With the exception of the commands to toggle the energy saver feature and the front panel lights, all of the commands encode a full system state instead of just a single command, ensuring the remote stays in sync with the air conditioner. This state is encoded in five bytes containing information on the power state, sleep state, system mode, fan speed, set temperature, and the remote temperature sensor reading. The final byte is some sort of checksum, which I have not been able to figure out. The remote is based around a 4-bit microcontroller with 64 bytes of RAM, a Sino Wealth SH66P51A, so the checksum calculation must be something simple. Based on its behavior to changing input, it seems to involve XOR operations, but it does not always behave like a simple XOR. As I haven’t been able to figure out the functional form of the checksum calculation, I can only send commands that I have recorded from the remote. This isn’t too much of an issue as I recorded all of the possible commands except for those involving the remote temperature sensor feature (and the timer since I didn’t care about it). Recording all temperature sensor commands would be very difficult as it only transmits once every three minutes and one needs to get the sensor to report all values. I was hoping to emulate the remote’s temperature sensor using a higher quality sensor, but, alas, I can’t without the functional form of the checksum. It turns out that the bit order of the data needs to be reversed for the checksum calculation. The checksum can be calculated by reversing the bit order of the five data bytes; adding them, truncating the result to 8 bits, and subtracting the result from 2⁸; and reversing the bit order of the subtracted result. Below is a Python function to do the checksum calculation.

def calc_checksum(bytes):
    # Reverse bits for each bytes
    bit_reversal = []
    for i in bytes:
        bit_reversal.append(int('{:08b}'.format(i)[::-1], 2))
    # Calculate checksum
    checksum = 2**8 - sum(bit_reversal) % 2**8
    # Return bits to original order
    return int('{:08b}'.format(checksum)[::-1], 2)

Detailed information on the individual data bytes, values recorded from the remote, and Python code for emulating the remote with a USB Infrared Toy is available here. If anyone figures out the checksum calculation, please let me know.

Edit 2016-04-23: Tim Chang figured out the checksum calculation and let me know via email. I updated the post to include the checksum calculation.

Edit 2016-08-17: Fixed description of middle pulse.

Also on Vimeo.

All of the following photos can be enlarged if clicked. Sample images from the modified camera are at the end of the post.

Disassembly:

To get started, one needs a #000 Phillips screwdriver; in addition, pointed tweezers are quite helpful. The camera is a delicate piece of electronics and optics that is easily damaged and also contains, while shielded, a dangerous high voltage flash system. Proceed at your own risk.

Before beginning, remove the battery and let the camera sit so that the flash capacitor discharges.

Camera Front

Camera Back

First, remove the six outside screws.

First Pair of Screws

Second Pair of Screws

Last Pair of Screws

Next, open the case while being careful not to bend the metal.

Opening the Case

The buttons, the strap connector, and the seal around the lens will fall off.

Strap Attachment

Buttons

Then, disconnect the screen’s ribbon cable on the front of the camera by lifting the latch on the socket and gently pulling on the cable.

Screen Ribbon Connector

Now, remove the screw at the upper-right corner of the screen (it’s a different size). Next, pop the clip to the left of the screen, move the screen slightly toward the viewfinder to free the tab on bottom-right corner, and lift the left of the screen, folding it toward the right like a book page while feeding the ribbon cable through from the front of the camera. Be mindful of the remaining cable connected to the right side of the screen.

Screen Removal

Next, disconnect the back-light to free the screen and then unscrew the image sensor. There are three springs behind the image sensor to watch for and then remove.

Back of Image Sensor

Then, fasten sensor out of the way, thread works well, and remove the square rubber gasket below it. Avoid touching the sensor.

Sensor Removed

The piece of glass that is below where the sensor was is the infrared cut-off filter. It is glued down. Carefully pry it off (it will likely break, but we don’t want it anyway). Be sure all fragments and debris are removed.

Infrared Cut-off Filter

Visible Light Cut-off Filter:

One now has the option of replacing the infrared cut-off filter with a visible light cut-off filter. For this, fully exposed and then developed film negative works well. Take a roll of film, pull the film out of the roll in a lit area, re-roll it, and take it to be developed. Be sure to ask for no prints, only the negatives, and make it clear that you know the film is fully exposed but want it developed anyway. Four layers of developed film worked well for me to block most visible light. Cut the negative into rectangles the same size as the infrared cut-off filter was, 9.0mm wide by 8.0mm tall. If the film is curling, briefly iron it between sheets of paper on low heat to flatten it. When cutting out the rectangles, it helps to print the correct sized rectangles on a piece of paper without scaling, tape the negative to the paper, and precisely cut out the printed rectangles with the film behind it.

Cutting Negatives

Negative Rectangles

Next, carefully place the pieces of negative where the infrared cut-off filter was and glue them in place; I used white glue on a toothpick. Wait for the glue to dry.

Installed Negatives

Reassembly:

To reassemble the camera, first replace the square rubber gasket above the former location of the infrared cut-off filter. Next, replace the three springs and screw the image sensor back in place. One might have to go back and adjust the height of the image sensor to fix focus issues that may result from modifying the optical path. Replace the screen by first reconnecting the back-light cable and feeding the larger ribbon cable back to the front of the camera. It helps to feed a thread through the camera, tie it to the end of the ribbon cable, and pull the cable through that way. Note that the ribbon cable should be over, not under, the red and black wires on the back of the camera. Insert the tab on the lower-right corner of the screen into the appropriate slot, click the tab on the left side back into place, and replace the screw at the top-right corner of the screen. Turn the camera over and reconnect the ribbon cable. Then, replace the buttons, the gasket around the lens, and the strap connector, and replace the case and its six screws. Enjoy your infrared sensitive camera!

Sample Images:

Two photos were taken at the same location. The left half is visible light from an unmodified camera; the right half is infrared from the modified camera (with visible light cut-off filter).

Now, more sample infrared photographs.