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Poorman's monostable 555, but without a 555 chip. Allows circuit to remain powered for a set amount of time after circuit is turned off. Not an ideal solution...but if you don't have a 555 chip, but you do have 2x transistors, some resistors, and a capacitor you can create the circuit.
Press and release the push button in the upper left of the circuit to start. Notice LED remains lit for a little while after push button is off.
Increase the capacitance of the 10uF capacitor in the lower left of the circuit to increase the time the circuit is powered. Decrease capacitance to decrease the time.
I used this circuit for an ESP8266 wifi enable microcontroller and 9V battery attached to my mailbox (in an enclosure and sensor). Opening the mailbox closes the circuit and powers the ESP8266 long enough for it to connect to my house's wifi and send a push notification to the Pushsafer App (iOS, Android, etc), letting me know my mail has arrived. Regardless of how fast the mailman can open and close the mailbox door, the circuit will be powered long enough to send the message.
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