Hi, I have an Arduino mega to which I have attatched a MAX485 chip. The MAX485 is powered by the 5v out on the mega. I'm using RX1 & TX1 to talk to the MAX485. The output side of the MAX485 is connected to a Ford 6000CD car radio. The escence of the project is to emulate a CD multi changer connected to the radio. I followed a tutorial herehttp://www.instructables.com/id/Ford-CD-Emulator-Arduino-Mega/#step1.
The problem is this, if I power the mega using USB from my laptop or an external USB power source and the radio from a desktop 12v supply, all is well and the radio recognises the mega as being a CD changer, ie the comms between the mega-MAX485 and radio work as expected.
However, I would like to power both the radio and the mega from the same 12v supply so I connected a 12vDC-9vDC power board to the 12v supply then to the mega and also the radio to the 12v supply. With this setup the mega no longer talks to the radio.
I don't understand why using the same power source to power both units would cause it to fail. I have done some reading and suspect there is feedback, interference or something that is causing it to fail, I suspect that some kind of decoupling capacitor or filter is required but I don't have any understanding of this.
Please could someone help me out with this, if anyone knows why this issue occurs then please could you enlighten me as I can't for the life of me work it out.
Thanks in advance, regards, Rick.