Schematic errors and fewer failure modes

A project log for Nerdfeeder

Simple, inexpensive and dispenses peanuts in exchange for dropping stuff in a hole.

Stephen ChaseyStephen Chasey 05/19/2022 at 09:030 Comments

Ok, fixing another error in the schematics (PIR-triggered on/off 555 monostable) and made an improvement. Adding a diode from the 555 reset to the trigger will discharge the timing capacitor even if the output is high. 

Before, the PIR would power on the circuit for ~90 sec and then turn off. The PIR would have to be triggered again after output goes low. 

This could lead to two failure modes:

  1. bird drops item just before the timer is up and the circuit shuts down before a nut is dispensed
  2. bird drops item just as the timer is up and the item is not detected

Adding the diode from pin 6 to pin 2 on the 555 means the timing cap is discharged a bit when the trigger is pulled to ground, adding time to the cycle and keeping the sensors on as long as the PIR gets triggered during the cycle. This avoids the above failure modes.