what chip is buried under my display

Hi Everyone,

I had an old CO detector that went bad so figured I'd scavenge it. There's a nice little 7 segment 3 digit LCD display on it with a 5 wire ribbon cable. The display is mounted to a bit of PCB and of course underneath the display is the driver chip so I can't see what chip it is. Only 4 of the 5 ribbon cable wires actually are connected so I figured it's I2C. On the main board of the detector was an I2C EEPROM so I was able to figure out the wiring to the display (SDA/SCL/VCC/GND) easily enough since it shared the bus. I ran some i2c scanner code on the arduino and it easily found the driver chip, it's address is 0x3E.

I tried a couple libraries and things to get it going and nothing I've tried lights up any segments.

Now for the big question. Does anyone have any idea how I might be able to figure out what that hidden driver IC is w/o desoldering the display from the PCB. It's such a nice little assembly I'd really like to keep it as-is. The display itself is common cathode, 24pin, and if I ground pin 24 it illuminates all the segments at once. I know, doesn't really tell you anything about the driver chip probably.

Thanks for any suggestions.

Googling for a few minutes with your information and the search "i2c 0x3e led", results in sx1507 and 1508. This one is exactly meant for driving LEDs, and it's base address is 0x3E and can also be set to 0x3F, 0x70 and 0x71 by jumpering pins to LOW or HIGH.

Seems to be a good guess, found a datasheet here (click !). So have a peek and see if that helps you to get things going.

Thanks for the tip. I had also found yet another one using 0x3E that I tried and it wasn't it. The one you had found also wasn't it. It turned out to be some variant of the NXP PCF8566 that I came across, yet a third using 0x3E. I'm pretty familiar with those PCF chips and their command structure and the commands turned out to work, although the segment map isn't what's in that datasheet, so I had to light up each segment one by one by sending in 2,4,8,16, etc and making my own map. Now I can totally use it. Have it counting up to 999 and restarting now :)....thanks for the assist!