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?
- 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, #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, #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.
? I am fighting a similar project myself, nexus 7 in Vectra C where the steering wheel signals are also CAN. Regards Sigul
