NT-250 Web Server
Device configuration help

This page is not complete user manual, but will explain some settings, whose configuration is not so obvious.


Ethernet module

This option allows you to configure how the Ethernet module is used by the system. There are case, where the module can be turned off, and so to reduce the heat dissipated from the chip and significantly to reduce its power consumption. For example, when the device is used in stand-alone mode and displays the time from the onboard hardware clock, or when the ethernet cable is disconnected for a long period of time, the module can be turned off.

Enabled: the ethernet module is always on.

Disabled: the ethernet module is always off.

Automatic: the module is on while an ethernet link is present, and is automatically shut down when the link disappears for more than 10 seconds. Then, on every 3 minutes the module is powered on and the link is checked. If a link is present, the module stays on until the link disappears again for more than 10 seconds. If no link is present, the module is powered down and checked again after 3 minutes.

Note: At any time when the module is disabled, you can enable it immediately by pressing shortly (< 1 sec) the button at the back of the device. However, if there is no link present, the module will be automaticaly powered down after 10 seconds.

Note: If the Ethernet mode is set to "Disabled", but the NTP service is enabled, then every night at 00:00 (or 01:00 if DST is active) the module will be enabled, allowing the onboard clock to synchronise with the NTP server and so to maintain best clock accuracy. After successful sync or if there is no link present, the module will be disabled again. If you don't want this behaviour, disable the NTP service.


Display mode

This option determines how the device will display the current time.

Remote server: time is obtained from the remote server only.

Onboard clock: time is obtained from the onboard hadrware clock only.

Combined: whenever a connection with the remote server is established, the time will be obtained from it. If the connection gets lost or there is no ethernet link, the time will be obtained from the onboard clock.

Note: The connection is considered to be lost when more than 90 seconds has passed since the last update.


This option allows you to configure the brightness of the display. You should use the smallest value, which makes the display comfortable to look at. Manual mode can be used in places, where the ambient light is constant or changes insignificantly. In all other cases, automatic mode should be used.

When "Automatic" mode is selected, 3 additional fields will appear:

Sensitivity: this option controls how sensitive the ambient light sensor is. The measured value from the sensor is multiplied by this value. If the brightness changes significantly with small changes of ambient light, decrease this value. If the brightness is insufficient for the current ambient light, increase the value.

Min value: this is the lowest value, below which the brightness won't decrease, no matter the ambient light.

Max value: this is the highest value, above which the brightness won't increase, no matter the ambient light.

Note: For the Min and the Max fields the range is 2 ÷ 255, where 2 is the lowest possible brightness, 255 is the highest. For the Sensitivity field the range is 0.2 ÷ 2.55, where 1 is the default value.

Date & Time

Clock offset

The accuracy of the onboard hardware clock can't be perfect and depends on many factors, such as ambient temperature, crystal's tolerance, supply voltage etc. To compensate these factors, an offset value can be set, which can increase the accuracy of the clock to 1÷4 seconds per month.

To calculate the clock offset value, use the following equation: offset = ΔT / 0.375, where ΔT is the clock deviation in seconds per 24 hours. Round the result to the nearest integer. Set positive offset if the clock runs faster, negative if it runs slower.

Note: The longer the measurement interval is, the more accurate calibration can be achieved. For example, measurement of time deviation for 48 hours is better than 24, and 72 is better than 48.

Example: the measured deviation for 48 hours is +4 seconds, e.g. when the real time is 8:00:00, the clock displays 8:00:04. Since this deviation is for 48 hours, we divide it by 2 and the result is 2 sec / 24h. Now, using the equation above gives us:

2 / 0.375 = 5.333

5.333 rounded to the nearest integer is 5. Since the clock runs faster, set +5 value for the offset field.

If the real time is 8:00:00, but the clock displays 7:59:56 (time deviation -4), using the same equation will results 5 again. But since the clock runs slower, set -5 for the offset value.

Now the question is, how accurate will be the clock after this calibration? The required value is 5.333, but since we can't use fractional numbers, 5 will be used instead. Since 1 unit is 0.375 sec / 24h, we have to multiply the reminder (0.333) with this number and then multiply it by multiples of 24 to determine the real accuracy for a week, month or a year:

0.333 * 0.375 = 0.125 sec / day
0.125 * 7 = 0.875 sec / week
0.125 * 30 = 3.75 sec / month
0.125 * 365 = 46 sec / year

Please note that these calculations would be correct only if the clock deviation is measured correctly. Since this is not always possible, further adjustments of the offset value may be needed for better accuracy. However, well calibrated clock with enabled NTP service can guarantee, that at any time the clock is as accurate as 0.1 - 0.2 sec.

Note: Setting positive values when the clock runs faster, and negative when it runs slower may sounds confusing, but in fact, when the clock runs faster, the period of a single impulse from its generator is shorter than needed, and thus it has to be increased. And when the clock runs slower, the period is longer than needed, hence it has to be decreased.