Software control power ON

I should like a very low power watch battery powered power on/off switch that would power on my Pi Zero a certain time (say 20 min or 60 min) after it last switched off.
I could then send a software comand – ‘turn off for 60 mins’ – and power consumption would fall to zero for 1 hour then it would restart.

The particular application is for a GPS device: if after being powered back on, its next GPS fix showed that it had not moved, then it would power off again. Also once stationary for 10 mins, it would power off for 10 min. Hence it would only stay on whilst moving.

Another application for such a device would be an alarm clock. I do have a watch battery voltage output from a GPS device (which would look after recharging the battery etc.).

Any ideas please?

Is the Witty Pi any use?

+1 for the Witty Pi. I have the first gen one and it has worked great. You’d need to configure it in Linux first, I think, but after that I’d assume it wouldn’t care what OS you boot into. I can’t say I’ve ever tried it with RISC OS though.

I’ll try it – many thanks. The second gen one no longer uses TXDATA (which is good as that would confuse the GPS module) and its IIC address is &68 which is different from the OLED display (&78 or &7A I thought but perhaps it is &3C) and the 16×2 text display (&27). It looks like I shall have to see what Linux is doing – utilities written in BASH which is probably similar to BASIC or command line – and then work out how to express the same in RISC OS.

which is different from the OLED display (&78 or &7A I thought but perhaps it is &3C)

If you mean my OLED, yes, it is device &3C.

Witty Pi version 2 uses a RTC clock chip (3231) similar enough to the 1337 that it ‘just works’.

I have a project which requires a software command to turn off the computer with a scheduled restart time (for the moment 10 mins hence). I have a model A+ plus a Witty Pi and the following BASIC programme which reads the RTC chip time (via IIC) and sets an alarm 10 mins hence (which schedules the machine to be turned on again in 10 mins time). It then waits for you to press the space bar. Once the SPACE bar is pressed, it asserts GPIO 4 low using the GPIO module (which the Witty Pi sees as a command to turn off):

   10REM >GPIO_Off
   20REM Reads RTC time etc. from DS3231SN clock chip on Witty Pi 2
   30gpio%=TRUE
   40LOCAL ERROR
   50ON ERROR LOCAL gpio%=FALSE
   60IF gpio% THEN *RMEnsure GPIO 0.63 Error GPIO Module not present
   70RESTORE ERROR
   80:
   90DIM mem% 32 , iic% 48 , dow$(7) , mth$(&12)
  100mth$()="???"
  110dow$(0)="???"
  120dow$(1)="Sun"
  130dow$(2)="Mon"
  140dow$(3)="Tue"
  150dow$(4)="Wed"
  160dow$(5)="Thu"
  170dow$(6)="Fri"
  180dow$(7)="Sat"
  190mth$()="???"
  200mth$(1)="Jan"
  210mth$(2)="Feb"
  220mth$(3)="Mar"
  230mth$(4)="Apr"
  240mth$(5)="May"
  250mth$(6)="Jun"
  260mth$(7)="Jly"
  270mth$(8)="Aug"
  280mth$(9)="Sep"
  290mth$(&10)="Oct"
  300mth$(&11)="Nov"
  310mth$(&12)="Dec"
  320:
  330!iic%=&20D0:REM write chip reg address (00)
  340iic%!4=mem%
  350iic%!8=1
  360?mem%=0
  370iic%!12=&20D1:REM read from that chip register onwards
  380iic%!16=mem%+4
  390iic%!20=16:REM read all 16 time & alarm registers
  400SYS "OS_IICOp",iic%,2
  410:
  420REM Decode RTC registers
  430IF (mem%?6) AND &40 THEN
  440  REM 12 hour
  450  IF (mem%?6) AND &20 THEN
  460    REM pm
  470    a$=RIGHT$("00"+STR$~((mem%?6) AND &1F),2)+":"+RIGHT$("00"+STR$~(mem%?5),2)+":"+RIGHT$("00"+STR$~(mem%?4),2)+"PM"
  480  ELSE
  490    REM am
  500    a$=RIGHT$("00"+STR$~((mem%?6) AND &1F),2)+":"+RIGHT$("00"+STR$~(mem%?5),2)+":"+RIGHT$("00"+STR$~(mem%?4),2)+"am"
  510  ENDIF
  520ELSE
  530  REM 24 hour
  540  a$=RIGHT$("00"+STR$~(mem%?6),2)+":"+RIGHT$("00"+STR$~(mem%?5),2)+":"+RIGHT$("00"+STR$~(mem%?4),2)
  550ENDIF
  560:
  570b$=dow$(mem%?7)+","+STR$~(mem%?8)+"-"+mth$((mem%?9) AND &1F)
  580b$+="-2"+CHR$(((mem%?9)>>>7) OR &30)+STR$~(mem%?10)+"."
  590:
  600REM 11-sec 12-min 13-hrs 14-DATE
  610IF (mem%?13) AND &40 THEN
  620  REM 12 hour
  630  IF (mem%?13) AND &20 THEN
  640    REM pm
  650    aa$=RIGHT$("00"+STR$~((mem%?13) AND &1F),2)+":"+RIGHT$("00"+STR$~(mem%?12),2)+":"+RIGHT$("00"+STR$~(mem%?11),2)+"PM"
  660  ELSE
  670    REM am
  680    aa$=RIGHT$("00"+STR$~((mem%?13) AND &1F),2)+":"+RIGHT$("00"+STR$~(mem%?12),2)+":"+RIGHT$("00"+STR$~(mem%?11),2)+"am"
  690  ENDIF
  700ELSE
  710  REM 24 hour
  720  aa$=RIGHT$("00"+STR$~(mem%?13),2)+":"+RIGHT$("00"+STR$~(mem%?12),2)+":"+RIGHT$("00"+STR$~(mem%?11),2)
  730ENDIF
  740:
  750bb$=STR$~(mem%?14)+"th"
  760:
  770PRINT "RTC time is: ";b$;a$
  780PRINT"Alarm time is: ";bb$;aa$
  790:
  800PRINT"Setting alarm 1 to current time plus 10 minutes"
  810REM Use mem%+4 (sec) +5 (min) +6 (hr) +8 (date)
  820REM from chip registers 00 to 02 and 04 and add 10min
  830REM and write to registers 07 to 0A (alarm 1)
  840mem%?5=(mem%?5)+&10
  850mem%?7=mem%?8
  860!iic%=&20D0:REM write 4 bytes to chip reg address (07)
  870iic%!4=mem%+3
  880iic%!8=5
  890mem%?3=7
  900
  910iic%!12=&20D0:REM write 1 byte to chip reg address (0E)
  920iic%!16=mem%+9
  930iic%!20=2
  940mem%?9=14
  950mem%?10=5:REM enable alarm 1 plus interrupt (to turn Pi ON
  960REM when alarm activates)
  970SYS "OS_IICOp",iic%,2
  980:
  990!iic%=&20D0:REM write chip reg address (00)
 1000iic%!4=mem%
 1010iic%!8=1
 1020?mem%=0
 1030iic%!12=&20D1:REM Read from that chip register
 1040iic%!16=mem%+4
 1050iic%!20=16:REM read all 16 time & alarm registers
 1060SYS "OS_IICOp",iic%,2
 1070:
 1080REM Decode RTC registers
 1090IF (mem%?6) AND &40 THEN
 1100  REM 12 hour
 1110  IF (mem%?6) AND &20 THEN
 1120    REM pm
 1130    a$=RIGHT$("00"+STR$~((mem%?6) AND &1F),2)+":"+RIGHT$("00"+STR$~(mem%?5),2)+":"+RIGHT$("00"+STR$~(mem%?4),2)+"PM"
 1140  ELSE
 1150    REM am
 1160    a$=RIGHT$("00"+STR$~((mem%?6) AND &1F),2)+":"+RIGHT$("00"+STR$~(mem%?5),2)+":"+RIGHT$("00"+STR$~(mem%?4),2)+"am"
 1170  ENDIF
 1180ELSE
 1190  REM 24 hour
 1200  a$=RIGHT$("00"+STR$~(mem%?6),2)+":"+RIGHT$("00"+STR$~(mem%?5),2)+":"+RIGHT$("00"+STR$~(mem%?4),2)
 1210ENDIF
 1220:
 1230b$=dow$(mem%?7)+","+STR$~(mem%?8)+"-"+mth$((mem%?9) AND &1F)
 1240b$+="-2"+CHR$(((mem%?9)>>>7) OR &30)+STR$~(mem%?10)+"."
 1250:
 1260REM 11-sec 12-min 13-hrs 14-DATE
 1270IF (mem%?13) AND &40 THEN
 1280  REM 12 hour
 1290  IF (mem%?13) AND &20 THEN
 1300    REM pm
 1310    aa$=RIGHT$("00"+STR$~((mem%?13) AND &1F),2)+":"+RIGHT$("00"+STR$~(mem%?12),2)+":"+RIGHT$("00"+STR$~(mem%?11),2)+"PM"
 1320  ELSE
 1330    REM am
 1340    aa$=RIGHT$("00"+STR$~((mem%?13) AND &1F),2)+":"+RIGHT$("00"+STR$~(mem%?12),2)+":"+RIGHT$("00"+STR$~(mem%?11),2)+"am"
 1350  ENDIF
 1360ELSE
 1370  REM 24 hour
 1380  aa$=RIGHT$("00"+STR$~(mem%?13),2)+":"+RIGHT$("00"+STR$~(mem%?12),2)+":"+RIGHT$("00"+STR$~(mem%?11),2)
 1390ENDIF
 1400:
 1410bb$=STR$~(mem%?14)+"th"
 1420:
 1430PRINT "RTC time is: ";b$;a$
 1440PRINT"Alarm time is: ";bb$;aa$
 1450:
 1460IF gpio% THEN
 1470  REM Set pin 4 TO OUTPUT high
 1480  SYS "GPIO_ReadOE",4 TO pin4%
 1490  IF pin4%=0 THEN PRINT "Pin 4 is currently an output"
 1500  IF pin4%=1 THEN PRINT "Pin 4 is currently an input"
 1510  SYS "GPIO_WriteData",4,1:REM Set pin 4 to HIGH
 1520  SYS "GPIO_WriteOE",4,0:REM set pin 4 to output
 1530  PRINT "Press SPACE bar to turn computer OFF and it will then"
 1540  PRINT "turn on when alarm 1 goes off"
 1550  REPEAT
 1560    IF INKEY(-99) THEN SYS "GPIO_WriteData",4,0 ELSE SYS "GPIO_WriteData",4,1
 1570  UNTIL 0
 1580ELSE
 1590  PRINT "GPIO module not present"
 1600ENDIF
 1610END

there seem to be a few idiosynchrasies – the day of the week is not set when you set the time for example, but it does work. The chip is sufficiently similar to the DS1337 and DS1338 that it is supported by the RISC OS HAL. The only issue at present is that after it schedules itself to turn on, it seems to lose the time and date setting. This may be due to it setting an erroneous alarm time (minutes sixty-something) so more investigation needed…