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USB Clock With LCD Readout Pt.2: By MAURO GRASSI Last month, we detailed the circuit of the USB Clock and showed you how to build it. This month, we detail the software installation and describe how it is used. We also describe how to synchronise your PC to an internet time server and how to synchronise the USB Clock to the PC each time the PC boots up. H AVING BUILT the hardware, the next step is to install the necessary driver. The following outlines the steps for Windows XP but other Windows versions, including Windows Vista, should work similarly. The first step is to download the Microchip installer (MCHPFSUSB_ Setup_v1.3.exe) from the SILICON CHIP website and run it (it’s in the November 2008 downloads section). Note that you must use version 1.3, as older or newer versions may not be compatible. When you run the installer, this will copy the driver to the C:\MCHPFUSB\ PC\MCHPUSB Driver\Release folder. Subsequently, when you first connect the USB Clock to your computer, Windows will recognise the device as a “Microchip Custom USB device”. siliconchip.com.au The “Found New Hardware” dialog will then appear (see Fig.7) and you should select the “No, not this time” option and click “Next”. At the following dialog, select “Install from a list or specific location” and click “Next” again to bring up the dialog shown in Fig.8. Select “Search for the best driver in these locations” and enable the “Include this location in the search” box. Now click the “Browse” button. In the “Locate File” dialog that appears, navigate to where the MCHPUSB files were installed (normally it will be C:\ MCHPFUSB\PC\MCHPUSB Driver\ Release folder) and select “mchpusb. inf”. Click “Next” and Windows will then install the driver. If the driver is installed correctly, you should be able to see the “Microchip Custom USB Device” entry in Device Manager (provided the USB Clock is connected), as shown in Fig.9 (Control Panel -> System -> Hardware Tab -> Device Manager tab). Installing/using usbclock.exe Once the driver has been installed, you can control the USB clock using the usbclock.exe program. The first step is to download this program from the SILICON CHIP website (November 2008 downloads section), unzip it and copy it to a suitable folder (eg, create a folder called “usbclock”). Usbclock.exe is a simple program that’s run from the Command Prompt dialog (formerly known as a DOS box). It’s simply a matter of navigating to the November 2008  35 Fig.7: this is the dialog that appears the first time the USB clock is connected to the PC. Select the option shown and click the “Next” button. Fig.8: selecting “Install from a list or specific location” brings up this dialog. Select the options shown and click the “Next” button. Windows then installs the driver. Fig.9: this entry will appear in Device Manager if the driver is installed correctly. folder where the program resides, then typing usbclock to synchronise the USB Clock with the clock on the PC. For other functions, simply enter usbclock x at the command prompt, substituting the appropriate switch for the “x”. Table 4 shows the various command line switches and their functions. Among other things, you can view the current operating settings (-i), change the PWM duty cycle (and thus the brightness) of the backlight (-p:X), set the backlight timeout period (-t:X), set the auto-backlighting on or off (-a:X) and change the display format from 36  Silicon Chip Fig.10: the USB clock is synchronised with your PC’s time by running the usbclock.exe program from a command window. This screen grab shows the output after running usbclock -i to view all the clock’s operating settings. the default 24-hour time to 12-hour format (-y:X). Fig.10 shows a typical example of the screen that appears when the usbclock program is run. Driving the USB Clock There’s only one control on the front panel of the USB Clock and that’s pushbutton switch S1. You simply press S1 to turn on the backlight. This will be turned on for the duration of the timeout period (set by running the usbclock –t:X command) at the set PWM duty (set by running the usbclock –p:X command). Pressing S1 again allows you to scroll through the different display modes of the clock. You can then see the date displayed on the clock as well as other settings. The display modes were shown in Table 2 last month. siliconchip.com.au Synchronising Your PC To A Network Time Server Fig.11: this dialog is used in WinXP to enable your PC to synchronise with an internet time server. T HE NTP (network time protocol) is used to synchronise “networkenabled” devices (such as your PC) with remote time-servers. Basically, a time-server is a server computer that derives its time from a very accurate reference clock and distributes this time to other computers. The most common time reference for these servers is a GPS clock or GPS master clock. To ensure that your PC’s local clock (and by extension, your USB clock) always shows the correct time, it’s necessary to enable NTP time synchronisation in Windows. When this is done, your PC will synchronise with the selected Internet time server once a week, although you can also perform manual updates as well. NTP synchronisation is enabled in Windows XP as follows: (1) Double-click the clock in the bottom right corner of the system tray. (2) Click the “Internet Time” tab on the resulting “Date and Time Properties” dialog to bring up the dialog shown in Fig.11. (3) Select “Automatically synchronize with an Internet time server”. (4) Enter a valid NTP server domain name into the space provided. The After the display timeout period expires (from the last switch press) the display mode will revert to the default display mode (set by running the usbclock –z:X command). The display timeout can be changed by running the usbclock –d:X command. There’s one more feature we need siliconchip.com.au Fig.12: if you have the firwall enabled on an ADSL or cable modem/router, then you will have to enable outgoing UDP connections on port 123. This screen grab shows the set-up for a Motorola SBG900 cable modem. au.pool.ntp.org server should work for users in Australia but you can also select one of the default overseas servers from the drop-down list. Alternatively, there are many other NTP servers available and you can easily do an internet search for them. A good place to start is www.pool. ntp.org (5) Click on the “Update Now” button to test the synchronisation. The Windows NTP service may fail if a firewall is blocking it, although NTP may also fail sporadically even when set-up correctly, due to lost packets or handshaking timing out. Punching through the firewall NTP uses UDP port 123, so you must ensure that your firewall is not blocking outgoing traffic on this port. If it is, NTP synchronisation will fail to explain and that’s the auto backlighting mode. If enabled (usbclock -a:1 or usbclock-a:2 turns it on, while usbclock -a:0 turns it off), the unit automatically turns the backlight on at the set PWM duty cycle, depending on the time of day (provided that the USB Clock is running on USB power). consistently and you will have to change the firewall’s settings. The Windows XP and Vista firewalls allow all outgoing traffic and will work by default. By contrast, other third-party firewalls often block out­ going connections on port 123 and will have to be modified. Do a search on the Internet to find the appropriate settings for your particular firewall (or check the manual). Note that you only need to enable outgoing UDP traffic on port 123 (not incoming). Similarly, if you have the firewall enabled on your ADSL (or cable) modem/router, then you may need to modify its settings as well. Fig.12 shows the settings for a Motorola SBG900 cable modem. Again, you only need to allow outbound UDP traffic on port 123. If in automatic backlight mode 1, the backlight will turn on between 6pm and 6am. This means that if you have the USB clock connected to a powered hub, the backlight will come on automatically at night. By contrast, in mode 2, it will be on all day. The auto backlighting will not work November 2008  37 Command Function Example Result The windows time will be synchronised with the USB clock. You will be able to see all the operating settings of the USB clock on your PC. An example screen shot is shown in Fig.10. usbclock or usbclock -s Synchronises the USB clock with the local clock on your Windows PC. usbclock usbclock -i View all relevant operating settings of the USB clock. usbclock -i usbclock -m:X where X is the number of one of the display modes in Table 2. Sets the PWM duty for the backlight. The higher the number the brighter the backlighting will be and the greater the power consumption. Note that for values below about 15%, the backlight will not be visible. Sets the timeout period in seconds for the backlight. When switch S1 is pressed the USB Clock will light the backlight. After the time-out period expires, the backlight dims to off. Sets the display time-out period in seconds. When this expires, the display reverts to the default display mode. Set the USB Clock’s display mode for the display time-out period. The clock then reverts to the default display mode. usbclock -v:X where X is in mV Sets the USB Clock’s reference voltage. usbclock -p:X, where X is a number from 0 to 100. usbclock -t:X usbclock -d:X usbclock -p:80 Sets the backlight PWM duty to 80%. usbclock -t:60 Sets the time-out period to 1 minute. usbclock -d:120 usbclock -m:0 Sets the display time-out period to 120 seconds (2 minutes). Sets the display mode to display the time in HH:MM (hours, minutes) format. usbclock -v:3300 Sets the reference voltage to 3.3V. the USB Clock’s sense resistor usbclock -c:X where X is in mΩ Sets value. usbclock -z:X where X is the Sets the USB Clock’s default display number of one of the display mode (and the display mode). modes in Table 2. usbclock -c:1650 Sets the sense resistor reference value to 1.65Ω. usbclock -l:X where X is in mV between 2170 and 4500mV. Sets the USB Clock’s low-voltage trip point. usbclock -l:2400 usbclock -a:X where X is either 0 (disable) or 1 (enable 6pm to 6am) or 2 (all day). usbclock -y:X where X is either 0 for 24-hour time (default) or 1 for 12-hour time. Sets the USB Clock’s auto backlighting on or off. usbclock -a:1 Sets the backlight to automatically turn on between 6pm and 6am. Sets the USB Clock’s time display mode (24hr or 12hr). usbclock -y:1 Sets the USB Clock to 12-hour time. usbclock.exe -r Resets the USB Clock. usbclock -z:1 usbclock.exe -r Making Usbclock.exe Run Automatically The USB Clock does not synchronise its time automatically with the PC just because it is connected to the PC via a USB cable. To do that, you have to run the usbclock.exe program (ie, by typing usbclock and pressing the Enter key at the command line). If you wish, you can automate this procedure by having Windows run usbclock.exe each time the computer boots up. This is done by placing a shortcut to the program in the Start-up folder, as follows: (1) Create a shortcut to the usbclock. exe program by right-clicking it and dragging it to the desktop. (2) Copy or move this shortcut to the C:\Documents and Settings\ 38  Silicon Chip YourUserName\Start Menu\Programs\Startup folder (YourUserName is your user account name). Once the above steps have been completed, the usbclock.exe program will automatically run each time Windows boots up and thus synchronise the USB Clock to the PC’s clock. Note that you should also set up your PC’s local time to synchronise automatically with an internet time server, to make sure that your PC’s clock (and thus your USB Clock) is always accurate. The way to do this is set out in a separate panel titled “Synchronising Your PC With A Network Time Server”. Sets the display to show the date. Sets the low voltage trip point to 2.4V. If it is set too high, the backlight will be turned off too soon. Resets the USB Clock and all settings are restored to default values. Table 4: the command line switches for the usbclock.exe host program. The USB Clock synchronises its time with your PC’s clock when you run this program without any switches and the program can also be set to run automatically when the PC boots. when the USB clock is running from battery power. In that case, you will have to turn the backlight on manually by pressing S1. Tweaking the charging current The charging current depends on the reference value for the sense resistor. If you wish, this reference value can be changed (to give a more accurate charging current readout) by running the usbclock -c:X command. The default value is 1.65Ω which is the nominal resistance of the two siliconchip.com.au How The Circuit Conserves Power One important feature of the PIC­ 18F4550 is its support for low-power managed modes. Although the use of CMOS ICs is important for minimising power consumption, much of the power conservation is achieved in the firmware Basically, the microcontroller will respond to interrupts and then go into idle mode, resulting in very low power consumption. In idle mode, peripherals like the screen refresh timer and the timekeeping timer still operate but the CPU is switched off. An interrupt generated by the peripheral will wake the CPU. The interrupt will then be serviced, after which the CPU reverts to idle mode again. In normal operation without the backlighting, the current consumption is less than 1mA. This means that the clock should be able to keep running from battery power for at least a few weeks before the batteries need recharging. By contrast, the backlight draws around 200mA at 100% duty-cycle. This reduces to around 100mA at 50% duty-cycle and 80mA at 30% duty-cycle. In battery mode, the backlight is turned on by briefly pressing S1. It will then stay on for the duration of the timeout period (this can be set by running the usbclock.exe program using the -t option, as explained below). After the period expires, the backlight quickly dims down and turns off. Note that the backlight duty cycle is also set by running the usbclock. exe program, this time using the -p option. In addition, as mentioned previously, the microcontroller automatically reduces the duty cycle if it detects that the supply voltage rail is buckling parallel 3.3Ω resistors on the PC board. If the resistors don’t measure 1.65Ω, you can tweak the reference value to match their actual value. Normally, however, you don’t need to worry about this unless you’re very fussy about accurate charging current readings. Similarly, the supply voltage reading depends on the accuracy of the 3.3V reference voltage. In practice siliconchip.com.au under the load (this will only happen when the backlight is used when running from battery power). Basically, the microcontroller sets a low-voltage trip point, with an interrupt occurring if the supply voltage drops below this point when S1 is pressed. When that happens, the microcontroller immediately reduces the PWM duty cycle of the backlight. As a result, if the batteries are sufficiently discharged, the backlight will not turn on when S1 is pressed. Going one step further, if the microcontroller detects that the supply voltage is below the trip point when the backlight is not being driven (ie, 0% duty-cycle), then the firmware will go into an extended power conservation mode (extra low power). In this mode, the main priority is to keep the real time clock updated, while the display will show “Lo” to indicate a low battery. The firmware will subsequently exit this mode when the USB clock is connected to a PC and the battery begins charging again. If the supply voltage drops even lower than this, the firmware assumes that power is soon to be lost or that the battery is too discharged to provide power. In this case, the firmware instructs the microcontroller to go to sleep. In this state, the CPU and all per­ipherals are turned off, markedly reducing the power consumption to just microamps. This prevents the battery from discharging even further. Of course, at this point, the timekeeping fails. However, it is subsequently synchronised the next time the USB clock is connected to the PC (provided the PC is operating). though, this may be slightly off due to manufacturing variations of IC1. It should be close to 3.3V and so the default value of 3.3V should be adequate in most cases. If necessary, you can change the reference voltage (using the usbclock -v:X command) to increase the accuracy of the voltage reading. It should match the voltage at pin 19 of IC1, as SC measured using a voltmeter. JOIN THE TECHNOLOGY AGE NOW with PICAXE Developed as a teaching tool, the PICAXE is a low-cost “brain” for almost any project Easy to use and understand, professionals & hobbyists can be productive within minutes. Free software development system and low-cost in-circuit programming. Variety of hardware, project boards and kits to suit your application. Digital, analog, RS232, 1-Wire™, SPI and I2C. PC connectivity. Applications include: Datalogging Robotics Measurement & instruments Motor & lighting control Farming & agriculture Internet server Wireless links Colour sensing Fun games Distributed in Australia by Microzed Computers Pty Limited Phone 1300 735 420 Fax 1300 735 421 www.microzed.com.au November 2008  39