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| Title | Trigger an event at 5, 10, 15, ... minutes after the hour. |
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| Keywords | alarm, hourly |
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| Categories | Controls |
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Use a Timer. When the Timer fires, calculate the next time to fire the alarm and then set the timer's Interval property to either 60000 or the time it needs to wait, whichever is smaller.
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Private Sub tmrAlarm_Timer()
Static next_alarm As Date
Dim secs_to_go As Single
' See if we have initialized next_alarm.
If next_alarm = 0 Then
' Initialize next_alarm.
next_alarm = NextAlarmTime
lblNextAlarm.Caption = Format$(next_alarm, _
"hh:mm:ss")
End If
' See how many milliseconds until the next
' alarm time.
secs_to_go = DateDiff("s", Now, next_alarm)
' Stop the timer to clear previous alarms.
tmrAlarm.Enabled = False
' Set the timer's Interval.
If secs_to_go < 1 Then
' Fire the alarm.
' *** Do something here ***
Beep
' Reinitialize next_alarm.
next_alarm = NextAlarmTime
ElseIf secs_to_go < 60 Then
tmrAlarm.Interval = secs_to_go * 1000
Else
tmrAlarm.Interval = 60000
End If
' Restart the timer.
tmrAlarm.Enabled = True
End Sub
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The helper function NextAlarmTime calculates the next alarm time. It gets the current time in hours and minutes and then uses some math to calculate the next multiple of 5 minutes.
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' Return the next time that is a multiple of 5 minutes.
Private Function NextAlarmTime() As Date
' The number of minutes between alarms.
Const ALARM_INTERVAL = 5
Dim time_now As Date
Dim h As Integer
Dim m As Integer
Dim seconds As Long
Dim next_m As Integer
' Get the current time.
time_now = Now
' Get the hour and minutes.
h = DatePart("h", time_now)
m = DatePart("n", time_now)
' Calculate the next multiple of ALARM_INTERVAL.
next_m = ((m \ ALARM_INTERVAL) + 1) * ALARM_INTERVAL
NextAlarmTime = DateAdd("n", h * 60 + next_m, Date)
End Function
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My book Custom Controls Library includes an Alarm control that lets you set alarms far in advance. It demonstrates general techniques for building timer ActiveX controls.
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