Hacking the Hitachi RAC-EJ10CKM Air Conditioner Remote

 

Hitachi RAC-EJ10CKM and IR Remote

Most of the Internet of Things (IoT, ie smart home) work on new products, new dimmable color LED lightbulbs, new robot vacuum cleaners, cameras, toasters and the like. To get a reasonable degree of intelligence in a smart home requires considerable financial investment. 

And yet there are serious issues that discourage such an outlay. Issues like computer security, reliability (especially those based on WiFi), inter-operability problems, and vendor lock-in. Google products rely on Google servers, and they can fail. Being locked out of your house by a smart lock is extremely annoying. 

Perhaps one way of encouraging IoT adoption is to lower the cost of entry. Most people already have home appliances;  maybe we should retrofit IoT to existing appliances, like smoke detectors, listen for unusual noises like door/window opening, dogs barking and thunder. Or monitor the oven; a 'Hey Google, there's a chicken in the oven' function would be nice. But let us start with the easy ones, some low-hanging fruit, air conditioners.

I have always wanted to automate my air conditioner: it would be nice not to worry about leaving it on by accident. I usually need it for just an hour or two until I fall asleep; it would be nice to have it take an input from a sleep tracking sensor. Or having a passive infrared turn it off when there is nobody in the room. Most air conditioners seem to be controlled from a infrared remote: perhaps I can get an ESP8266 to transmit the control codes. There are quite a few Arduino projects hacking AC remotes, like this one from TaxeIT, whose source code is here. 

Unfortunately my Hitachi seems to be  one of the few exceptions. I could capture the control codes, but the AC stubbornly refused to respond. Yet TaxeIT's method worked well with my Toshiba TV remote. Perhof seems to have an answer: the Hitachi code is simply too long! Perhof uses code from Analysir and my copy (tweaked to use GPIO14) is here. It is nearly the same except for a little tweak for the ESP8266:

void ICACHE_RAM_ATTR rxIR_Interrupt_Handler() {

The resulting capture fires are in my github repository. It helps to check the length of the capture file from each button press:

$awk -F"," '{print NF-1}' AC_On_Raw.txt
530
$awk -F"," '{print NF-1}' AC_Off_Raw.txt
537

This is markedly longer than the files from TaxeIT:

$awk -F"," '{print NF-1}' hitachiACon.txt
98
$awk -F"," '{print NF-1}' hitachiACoff.txt
98

The bigger files have minimum memory requirements, which may be awkward for some CPUs, but fortunately the ESP8266 was more than adequate. Analysir's tutorial has the code to transmit large files. Note the raw capture files have alternating positive and negative numbers, but the transmit code expects all to be positive. This is easy enough to do:

$sed 's/-//g' AC_On_Raw.txt > AC_On.txt

$sed 's/-//g' AC_Off_Raw.txt > AC_Off.txt

And the codes can then be read into the sendRAW_Flash.ino with a little bit of editing. This worked first time if I hold the transmitter no more than 1m away from the Hitachi air conditioner IR remote receiver. Note that throughout, my hardware is still from TaxeIT, reproduced here for convenience:

Image from TaxeIT

Schematic from TaxeIT

There you have it, a proven hack for the Hitachi RAC-EJ10CKM  IR Remote.

Happy Trails.