BT Decor telephone - Making improvements

[steve30]

I bought a new telephone the other day; a BT Decor 2200, for about £25.

Its quite a nice unit, it has nice clear sound, looks good, has a handset which is nice to hold, and has big buttons.

However, it has a few niggles. The LCD is rather hard to read. It has little contrast, despite the setting, and some of the buttons (particularly the menu and phonebook buttons) aren't very responsive. Firstly, here's a few teardown photos:

The first attachment shows the keypad PCB with carbon pads.
The second attachment shows the LCD at a typical angle, and is quite hard to read. I think it actually shows up better on the camera than it does in real life.
The third attachment shows the LCD at a good angle. Again, it looks better on camera.

I'm wondering what causes some of the buttons to be a bit unresponsive. I put some conductive ink on the keypad plastic (rubber?), but that didn't make much difference. I'm also not sure what makes the LCD a bit crappy. I might be able to hack a backlight in there, as there is plenty of room.

Any thoughts or opinions are welcome. These are only minor problems, and aren't of great importance, but being an electronic hobbiest, I do like to try and improve these things if I can .

[SeanB]

Probably a very low clock speed on the micro which makes it slow to respond to keypresses, but saves power. Look to see if there is a negative voltage bias generator that you can vary the voltage of to improve contrast range. Cheap unit, only one quality PCB with the display, and a cheap one for the keypad and an even cheaper one for the phone side.

[steve30]

Probably a very low clock speed on the micro which makes it slow to respond to keypresses, but saves power. Look to see if there is a negative voltage bias generator that you can vary the voltage of to improve contrast range. Cheap unit, only one quality PCB with the display, and a cheap one for the keypad and an even cheaper one for the phone side.

It is of fairly cheap construction, but it seems adequate. The soldering is OK.

I've a feeling the micro might have some kind of standby mode, as when pressing a number key, it takes a while to respond (and may miss it if pressed quickly), but subsequent pressed are detected immediately.

I'm going to get some stuff to experiment with backlighting, as I've been wanting to play with this on various LCDs for a while anyway.

[steve30]

Well, the micro does indeed scan the keypad really slowly. If you press a key to wake it up, it goes a little faster for a while, and if the telephone is powered by the phone line (as opposed to batteries), it is fast and responsive all the time. I wonder if I can hack it to go faster all the time.

I hacked in a decent backlight as well. It only uses 200 microamps so won't have much effect on the battery.