RS232 to TTL at 3.3v

[gareth41]

I need to connect to the 4pin TTL header on a router to recover a bad flash using tftp. Question is: would I be able to somehow adapt a Jaycar programmer to do this? I see its got all the required components for a RS232 to TTL

[nzdong]

This is what I always do - convert a USB-to-serial RS-232 cable to a USB-to-serial TTL cable.

(1) Get a USB-to-serial RS-232 converter cable from Jaycar (make sure that the circuit part is not over-molded and is accessible). A common one would be using PL2303 chipset (or compatible).
(2) Open the cover for the PCB. You should see two chipsets on the PCB. One is PL2303 which converts USB to serial TTL level. The other one is the RS-232 converter chipset.
(3) The connection between them are: DB9 <-> RS232 conveter <-> PL2302. We know that pin 2 of DB9 is RX and pin 3 of DB9 is TX. Remove RS232 converter chip and short pin 2 and pin 3 directly to PL2302 (or the input/output pins on the RS232 chip from PL2302).

If you are not good at doing this, then you can probably find a USB-to-serial TTL level converter cable from ebay.

[Adobe]

I have a blackcat USb device for this is you want it brand new works with 5volt and 3.3 volt TTL $30.00 P&H

Adobe

[gareth41]

thanks, I sorted it out in the end. I found a spare MAX3232 I had lying around which I bought a few years back, for Jaycar 3.3v mod which I never ended up doing. Only had to solder it up with a few 100n ceramic caps plus wiring to the header on router pcb, I got a terminal session established and tftp'd the firmware back following a wiki at openwrt.org.