Recently I discovered that our local cable provider will soon be discontinuing analog cable service for most channels.   Because of this they are forcing encouraging customers to get new cable boxes and upgrade to digital cable.

I hate cable boxes.  More than just another piece of equipment to find a place for near the television, cable boxes waste power, always seem to take forever to change channels, contribute to the ball of wires behind the entertainment center, and add another remote control to the coffee table.

Most importantly, a cable box prevents our old Series 2 TiVo from being able to change channels directly, since it now has to negotiate with the digital cable box to receive TV signals.

TiVo provides a workaround for this – the infamous IR blaster.

I would love to meet the engineer who came up with the IR blaster.  Instead of pushing for a universal protocol to electrically connect cable boxes to things that may want to control them, some engineer came up with the incredibly stupid great idea to stick an IR LED in front of the IR receiver of the cable box and use it to simulate a handheld IR remote control.  The cable box thinks that the user is punching away at the remote (with lightning speed) while in reality a microprocessor is generating the remote codes and sending them to the LED.  It’s both ingenious, and at the same horrific in so many ways.  It grates against my engineering sensibility.  What manager approved this?

Back to the TiVo.  The IR blaster that came with our TiVo was lost long ago, in a time when no unnecessary electrical-optical-electrical sillyness was required for it to function.  Rather than spend $3 on eBay and wait a week to get a replacement, I decided to make one out of spare parts in my junk bin:

• an infrared (IR) LED
• a 1k resistor (not sure if this is necessary, safety first)
• a 1/8″ mono headphone plug with a couple feet of cable attached
• some heatshrink tubing
• duct tape

I don’t know if the resistor is required – the TiVo may already have an internal resistor.  I used 1k, if I see any problems with the cable box getting an intermittent signal I’ll try lowering the resistor to 330 ohms.

The tip of the 1/8″ mono plug is positive.  I connected the tip wire to the side of the LED with the longer lead (the side opposite the flat side of the LED).

I tested the circuit by applying 3-5V to the 1/8″ plug (tip is positive) and used my digital camera to check if the LED is working.  My camera has a decent IR blocking filter so I had to use nightshot mode to see it:

Finally, I put heatshrink over the LED connections and the resistor to avoid short circuits:

Back in the living room I plugged the DIY IR blaster into the jack marked ‘IR’ on the back of my TiVo.   A strip of duct tape to secures the wires to the bottom of the cable box.  I bent the LED up to point at the cable box’s IR receiver (the purple dot shown in the really bad photo below, sorry).

All that was left was to configure the TiVo using the cable box setup guide.  Within a few minutes I had my TiVo controlling the cable box.  The DIY IR blaster works perfectly!

Not bad for $0 in parts (all stuff from my junk bin) and a few minutes of soldering.

Update November 2016: In the vast majority of applications, the series resistor is not required. The majority of IR blaster circuits built into A/V equipment (and video game consoles such as the Xbox) include built-in current limiting circuitry that makes the resistor unnecessary.