HC-05 Bluetooth module sleep after 5 secs idle

[iMo]

It is 10 years back I first time asked on this less known "issue" (afaik on arduino forum and perhaps on stm32duino too) - thus it could be somebody found a solution in the meantime 

Module is the slave, paired, everything works fine, I've been using several modules with lot of boards for a decade already.

Now the "issue" - when there is none TX activity via serial (via the wire connected to an mcu) for more than 5 seconds, the module enters a "sleep mode". That is great, as the current consumption drops from 20mA to 2mA.

In order the wake up the module from the sleep, you have to either send a char from the host PC (via the air), or, send a char via the TX wire (off the mcu). Ok, that is how it should work..

BUT - the wake up takes some rather long time (at least that is my understanding), thus when you for example send a 100 char long message at 115k2 every 6 seconds, the first 20-30 chars of the message get simply lost.

In order to disable the "sleep" I did mess in past with some crazy settings I saw in various versions of the DS I randomly tried with none result.

Perhaps somebody knows a trick how to change/disable the "sleep" setting in the lovely HC-05 module?

[eutectique]

What does AT+SNIFF? return ?

[iMo]

Here it is - it looks like as a pretty ancient firmware..

Code: [Select]

AT+VERSION?
+VERSION:1.0-20090818
OK
AT+IPSCAN?
ERROR:(1)
AT+STATE?
+STATE:INITIALIZED
OK
AT+SNIFF?
ERROR:(0)
AT+UART?
+UART:115200,0,0
OK
PS: I've been dealing with the issue in an app such I send a char (ie. "+" as my first item in the record is a positive number) and wait 50ms. When the mcu sends data within 5secs I get +1234, when the period is more than 5secs I get 1234. Quite a naive workaround but at least it works..

PPS: even so I get from time to time a "+" when the period is >5secs. It seems when the module is in sleep, it depends whether you fit exactly with the first character in a slot when the module is sniffing or not.

[eutectique]

IMO, the cleaner way would be to read the module state (AT+STATE?) and send only if it is in the proper state. This command will also wake the module up.

If you want to keep the module awake, but AT+EXSNIFF is not implemented, just send AT+STATE? every two seconds or so.

[iMo]

That is "extremely" complicated. In order to enter the AT mode you have to set pin34 to high and power the module off/on. Then you have to switch the mcu baudrate in 38k4, do the AT stuff, then go back into Data mode in a similar way and also switch mcu into 115k2 I've been using.