Controlling External Alphanumeric Displays

There can be situations where it’s not sufficient to monitor your system via an attached screen or remotely via the network. It can make sense to have monitoring capabilities directly at the computer’s enclosure, especially if the system is not equipped with a screen. Servers running in a “headless” configuration, i.e. without a monitor attached, are a good example.

For this type of configuration, Hardware Monitor can send readings to an external alphanumeric liquid crystal display (LCD) which can be connected to the computer via USB interface. An example is shown in the following photo:

LCD output example
LCD output example

In addition to acquired readings from sensors and probes, Hardware Monitor allows you to specify additional data for output as well, for example the current time, or the IP address of a certain network interface. The example above shows date and time, a bar graph for the load of 4 processor cores, a power value, a selected temperature, the S.M.A.R.T. state of the hard drive and its temperature, and the revs value of the main fan. The contents of the display is updated at the same rate as all other output channels of Hardware Monitor.

Hardware Monitor supports the following hardware equipment only:

When attaching these devices, no additional device drivers need to be installed.

We cannot answer any questions about these hardware devices or their distribution. We do not promote or sell these products. Regarding any questions about building or configuring your own LCD output unit, please see the following web sites for documentation and contact information:

Information about products not manufactured by us or about third-party websites is provided for reference purposes only, and does not constitute our recommendation or endorsement. Please contact the respective vendors for additional information. We provide this only as a convenience to our users. We have not tested the information found on these sites and make no representations regarding its accuracy or reliability. There are risks inherent in the use of any information or products found on the Internet, and we assume no responsibility in this regard. Please understand that a third-party site is independent from us and that we have no control over the content on that website.

Configuring display units

Configuration of an external LCD unit is very easy and can be done by simple drag-and-drop operations.

  1. Connect one or more external LCD units to the USB interface of your computer.
  2. Launch Hardware Monitor, open the Preferences window and go to the section LCD Module.
  3. All detected USB units will be displayed in the small table at the top of the window. To select which type of LC display is connected to each USB unit, click on a line in the table, then use the pop-up menu Configure selected USB device for display type to choose how many lines and columns are available on the display. The button Run Test… can be used to send a test pattern to the selected LCD.

The LC Display will light up as soon as you switch the type menu from No display to one of the possible display types. The following test patterns are available:

Note: Katakana characters are only available with the original version of the Hitachi HD44780 LCD controller. Modern versions of the chip may support different character sets when sold in different regions of the world. You might see accented European characters for example, or Cyrillic characters replacing Katakana in specific implementations of LCD units.

If the selected LCD module is capable of controlling additional settings via software, the button LCD Settings will become active. After pressing it, a dialog sheet will open and you can set operating parameters as backlight brightness or display contrast.

You can additionally activate a “backlight saver” for each of your LCD modules which makes sure that the display will be switched off after your computer has not been in use for a specified time. Just select the desired time (or the value never) with the slider at Start backlight saver. It’s a good idea to select the same time interval you have set for your screen saver in System Preferences but this is not necessarily required.

The IO-Warrior USB controller does not need any drivers to be accessible by macOS. To make this technically possible, it acts like a Human Interface Device (HID), similar to a mouse or keyboard. For this reason, macOS will interpret certain signals of the IO-Warrior device as “user interaction”, causing your system to no longer enter any sleep modes when the module is active. If you want to use automatic sleep mode for your screen or your computer, you’ll have to enable the backlight saver for the IO-Warrior module. In this case, communication to the LCD module will stop after the selected time interval. At that moment, macOS will no longer misinterpret the module as active user, and the standard sleep interval timers will start as expected. Note that the total sleep timeout interval will be the sum of the LCD backlight saver time and the sleep time you have configured in the Energy Saver pane of System Preferences.

Hardware Monitor Preferences: LCD Module
Hardware Monitor Preferences: LCD Module

After the display type has been configured, you can use the lower part of the window to select which output elements should be sent to the display. The left table shows you all output elements which are available on the local computer. The right table shows you the active elements which are currently being sent to the display. At the beginning, the right-hand table is empty. You can use the mouse, dragging elements from the left to the right table to configure the desired output step by step.

The selected output elements will appear immediately on the display, showing the current values. The display follows the update time interval you have set in the General pane of the preferences window. The output will appear additionally in the simulated Preview area in the lower left corner of the window.

The output elements are sent to the display in top to bottom order. You can rearrange the elements by dragging them in the right-hand table into any order you like. The following elements are available for output on the external display:

If you have selected a sensor or probe value for output, you can enter additional parameters at Options for selected element:

There are no restrictions in the output elements you select. You can use several different text elements for example, or display the same sensor value twice, at two different locations on the LCD. Hardware Monitor won’t warn you if you are creating more output than fits on the display.

Using LCD units on an unattended computer

It is necessary to have Hardware Monitor running in order to send values to the external LCD unit. However, if you log out, macOS will automatically quit your running applications. This means Hardware Monitor will be shut down and the display will be switched off. This is not helpful if you want to monitor a server, which is usually running in unattended mode with no user being logged in at the main screen.

You can solve this problem as follows:

  1. Download a copy of Hardware Monitor Remote. If running on the same computer for the same user, only one registration key is necessary to use both applications.
  2. Attach the LCD unit and use Hardware Monitor to configure the display. When the output works as desired, quit Hardware Monitor.
  3. Launch Hardware Monitor Remote on the same computer and user account, and use its import feature to import the current LCD configuration (together with the current probe configuration if necessary) from Hardware Monitor. See the reference manual of Hardware Monitor Remote for details.
  4. Start the background service of Hardware Monitor Remote. The background application will control the LCD unit, and the display will remain active even if you log out.

You can also configure Hardware Monitor Remote to start the background service automatically during startup of macOS. In this case, the display will automatically be switched on when the operating system is started. It is not necessary that a user logs in.

Connecting and disconnecting running display units

Hardware Monitor and Hardware Monitor Remote allow that you connect and disconnect external LCD units while they are in use. The applications can identify each unit and will automatically stop or restart sending data to each unit, if the displays are disconnected or reconnected to the computer, respectively.

Attention Warning: Despite this feature, some versions of macOS might not support this hot-swapping of devices! In the worst case, macOS might crash with a kernel panic when you disconnect an LCD device in the middle of a running data transfer. This is a problem in the USB drivers of macOS which cannot be prevented by Hardware Monitor. For this reason, it is recommended to disconnect LCD units only after you have quit the application which is controlling it.