Thread: Renault "Tuner List" Head Unit/CD changer hacking - Controls

Originally Posted by Vicne

- the fact that CristianC could connect the pin directly to a PC. Indeed, at 1V/12V, the use of the MAX 232 is questionable for most recent PCs that have their threshold above 1V. I would like to hear the opinion of people used to serial communications (Ale again ?) about the removal of the MAX3232 altogether... Only for data coming from the PC probably would it be wiser to change levels I think (at least to avoid sending negative voltage to the CDC)

(*) in fact, the divider could probably be removed too.

I think that if the max3232 without the divider, receive data correctly, you can connect the HU to pc rs232 directly, becouse PC receiver probably is max232 or similar (I have found another EIA-232-D/V.28 driver/receiver MC145406 that has the same threshold: "The actual turn-on input switchpoint is typically biased at 1.8V above ground, and includes 800mV of hysteresis
for noise rejection. The nominal input impedance is 5k").
for the connection of Txd PC-HU i'll think for a simple schematic with a transistor or a cmos buffer...
good night!!

Originally Posted by Ale

for the connection of Txd PC-HU i'll think for a simple schematic with a transistor or a cmos buffer...
good night!!

I'd suggest to consider an extra line to connect the remote output of the hu to cts, so that the pc can check that the hu is on or off and start communication accordingly. (a pull down resistor should be enough if you don't want to get fancy).

As far as I know CTS/RTS and DCD/DTR are hardware handshaking signals but controlled by means of software. If you configure the serial port not to use hardware handshaking the signals are ignored and can be used for something else. You could try it, disconnect the bridges that you made on the RS232 connector and link it to your spy-circuit. Use Hyperterminal, switch of handshaking (hard and software) and see if data comes through, it should work. I say Hyperterminal because I have no idea how your MTTTY code is handling handshaking, in Hyperterminal you can switch it off, or any other terminal software that has this option of course.

Originally Posted by Vicne

Can we have a reliable communication without the CTS input and use it for another purpose ?

Of course you can, I do it all the time.
In windows you set the correct flags in DCB in a call to SetCommState, with synaser you call the config method passing false as hardflow (and softflow too, but that's another matter).

We could also send this remote to the ACC of the PC power supply (M1 ATX in my case) so that PC hibernates when HU stops and resumes when HU starts :-)
Note : if RTS/CTS aren't mandatory for handshaking, can I use the RTS output for another purpose too ?

I think you can, though I never did that (in a project I'm using a serial port as a single digital input, but I don't use it for communication).
Windows api for writing the control lines is EscapeCommFunction and GetCommModemStatus for reading, synaser has the properties RTS and DTR (write only) and CTS,DSR (read only).

Originally Posted by Vicne

Cool. I never tried that. I'm asking because I'd like to switch my relays from CDC to PC only when the PC is booted and ready to fake the changer ;-)

You could also use the parallel port: I'm using a circuit like the second one here (the one under "safer new design"), the only problem is that the data pins are active for a very short while when the pc is switched on/reset. It's not a problem in my application but it's going to be in yours. Maybe the serial port (or the parallel port in your motherboard) doesn't exhibit the same problem. You can check it with an oscilloscope or simply building the circuit and see if the relays energizes when turning on the pc. If it does you can add a delay circuit.