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Multi-Purpose Car Scrolling Display, Pt.3

In Pt.3 this month, we describe how the Multi-Purpose Car Scrolling Display is connected to the car and used. It's driven using a simple command-line program.

by Mauro Grassi

When you have built and tested the PC boards and installed the driver and software as explained in last month’s article, you will then need to use the host program for calibration, to change preferences and to set up the features of the display. 

Click for larger image
Fig.1: this screen grab from Windows XP shows the properties of the command prompt shortcut used with the program cardisplay.exe. We suggest you use size 16 Lucida Console font, while the window width should be 125 and the height 58.

This is done using a PC (a laptop is preferable if the device is already installed in a car), a USB cable and the command line program for Windows: cardisplay.exe (downloadable from the SILICON CHIP website at

There are many user-changeable settings but the software is organised into multiple-choice menus which should make it clear to use. We should point out that in most cases, the default values will not need changing – you can use them as they are.

Aside from the main features described in the December 2008 issue of SILICON CHIP, there are several other features. These are battery protection (if using a car’s battery as the power source), dependent variables and limit condition messages. The latter are messages that, in the two scrolling display modes, will alert you when a variable is too low or too high. As previously mentioned, in Static Display mode, flashing and reversed modes indicate the limit conditions.

With dependent variables, you can display temperature in both degrees Celsius and Fahrenheit. More generally, you can display the same reading in different units, or show a corrected speed reading, for example.

When using the display in a car, with the car’s battery supplying power, you can enable battery protection to switch off the display when the battery level drops below a set minimum. The display will then go into standby mode with a current drain typically around 10mA.

This mode is also recommended if you want to use running totals that persist over many on/off cycles.

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