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Tablet as a car's multimedia system

Maciejb2 68565 34

TL;DR

  • A Nexus 7-based multimedia system was built for a 2005 Honda Civic to combine navigation, Yanosik alerts, music, and internet radio through the factory audio system.
  • A purchased enclosure and a fiberglass-and-epoxy dock hold the tablet, with charging and audio routed through an edge-mounted docking connector.
  • HC-05 Bluetooth controls sound source, charging mode, and reset, while the tablet app monitors installation voltage, charging current, and converter temperature in the background.
  • The build is designed to avoid cable clutter, minimize interference with the original radio, and allow easy tablet removal.
  • The total cost is estimated at about PLN 100, excluding the tablet and most parts taken from inventory.
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  • #31 15783312
    michalko12
    MCUs specialist  
    Posts: 3394
    Help: 462
    Rate: 321
    BigBoyPL wrote:
    In my opinion, the battery overheating may be a bigger problem, but I have not read the cell specifications yet.

    LiIon cells can be discharged to a temperature of 60 ° C, and charged up to 40 ° C (the temperature of the cells, not the environment)
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  • #32 15783332
    Maciejb2
    Level 11  
    Posts: 19
    Rate: 63
    michalko12 wrote:
    BigBoyPL wrote:
    In my opinion, the battery overheating may be a bigger problem, but I have not read the cell specifications yet.

    LiIon cells can be discharged to a temperature of 60 ° C, and charged up to 40 ° C (the temperature of the cells, not the environment)


    The option of removing the tablet was taken into account, inter alia, due to the battery, not the matrix. The console in a car left in the sun heats up to over 80 ° C. Even if the matrix was padel, I would exchange the nexus for another for a few words. If the battery caused a fire, the car would go up in smoke. Everything is under supervision while driving. However, the most important argument was the possibility of keeping the tablet function when I am not using the car.
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  • #33 15790611
    sigul
    Level 1  
    Posts: 1
    Mad Bekon wrote:


    When it comes to CAN, I mainly mean steering wheel signals.
    I have already managed to capture them, now I have to fight the Alpine DSP interface.



    Hello, could you say something more about intercepting signals from CAN :) ? I am fighting a similar project myself, nexus 7 in Vectra C where the steering wheel signals are also CAN. Regards Sigul
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  • #34 15796933
    ghrki
    Level 17  
    Posts: 158
    Help: 22
    Rate: 11
    Hello, I tried something similar in the classic Dodge Ram 1984, because the mileage counter, so I figured out that by installing a tablet-samsung galaxy 3, with GPS support and navigation with the addition of TorQue, I fixed it instead of the meter, just in front of the steering wheel. I left only the indicator lights and lights. Everything looked neat because the casing was printed on a 3D printer. and unfortunately the partner with such a non-certified meter did not pass the technical inspection. It's a pity because everything worked on android and I generally used ready-made solutions programmatically. because the tablet had OTA options, I connected a webcam to it and recorded it with the Black Box program.
    when I find photos I will share it.
    At the beginning she was sneezing because handling the touch by the steering wheels could have ended in an accident, but I solved it by trackball - it's such a bigger mouse.
    ps it really was so close that he had a checkup - only the diagnostician was too inquisitive
  • #35 16496195
    hetm4n
    Level 20  
    Posts: 812
    Help: 5
    Rate: 525
    How to solve the problem of battery overheating? I have a tablet in Almeria n16, in the upper part of the cockpit, when it's outside at 25 degrees and it's sunny, the tablet goes crazy, overheated battery, and punishes to disconnect the charging, after a long time it turns itself off and resets non-stop until it is cold. Is it possible to make some thermal insulation or is it better to remove the batteries and make a battery accumulator from a permanently connected voltage? Umnie, I have it done with the tablet after disconnecting the ignition switch disconnects the charging, which results in the screen blank.
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Topic summary

✨ The discussion revolves around the integration of a Nexus 7 tablet as a multimedia system in a 2005 Honda Civic. The user aimed to create a multifunctional interface that supports navigation, internet radio, and music playback through the factory audio system, while minimizing cable clutter and maintaining the original radio's functionality. Various responses highlight the project's design, including the use of a custom docking station made from fiberglass and epoxy resin, and the potential for car diagnostics using OBD-II protocols. Participants express interest in the software used for internet radio, the connection methods to the car's audio system, and the challenges of temperature management for the tablet. Suggestions for enhancements, such as adding a reversing camera and improving diagnostics capabilities, are also discussed.
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FAQ

TL;DR: For ≈PLN 100 (~US $25) in extra parts you can turn a Nexus 7 into a detachable head-unit offering audio, GPS, radio-streaming and OBD reads; “the radio did not have an AUX—so I grafted one” [Elektroda, Maciejb2, post #15767556]

Why it matters: You add modern functions without losing the stock look or paying for an aftermarket deck.

Quick Facts

• Build parts cost: approx. PLN 100, tablet excluded [Elektroda, Maciejb2, post #15765150] • Nexus 7 pogo/dock pins carry 5 V / 2 A plus stereo audio and USB [XDA Dock Thread] • Li-ion safe charging temperature ≤ 40 °C; discharge up to 60 °C [TI, 2019] • Bluetooth ELM327 OBD dongle price: US $4 shipped [Elektroda, Anonymous, post #15766173] • CLAA070WP03 LCD rated −20 °C to 70 °C operating range [Chunghwa Datasheet]

How do I feed tablet audio into a factory radio that lacks an AUX input?

Tap the radio tuner’s left, right and ground lines, cut the original wires, and reroute them through a two-pole switch. This places the tablet signal where the tuner used to be, keeping volume control intact [Elektroda, Maciejb2, post #15767556]

Is there a quick 3-step method for adding that line input?

  1. Open the radio and locate the tuner board leads marked L, R and GND. 2. Desolder L and R, add shielded wires from the tablet dock. 3. Wire a DPDT switch so up = radio, down = tablet, then reassemble [Elektroda, Maciejb2, post #15767556]

Which app shows four resizable windows and streams internet radio?

The author built it in MIT App Inventor 2; it parses stream URLs and displays four touch zones [Elektroda, Maciejb2, post #15767556] The shared .aia file is in post #15777650.

What Android software should I use for OBD-II diagnostics?

Torque Pro supports ELM327 Bluetooth adapters, decodes live PIDs and resets DTCs; it exceeds 10 million downloads on Google Play [Play Store stats]. Post #15768018 links the free version [Elektroda, Greg43, post #15768018]

Will the tablet screen or battery survive summer heat in a parked car?

The Nexus 7 LCD is rated up to 70 °C [Chunghwa Datasheet], but its Li-ion pack must not charge above 40 °C [TI, 2019]. Designers therefore make the unit removable; cabin plastic can reach 80 °C under sun [Elektroda, Maciejb2, post #15783332]

How do I stop alternator whine and DC-DC converter noise?

Run audio ground and power ground together to the same point on the radio harness, keep loops short, and add LC input filters to the 5 V converter. Poor grounding caused two months of audible whine in the build [Elektroda, Maciejb2, post #15768581]

What microcontroller logic controls charging and source switching?

An ATmega8A measures converter temperature, charge current and vehicle voltage on its ADC pins, then toggles three relays: 1) audio source, 2) charger on/off, 3) 5 V vs 3.3 V dock mode. Commands arrive via an HC-05 Bluetooth UART [Elektroda, Maciejb2, post #15768581]

Can steering-wheel buttons still work after the tablet swap?

Yes. Capture CAN-bus key frames with a transceiver (e.g., MCP2515) and map them to keyboard HID codes or UART packets sent to the tablet. A contributor already logged Golf wheel frames and now pipes them to an Alpine DSP [Elektroda, Mad Bekon, post #15772580]

How much total does the project cost including a used Nexus 7?

Used 2nd-gen Nexus 7 tablets list for PLN 250–350 (US $60–85) on Polish auction sites [Allegro listings]. Add the PLN 100 interface cost and you stay below PLN 450, roughly 9 % of a branded Android head-unit priced at PLN 4 800 [Retail survey].

What happens if I replace my speedometer cluster with a tablet?

One owner’s 1984 Dodge failed inspection because the tablet meter was "non-certified" [Elektroda, ghrki, post #15796933] Keep factory gauges or run the tablet as a secondary display to avoid legal rejection.

How can I integrate a reverse camera without lag yet keep the tablet removable?

Use a USB UVC camera on a powered hub behind the dash; Android recognizes it instantly. Wireless cameras add ≥250 ms delay and compression artifacts [Elektroda, Mad Bekon, post #15772580]

What’s the fix for battery overheating warnings during sunny parking?

Remove the tablet when parked, or bypass the internal pack and power the device from a regulated 5 V rail so no cell charges while hot. Almería owner sees shut-downs at 25 °C ambient with sun exposure [Elektroda, hetm4n, post #16496195] External packs allow fan-cooled or remote-mounted cells.
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