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Finally going to do it!

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  • Finally going to do it!

    I'm finally building the carpc I've wanted to build for 5 years!

    It's going to go into a 2006 Crown Vic Police Interceptor. I intend to use ride runner, and I'm building as much as I can from "scratch".

    I'll be using an Acer Aspire One as the PC, and I've got an old slide-out single din VGA touchscreen I'll be using for the monitor (If I didn't already have this from long ago, I'd use a double din permanent touchscreen as it would fit better in this car). The netbook would also be something simpler as well if I didn't already have one with a broken connector for the power supply (I'll pigtail it because I'm cheap).

    I intend to release all the schematics for my build once I'm done, as I know that I've had a hard time finding simple designs for these things (Especially the power button dealy--I didn't like the ones I've seen here, and one of the items has gone commercial so no more schematics). Here's what I'll be building:

    - 5v USB power supply, switching, 3A (DONE) (Using LM2576)
    - 19v (adjustable) switching power supply for the netbook, 2A (DONE) (Using LM2587)
    - Automatic power-on power button "pusher" (a relay that is activated for a moment after a short delay once dome light power is on) (DONE) (Using 2 x 555 Timer)
    - 4 x 50W amplifier using TDA7851L or TDA7850 (I have both) (To build)
    - TDA7419 based audio control (will provide 3-band equalizer adjustments, balance, and fade, along with 3 selectable inputs) (To build)
    - Si4734 based AM/FM radio (To build)
    - Controlling the above two items with an Arduino via I2C using BSS138 FETs for level conversion

    I have all the parts, I just need the time now! Hopefully I'll get it done by PAX East... what do you think?

    Let me know if you have any other ideas!

  • #2

    - Netbook runs on the custom power supply, and automatically powers-on with the relay
    - VGA single-DIN Touchscreen works well with the netbook
    - 5v USB PSU works and data passthrough is fine
    - Arduino is now controlling the TDA7419
    - Installed a backup camera in my bumper!

    To resolve:
    - TDA7851L is not providing any output. I'll have to diagnose why shortly.
    - Have soldered together, but not attempted control of Si4734


    • #3
      Alright, TDA7851L works. I didn't have the ST-BY and MUTE lines connected properly. Not loud enough, though, because apparently the TDA7419 has a rather quiet output. I threw in a TL084 to fix that, nice and loud now.

      Unfortunately, the TDA7419 seems to be generating some noise internally, a static sound that seems to only come out the tweeter. I'm guessing it has to do with the AC Coupling caps that are present in the test design in the datasheet. I'll remove them and see if things improve.

      I might just get this done for PAX after all!


      • #4
        Alright! All the noise issues have been solved. The main source of them was using the chip in AC coupling mode--it offers a DC coupling mode which was hard to find. Also, the arduino was injecting noise into the ground on the circuit. Isolating it with a 100 Ohm resistor solved the issue. The volume issues have also been solved--DC coupling mode allows 4 V pp output from the audio IC! Sound absolutely excellent, too.

        All that is left is:

        - Writing the full code for the arduino, it needs to work with the radio IC and an analog potentiometer for volume
        - Controlling the radio IC
        - Writing a PC interface for all this

        If I don't run into any other major roadblocks, this won't take long at all!


        • #5
          - Code for analog potentiometer -> I2C commands working perfectly
          - Interfacing via and serial port -> I2C commands working perfectly

          To finish:

          - Controlling radio IC
          - Creating a nice looking interface
          - Installation into the car.

          I think I'll leave the radio IC on the backburner for the trip and use my PC Ear for now. I'm short on time. I figure in a month or so I'll have some decent documentation to give you all. This is definitely the right way to do the job!