electronics

28 feb 2020

roadster electronics

these pages lag behind reality and are erratically updated.

the hardware here was designed for the roadster project but is quite generalized. it's aimed at closed loop motor/motion control with analog feedback and various digital and analog controls and sensors. automotive environment meaning norminal 12 volts negative ground, high current (1 to 25 amp) nasty inductive loads (so things like LEDs are trivial). sensors and inputs are low-impedance. power control, management, and filtration designed in. PWM control of everything heavy. internal thermal management. flexible/configurable analog/logic input networks.

there are two boards, POWER and ANALOG. these are Arduino Mega 2560 format stackable boards, use either or both (roadster computers all use both). here is the documentation for the boards, schematics and gerber files. if the Eagle files are interesting let me know i'll put them up. the BOMs are not very good however.

both ANALOG and POWER boards work with Arduino Mega 2560 and Arduino DUE, and should work as-is with the soon-to-exist AdaFruit "Metro Grand Central" board with a fully-broken-out 120 MHz SAMD51 processor. woo woo!

here is the code that drives this hardware. the Cooling computer has it's own page.

the panel computer looks more like what most people think a computer is. it contains the same ANALOG and POWER boards but has a large LCD and some glue logic for it and the required manual controls.

ANALOG

the analog board has analog and logical inputs, and four modest power outputs.

• six analog inputs zero-to-positive voltage, low-impedance (under 100K Z), or 5-volt-fed resistive sensor inputs (eg. NTC resistors or pots). opamp isolated, lockup prevention, etc
• accurate ADC, 1% components, LM4040 ADC reference and resistive-sensor pullup voltmeter.
• six logical (binary) inputs, with input networks for pull up, pull down, diode-isolated pull down, etc. library code for user-event control (short, long press switches, rotary encoders, etc)
• two edge-trigger, interrupt-generating inputs, 5V, 12V tolerant.
• four 1-ampere PWM capable automotive high-side driver outputs, with configurable power source (internal 5V, VIN, or external). one output ready for inductive load (eg. POWER board MOSFET cooling fan).
• realime calendar/clock chip and support (DS1388).
• two bidirectional RS-232 serial interfaces (DS3232).
• jumper configurable for 5V or 3.3V logic (Mega 2560 or DUE).
• .1" SIP break-outs for SPI/IIC.

POWER

the power board contains eight high-current automotive high-side drivers, board/system power management, output load current sense, load power source voltmeter. the VN5E010 chips provide short-circuit protection, load dump and reverse battery protection, and have internal thermal management and feedback, all supported by the board and code.

• eight VN5E010 10 milliohm high-side drivers with current feedback, short circuit protection, etc.
• thermal design accommodates an unknown-at-this-time total board power throughput that has been tested so far to 25 amps (limit of my power supply) of mixed resistive/inductive loads at half power PWM (worst case).
• fast load commutator diodes and separate diode load ground.
• discrete MOSFET temperature sensor and active MOSFET temperature control.
• load current feedback measurement and code support.
• load power supply voltmeter.
• system/board stack power management; external "power on" signal and internal power-on override.
• split or combine three power-input sources (load, local, "on" signal).

ASSEMBLY

the boards stack onto each other, and an Arduino Mega 2560, and fit into a semi-open plastic box which is mounted to the inner firewall. the boards are plastic spray coated to protect against condensation.