The Other Kind of Phone Hacking

While it’s true that your parts bin might have a few parts harvested from outdated devices of recent vintage, there’s not much to glean anymore aside from wall warts. But the 3×48-character LCD from [Kerry Wong]’s old Uniden cordless landline phone was tempting enough for him to attempt a teardown and reverse engineering, and the results were instructive.

No data sheet? No problem. [Kerry] couldn’t find anything out about the nicely backlit display, so onto the logic analyzer it went. With only eight leads from the main board to the display module, it wasn’t likely to be a parallel protocol, and the video below shows that to be the case. A little fiddling with the parameters showed the protocol was Serial Peripheral Interface, but as with other standards that aren’t exactly standardized, [Kerry] was left with enough ambiguity to make the analysis interesting. Despite a mysterious header of 39 characters, he was able in the end to drive the LCD with an Arduino, and given that these phones were usually sold as a bundle with a base and several handsets, he ought to have a nice collection of displays for the parts bin.

With how prevalent this protocol has gotten, [Kerry]’s post makes us want to get up to speed on the basics of SPI. And to buy a logic analyzer too.

5 thoughts on “The Other Kind of Phone Hacking

  1. Good work!
    I had a similar challenge once, but the display was soldered
    to the board through a fine pitch flex cable.
    Thankfully the board used a atmega328, so I was able to figure
    out the pins and model by disassembling the firmware.
    Only to later find the pins listed on a forum.

  2. Don’t have a Uniden (poor quality stuff) but I haven’t taken any of the cordless apart, because they still work, and I still haven’t forgotten how much those buggers cost apiece.

  3. Good video explaining the process.
    I have the same phones here but I just got new batteries for them. I like these phones.
    One of them I added an audio isolating transformer to give mic audio out so my daughter can use it for phone patch on her radio show. It can be plugged in to a USB audio i/p box and then she can record mic and speaker audio on separate channels for editing.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s