Replacing Or Improving On The IR Blaster

Many of us have now been forced by Comcast to add a Pace DC50X in front of their MythTV setup in order to record programs in the extended basic tier that used to be broadcast in the clear. IR blasting to control the Pace DC50X works OK with the original MCE USB receiver as it does with the Iguana IR receiver. Sadly, the MCE USB receiver is no longer available and the performance of the Iguana receiver leaves much to be desired so you may be forced by expediency or common sense to use other IR receivers.

The TopSeed IR Receiver works with the on-board USB ports on some motherboards but not others so you can use it, if it is compatible with your motherboard. Its blaster may or may not work with the DC50X. The Pinnacle Systems PCTV Remote seems to work with all on-board USB ports and is readily available. Unfortunately, its IR blaster does not work reliably with the Pace DC50X.

If you are stuck using the Pace DC50X and you need to use one of the IR receivers (like the Pinnacle) whose blaster doesn't work with it, you can try substituting an optocoupler for the combination of the IR blaster supplied with your IR receiver and the IR receiver supplied with the DC50X. Not only is the likelihood of success much greater when an optocoupler is used but the setup looks much neater.

The typical IR blaster output of an IR receiver is a mono 3.5mm jack with the Tip being the Data signal and the Ring being the Ground. If you care to take the DC50X apart, you will see that the "IR IN" jack on the back is electrically connected to the IR detector on the front and, if you care to take the remote IR receiver that comes with the DTA apart, you'll find that the wires leading into it are labeled, and that, according to this labeling, the stereo 3.5mm plug that it uses has power on the Tip, Data on the Center Ring, and Ground on the Base Ring (furthest from the Tip). Or, you can just take our word for it.

To couple the IR blaster output port to the DC50X input port, we will use, as we noted above, an optocoupler to convert the IR blaster's active high signaling to the active low signaling needed on the DTA's input.

Since the basic problem with the Pace DC50X, that we are trying to solve, is that the power output by the IR blaster is not enough to reliably drive the DTA, we want an optocoupler with a high current transfer ratio. The 4N37 (which is an NPN transistor, optocoupler that comes in a 6-pin DIP package) has a CTR of 100 so it should work well. It is also readily available from sources such as Digi-Key for under a buck.

A 3.5mm mono plug is soldered onto a suitable length of flexible, two-conductor wire (if color coded, the red lead should be soldered to the Tip and the black soldered to the Ring). The other end of the wire is carefully soldered to pin 1 (Tip) and pin 2 (Ring) of the optocoupler. A couple of bits of shrink tubing can make the job neat and prevent short circuits.

A 3.5mm stereo plug is soldered onto another suitable length of flexible, two-conductor wire (if color coded, the red lead should be soldered to the First Ring and the black soldered to the Second Ring). The other end of the wire is, likewise, carefully soldered to pin 5 (First Ring) and pin 4 (Second Ring) of the optocoupler. More shrink tubing can be applied for insulation, including a larger piece over the optocoupler itself. Note that the DTA power, from the stereo plug's tip, is not connected.

When you plug the mono jack into the IR receiver and the stereo jack into the DTA (now's a good time to label them), control of the DTA should prove much more reliable.