[DW] sums up

[…] a description of the methodology of reverse engineering a simple hardware device. […] (to make a custom) USB-to-TTL serial cable to upload our own custom code

The CA-42 “Nokia” cellphone data cable was shown to be a good start for an Arduino cable conversion. Recognizable IC’s with part numbers screened on. Piece of cake! Search eBay for “CA-42” and you’ll find tons. Beware the old cheap-sale-price-expensive-shipping phenomenon.

The pinout for Nokia phones is well-covered on the net, and with a continuity tester I traced back from the Nokia connector to the PCB.

So I found that:

phone connector pin 8 (GND) —> orange wire —> PCB pad 6

phone connector pin 7 (TX) —> blue wire —> PCB pad 12

phone connector pin 6 (RX) —> red wire —> PCB pad 9

Read the step by step guide from [KwartzLab]