I am a Newbie and I do not have a lot of expirience. The circuit has been put together from pieces I have found on the internet. My goal is to develop a reliable wireless solenoid circuit to water my tomato plants on my balkony.

The circuit I have developed so far. https://easyeda.com/editor#id=b929cf452b52475bb0b40aca272a42e8.

In order to make the circuit failsafe, I came up with the following idea:

  • Circuit turns on, valve is closed, watchdog is disabled
  • ATTiny85 receives periodic PING from Master station
  • First PING will enable watchdog
  • ATTiny85 sends periodic heartbeat to watchdog for each subsequent received PING
  • Missing heartbeat/PING will reset the microsontroller and close the valve

I would really appreciate if someone from the community could look over the design and let me know how to improve the circuit and if above approach is OK to avoid a permanent open valve.

  • \$\begingroup\$ It looks like your 555 timer, your choice of C8 and R9 is dependent on what you want your duty cycle to be for the chip... so that needs to be a decision you need to make. I did not see an R6 but I'm assuming you mean R5 instead. For R5, you should review the electrical specifications and see if you can find anything about the RESET. \$\endgroup\$ – KingDuken Apr 5 '19 at 21:15
  • \$\begingroup\$ Thanks for your comment. After reading the datasheets again I have realised a big design mistake and I had to remove the timer circuit and to replace the watchdog. \$\endgroup\$ – Cage Apr 6 '19 at 11:47

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