Wednesday, August 26, 2015

New progress today - ESP8266 has UNIX CRON functionality

I've added a cron functionality to my ESP8266 and is working great.
Now I can send a JSON string with unix like cron command:

{"device_name":"ESP9191919", "type":"my_isp_type", "minute":"22" , "hour":"10", "day_of_month":"26", "month":"7", "day_of_week":"3", "gpio":"14","duration":"20", "skip":"0","status":"1", "action":"add" }

to setup a cron job on a specific GPIO. I need it for my irrigation system that was using a CRON on  a raspberry PI to receive the commands for valves.

My CRON implementation support now the "*" functionality for minute, hour, day_of_month, month and day_of_week. In this version is not supporting the "*/10" functionality but if I will need it I will do it.

So sending once the JSON :

{"device_name":"ESP9191919", "type":"my_isp_type", "minute":"00" , "hour":"22", "day_of_month":"*", "month":"*", "day_of_week":"*", "gpio":"14","duration":"20", "skip":"0","status":"1", "action":"add" }

will start the valve connected to gpio 14 every day at 22:00 for 20 minutes.

If I want to skip this cron 2 days, I need to send the same JSON but with skip value of 2.

Skip value get automatically decremented and when it has the value of 0 the cron will do the job. I've need it this functionality, because finally the ESP will be an autonomous system, getting the data from Internet and from my yard, and will be able to propose me an watering plan ( in first stage to be able to test it) and finally to be able to take decisions by itself.
This is what IoT means. 

If I want to disable this cron job, I need to set the status to "0" so it will be ignored every time.

I could have also added the year as a parameter (have it but not used), but I didn't find any utility for that. But is an easy job to do it.

The important thing is that the cron data is written in the flash so a power down is not affecting the cron functionality.

Writing to flash was minimized so only if is necessary a flash update will be done. 

I've used sector 2 for storing the cron data so I can have like 400 cron jobs for now, which is enough for now. I guess I can squeeze another 1000 records in the other sectors, but for now 400 are enough.

TODO list:

Export data as JSON:
  •   {"cron_data":{"minute":"2","hour":"16",......},{"minute":"15","hour":"9",......},   {"minute":"44","hour":"12",......}, {"minute":"20","hour":"8",......}}    DONE !!!
  • */5 functionality 
  • continuity for cron jobs - if there is a power down during a cron job, continue from where it left.


  1. Hi Catalin, sounds like a very useful capability to have on an ESP. I have looked around your blog but do not see code for this anywhere. Do you have code available? And did you write it in C or Lua? Thanks!! Jay

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  3. Thanks for your blog - I have a '201 board coming and you have saved me a bunch
    of time.
    I would also love to see your 'cron' code IF it's available.

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