Serial interface with an older motorola phone

Using Arduino General Electronics
#1

Hi all.

I stumbled across this old blog posthttp://biobug.org/index.php/2010/02/19/lotd-clean-your-cell-phone/ a while back, about serial communications with a motorola phone. This is some awesome functionality that I really want for a project I'm working on, so I picked up one of these C168i phones on ebay right away.

I can't get it to work, and I'm running out of ideas. I am hoping maybe someone here can help?

I first made up the cable using a 3/32 headphone jack, tested for shorts with a multimeter, looks great. I hooked it up to my Uno R3 using this information for pinout Google Code Archive - Long-term storage for Google Code Project Hosting. and had no luck getting anything back from the phone, so I switched to a 5v FTDI cable and teraterm, 9600bps 8-n-1, no flow control. I had read elsewhere that the C168i uses on 3.3v TTL, so I ran the tx from the FTDI through a 5 ohm/10ohm voltage divider to get me to 3.3v, and left the FTDI rx connected straight to the FTDI, since 3.3V should still be a logic 1. Still nothing.

Anyone have any ideas? The phone has a keypad lock on it, but that first link did also. I can't find any information if motorola thought that was a security item and updated the software, but that's really the only idea I have. This isn't working at all, and it doesn't seem that complicated.

Thanks in advance.

#2

I had read elsewhere that the C168i uses on 3.3v TTL, so I ran the tx from the FTDI through a 5 ohm/10ohm voltage divider to get me to 3.3v, and left the FTDI rx connected straight to the FTDI, since 3.3V should still be a logic 1. Still nothing.

If that is truly your voltage divider, you are asking the FTDI chip to supply 333mA to drive the divider, which it cannot do. If you haven't blown up the FTDI chip, you could try a higher value divider, e.g. 510/1K.

#3

Good catch. Truth be told, the 5/10 Ohm divider was built in frustration/desperation. I started with a 5k/10k, but running out of ideas, I thought maybe the input impedance was too high. I'll give a less-extreme value a shot, too.

#4