Hy,
In my project I have arduino controlling car radio display and reading Ibus (BMW single wire 12v logic).
When desired I would need to disconnect radio mcu from display ic2 drivers and leave only arduino connected, so it takes over the display control.
At the same time I would also need ibus disconnected from the radio.
I was searching for some options online such as Dual SPDT Switch, but I am not sure what would be most suitable...
Thank you for your input.
Please show a schematic of how you have this hooked up; it makes it easier to suggest solutions.
Yeah, that might work; a simple CMOS switch. Doesn't even have to be DT; SPST would work as well, but both types are common. But to be able to see if this is a good solution, I'd want to see a schematic.
Yes SPST would be enough.
Unfurtunately I don`t have the schematic of the radio.
Basicly I traced and cutted SDA and SCL wires going from the radios main board with mcu to frontplate with lcd.
Now I need either:
Radio MCU ---->display
or
Arduino--------->display
For ibus is just matter of disconnecting wire that comes into the back of the radio.
It would be hard to write schematic as it is 3layer pcb, I can search and measure some things if anything particilar is needed.
I wasn't talking about the schematic of the radio; I assume that's not available. I only meant the schematic of the part of the circuit built by you. Is it already working, or are you still in the planning stage?
If you want to switch between the LCD being controlled by either the radio itself or the Arduino, something as simple as an SPDT or 2xSPST will work, yes. The problem, however, is if you disconnect the display from the radio and then reconnect it without toggling the radio on/off, likely the display won't work. It's likely the display is only initialized on startup by the radio. On the Arduino side you have control over this, but not on the radio side.
It will work then. I have it already working, I soldered some connectors on all wires and I can disconnect mcu and connect arduino and vice versa and it works good. Will draw something realy quick in mspaint as I am at work right now.
Sounds good, that would have been my main concern, but apparently the system is sufficiently robust to 'survive' a lost I2C connection to the display. Kudos to BMW engineers (I've never been a fan of the brand's image, but I gotta hand it to them when it comes to engineering - although my gf's Mini is a f*** b*** when it comes to its crappy VANOS system, but that's a whole different story).
As long as the Arduino and the radio operate at the same voltage (or at least within reasonable limits; let's say <300mV difference) I think you should be able to get away with some CMOS switches. Does the display stuff run on 3.3V or 5V? Make sure you're powering and controlling the display at the same voltage on both the radio and the Arduino side; it'll prevent problems in that area.
I assume you are using a resistor voltage divider to read the iBus stuff that's natively 12V, but that's a different matter than the display part.
I`m using MCP2025 transciever chip to convert ibus to ttl 5v, but I need to disconnect it from radio, not arduino, so I need to disconnect 12v side....
About BMW... yes. I would get e60, but I rather took e39 because of the problems of newer BMWs.
Radio is actualy made by Becker.
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