If someone has already done this, then I am sorry for bringing it back up. I did not see anything like this in my searches.

I have always found this site very useful for finding odd discrete codes.
When I returned last week to find discrete codes for a Spectrum 101 set top box I was immensely disappointed to find that there were none available. I read thread after thread about how installers were at at their wits-end with customers inadvertently power cycling equipment and leaving the STB out of sync with the power state of the other devices. I too had the same dilemma. My wife would do this over and over. I would watch her eyes glaze over if I tried to explain why this happens.

So I had to put an end to this once and for all. Today I solved this problem with a Arduino Nano, and a single 10k resistor. I piggy-backed off the existing phototransistor in the STB to keep the parts count low. Using this strategy keeps the install simple and does not interfere with the normal remote functions. The Arduino has little power draw and is powered directly from the cable box. In total there are 5 wires:
1) 12 volts ---> Powers Nano from STB; Nano has internal 5v regulator
2) Ground
3) IR receiver/phototransistor ---> Input to Arduino; Collects serial IR data
4) Power LED ---> Input to Arduino; Monitors state of STB power LED
5) Power Button <--- Output from Arduino; Pulses power button when needed

One 10k resistor is used to drag LED line close to zero volts when LED is off.

I did not have to cut any OEM wires or do any other modifications. I just tacked these wires to easily accessible points on a small PCB inside the STB. The Arduino will display the Hex code of any IR command sent to it, if you choose to view it on a PC. I just captured two random hex codes from an old remote I had in a drawer and assigned them to be my discrete On & Off codes. The original toggle power code of the OEM remote still functions as it did before.

Of the 5 wires, the magic is happening with 3 of them. The IR receiver wire passes IR codes from the photo-transistor to the Nano. The Nano checks to see if this is a power request code. If so it will pulse the power button wire. The STB will turn on or off depending on logic checks. The power LED wire is used to verify the state of the box at all times. If the LED is on and a Power On code is sent it ignores it. If the LED is off and a Power On code comes through it will act on it. The same goes for Power Off.

I inherited a very well maintained Phillips Pronto 7500 Color. This will be promptly programmed into that remote, to complete a full Home Theater shut off/on. Of course this could now be done with any decent remote.

I have taken some pics and video. If someone else would like to follow in my foot steps, I will post a video to YouTube with directions.

Thanks