SIO2USB - a debugging cable for the sony PSP

when i started creating homebrew software for the sony PSP it was a real pain loading the software in, starting it, testing and so on. i had to go to the vsh, scroll left, activate the USB, load my piece of software in, deactivate USB, scroll right, open my program, waiting for the gameboot animation and then testing... as i said: a real pain.

then i found out about TyRaNiDs tool PSPLINK - this saved me lots of time during development. it creates a shell over the serial or wifi interface where you can start, stop and debug your software remotely. no need to do all that boring switching, just set up some scripts and everything is running almost automatically. additionally, the stdout is redirected to your console, so you can easily output debug messages without disturbing your PSP screen layout.

first i was only using the wifi interface, but as i read in the forum, other people liked the SIO interface as well. the SIO is originally an interface to the remote control for the PSP, but as it is run over a RS232 protocol with 2.5 V, it is possible to connect to a pc via a basic electronic circuit. the only reason why i did not use it was the lack of a serial port on my laptop. well, i additionally didn't want to buy a USB2Serial converter, so i decided to create a direct SIO2USB circuit. i created a schematic and pcb layout and nailed the components on it. the device does its job well, and here i want to share the information for anybody to use it for his own debugging environment.

here are some technical details: klick on the picture on the left to get a full size view of the schematic. in the middle you see the USB to serial converter chip (FT232), around are some necessary components (all SMD). The chip is configured to be a bus powered device operated at 3.3 V, so we are close to the voltage of 2.5 V used inside the PSP. for safety, a resistive divider reduces the 3.3 V output (TXD) to a 2.5 V level. on the other side (RXD) there's no problem with signals lower than 3.3 V. in fact, the input will accept signals as low as 1.5 V if powered at 3.3 V.

as connector i used the original remote control which comes shipped with the PSP. i cut the cable in the middle and the SIO2USB is constructed in a way so you can solder both ends of this cable to the PCB. this way you keep the functionality of the remote control. a jumper is used to switch the TXD channel between USB and remote control. as a nifty extra a small led shows when there is traffic along the RXD or TXD line, so there's always some nice blinking going on. btw: most of the information needed to create this cable i found here and here.

if you want to create your own pcb from my schematic, you can use the images on the right side. click on them for a higher resolution image. if you print them out at 400 dpi, they will be to scale. a few comments: the first image is for the top layer, the second for the bottom layer. on the right side of the top layer you see the three holes for the jumper, left next to them three vias (you have to solder to the other side on those three positions). the "hole" under the USB chip is just an index marking so there's no mistake during assembly. if anybody is really interested, i bring the rest of the info online (bill of materials, placement and names of the components etc.).

for now this should be enough as a short sketch of the project. if anybody wants me to make such a circuit for him, or has some suggestions, drop me a message (thoraltthoralt.de).

a last word: if you build yourself such a device, be warned, that it is possible, yet unlikely, to fry your PSP, your computer or both. i take no responsibility for any damage to you or your PSP/PC.



downloads
here you can download some files associated with this project:

schematic (cadsoft eagle schematic, 226 k)
circuit board (cadsoft eagle board, 21 k)