal IR receiver

There are only several combinations that even make sense, and I'll give you two examples of the ones I think are most useful. The first is the RC-IX jack. It will accept remote control commands as input. It does not work as an output. Plugging into this jack disables the internal IR sensor. It is wired like this:

Another one that is easy to implement is the RC-IO jack. It allows the unit to accept commands via this jack. Also, any IR commands that get picked up by the unit's internal IR sensor get sent out this jack. It is wired like this:

So, when would you want to use an RC-IO jack? Well, I can think of one use, and that's when you would combine it with an RC-IX jack, like this:

So, you could have your control line going into the RC-IX jack on one unit. Then, if you want to control a second unit, you would plug in a cable between unit one's RC-IO jack into unit two's RC-IX jack.

The wiring for an RC-I jacks is a little trickier, because you want to accept input, but have no output, and you don't want to disable the internal IR sensor. You would need some sort of buffer to allow the signal to pass only one way. The same is true for RC-O jacks. Maybe a simple diode would work. I'll leave that up to you.