From the outside, cars manufactured today look much like the ones rolled out 10 years ago. The shape and interior design has not changed much since the turn of the century because there have not been many improvements in the aerodynamics and basic comfort features.
Electronics, however, have increased exponentially. Connected cars, equipped with new car-to-car (C2C) and car-to-infrastructure (C2X) technologies, are expected to pack in around $6,000 of electronics by 2022.
While many of the cars in the middle to high end of the market are already equipped with digital interfaces (i.e., touchscreen panels or tablet-like displays), contact monitors – the ones where you push a physical button or turn a knob – are still preferred for many user-interface features.
Drivers need simple buttons and knobs to turn lights on and off, start and control the windshield wipers, signal turns and lane changes, and change the basic information displayed on the dashboard. Additional features, such as adjusting the volume of the audio system or changing radio channels, are better performed by drivers using buttons on the steering wheel.
BCMs – issues with space, reliability, power consumption and cost
While it is possible to reduce most of the electronic functionality of a car to a few chipsets, especially new system-on-a-chip (SoC) subsystems, the need for basic connectors for the driver-controlled functions has not gone away. Body control modules (BCM) are, and will be for a while, the basic system to connect all the knobs and switches being used.
A BCM is the electronic control unit responsible for monitoring and controlling various electronic accessories in a vehicle’s body, such as power windows, power mirrors, air conditioning, and the vehicle’s central locking system.
In fact, the number of buttons and switches on the dashboard and steering wheel have doubled in the past 20 years. The need to control the increased amount of technology, including new comfort features, means that BCMs become larger, compromising space within the vehicle itself.
There are two types of switches in a vehicle. If a switch only has two states, open and closed, it can be categorized as a digital switch. Examples of digital switches include the seat belt switch, front and rear fog push button, the trunk switch and the door locking switch. Other switches have different values, depending on the position of the switch; they are referred to as resistor-coded or analog switches. Examples include headlight knobs and the windshield-wiper switch.
As the number of connections increases, power consumption rises, which is critical to body interface design. The higher power usage also means that larger BCMs create more heat and are prone to failure.
More importantly, though, a larger BCM is costly. Not only will the bill of materials (BoM) grow with additional switches, knobs and cables, but the larger BCM will take up more space and probably will have to be divided into several units to accommodate the various connections and components.
MSDI technology can overcome these problems
Basic BCM design has not changed much over the years. BCMs have simply become larger to accommodate the new switches, adding new connectors, diodes, resistors, and other components as necessary.
The key to solving the above-mentioned problems and simplifying the design of new BCMs is to use multi-switch detection interface (MSDI) technology. An MSDI allows you to connect several switches and power levers to the same connectors using a grid detection system to determine which switch has been used. Based on the simultaneous activation of two or more connectors, the MSDI device can initiate the right action on the control board, sending the signal to the appropriate subsystem in the car.
A single MSDI can substitute a large number of switches, reducing the space needed for the BCM. It also reduces the number of connections and components and can save up to 40% of control switchboard space.
What’s more, a significant advantage of this design is scalability. The large number of switches that a single MSDI-based module can handle is not necessarily needed in many vehicle models, but using the same board across different configurations, and different lines, simplifies the design and supply chain, with a corresponding reduction in cost and potential problems. If additional switches are later needed to incorporate new features, the system is already in place.
As many car functions need to implement different values on the same switch (i.e., different windshield-wiper speeds), detection is normally done by adding resistors for each value to the control interface. An MSDI includes power-level detection, which can provide multiple values with fewer resistors.
For example, the TIDA-01237 module by Texas Instruments, incorporates the TIC12400 MSDI chipset and features a 3.3-V low-dropout regulator. The system, using only 12 pins, can handle signals from 36 different switches, saving 24 I/O pins, thus significantly reducing the space needed for the device. Additionally, this module can handle analog input, Hall sensor inputs, and multi-position switch inputs using a 6 x 6 matrix configuration.
The centralized architecture of MSDI technology, without having to use several BCM boards in the vehicle, simplifies troubleshooting and maintenance as there is only one component to diagnose and potentially replace. Furthermore, reducing the number of components and their size and using low-polling mode for most functions can yield a system-wide power savings by as much as 98% in some applications. The reduced BoM, coupled with the smaller space needed for the BCM, also means that both cost and power consumption are further reduced.
Choosing the right partner
MSDI solutions may still be relatively new to the rest of the industry, but Texas Instruments has long been involved with the technology. And with over 30 years of experience in the automotive industry and a wide selection of reference designs and training materials, TI can help you design differentiated body electronics for any type of vehicle.
To learn more about MSDI solutions, contact Texas Instruments.