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imp.deepsleepuntil(hour, minute, second, day)

Puts the imp into deep sleep until the specified time




Name Type Description
hour Integer The wake-up hour in 24-hour format (midnight = 0)
minute Integer The wake-up minute (0—60)
second Integer Optional, the wake-up second (0—60, default = 0)
day Integer Optional, the day of week on which to wake (0—6, default = any)




This method causes the imp to disconnect from the current network interface, enter a very low power mode (‘deep sleep’) and stop executing code until the specified time of day, expressed in UTC using 24-hour notation. The imp will also wake, superseding this call, if the wake-up pin has been set and is subsequently triggered.

Note This method is very similar in operation to server.sleepuntil(). However, unlike server.sleepuntil(), imp.deepsleepuntil() does not perform a server.flush() operation to ensure that any pending messages are sent before sleep.

When the imp enters deep sleep, the execution of Squirrel code is stopped entirely. When the imp wakes up, its device code is loaded from its flash storage and restarted. No state data is preserved, with the exception of the special nv table, which will be maintained. The nv table is not preserved through a power-cycle.

In deep sleep, all of the imp’s pins are tri-stated, unless you have enabled its wake-up pin. The wake-up pin (and only the wake-up pin) has a weak pull-down.

Optionally, the day of the week can also be given, which means this function can cause the imp to go into deep sleep for up to a week. The imp API provides numeric constants for SUNDAY through to SATURDAY, enumerated from 0 to 6. These values are consistent with Squirrel’s date() function, which returns a table where the wday field is the number of days since Sunday. This means that no normalizations have to be done in the Squirrel code.

Constant Value

If no day of the week is given — only three parameters are passed — then the wake-up matches any day of the week, ie. the disconnection can last a maximum of one day.

Deep sleep mode draws approximately 6μA of current on the imp001 card, or 4μA on imp modules (the imp005 does not support deep sleep). The processor is effectively shut down. Upon waking from deep sleep, the device will be in a ‘warm boot’ state with code execution returning to the start of the script. Booting and reconnecting to the network will take a second or more, so this method may not be appropriate for very short sleep periods.

It is recommended practice to call imp.deepsleepuntil() only when the imp is idle, ie. when impOS is ready for this to take place. This is best achieved by incorporating your imp.deepsleepuntil() code inside a function that is registered to called when the imp goes idle. To do so, use the method imp.onidle():

imp.onidle(function() {
    imp.deepsleepuntil(0, 0);

Note Using imp.wakeup() as an alternative to imp.onidle() is not recommended in this case, as any timeout provided can be no guarantee that the imp has become idle at that point. imp.onidle() is on the only way to be sure.

Module-specific Information


This method is not available on imp003-based devices with no 32kHz crystal.


This method is not available on imp004m-based devices with no 32kHz crystal.

You will not be able to preserve data in the nv table during sleep: the imp004m does not implement nv table functionality. Please see Designing Hardware with the imp004m for workarounds.


imp005 devices are not currently capable of deep sleep, so imp.deepsleepuntil() has been removed from the imp005. Calling this method on an imp005 will cause an exception to be thrown.

Example Code

This example wakes the imp up for about 0.05 seconds each minute to do some data logging. Once an hour it also fires up WiFi and dumps that hour’s readings to the server. Once DHCP and so on are taken into account, the hourly wake-up can last for several seconds. This technique enables the imp to use only tiny amounts of power overall which is useful when running from a battery.