A solenid latch to contract and release a door after a set amount of time, that is being pulled by a spring to open it.

This is the concept I was thinking of (though the oscillator counter is the 4060, not 4020... )



Concept:
The two gates at the top left form a set-reset latch. In the idle state, the output of the lower gate is high, holding the 4060 in reset. From the datasheet, that may also tristate the oscillator driver, so current next to zero overall.

Pressing the start button sets the latch upper gate output high & lower one low, allowing the 4060 to start counting.

The Q outputs will count up, Q4 first going high after 8 osc cycles, Q10 after 512, through to Q14 going high after 4096 cycles.

20 minutes is 1200 seconds, so with Q14 connected to R4 and the oscillator at around 3.4Hz, it should give a 20 minute delay before Q1 is switched on, pulling 4093 pin 9 low.

The lower two 4093 gates form a monostable multivibrator.

When pin 9 goes low, pin 10 goes high and pins 12 & 13 are pulsed high by C4.
In turn pin 11 goes low, turning on the solenoid driver and pulling pin 8 low, holding the monostable active.

Once C4 discharges through the preset pot - which controls the duration of the solenoid pulse - the monostable resets.

When the output at pin 11 goes low, it also resets the SR latch, resetting the 4060 until the button is pressed again.

Once the monostable has timed out, everything goes back to its low power state soon afterwards.

[IF I've not made any mistrakes!!!]

Caution , solenoid DCR is the only thing limiting current thru Q2.

Regards, Dana.

danadak said:

Caution , solenoid DCR is the only thing limiting current thru Q2.

Regards, Dana.

Click to expand...

If it is a 12v solenoid, then that is pretty much how they work. I didn't look, but the latch should generally be released within one second or so to prevent heating and battery drain.

It is a concept drawing, without knowing the solenoid power. If the solenoid needs more than 100 - 200mA, Q2 could be changed for a PNP darlington with suitable ratings.

The solenoid pulse duration is limited by the C4 & VR2 etc. time constant.

ZipZapOuch said:

The options given are pretty power hungry.
- How long do you want your batteries to last? Days, weeks, months, years?

- How often will the device be activated? One per hour, day, week, ...

- are the batteries inside or outside of the box? That is, if the batteries fail, will there be a way to access inside of box?

- Do you have info on the specific solenoid latch you plan to use? Current draw and recommended time to trigger are most important.

Click to expand...

the batteries dont need to last more than a day. the device will not be activated on an on-going basis. its supposed to be operational for one day. the batteries can be anywhere. if the batteries fail, yes, the batteries could be accessed. No I have no specific solenoid latch in mind. the goal here is to be able to open the door with a timer. please let me know if I answered all your questions

digandug said:

Thank you so much. This is great information.

Click to expand...

Dana
Thanks again for your help. The image you shared is an Arduino UNO. Right? I'm thinking Arduino is the best option.
And block programming seems easy

Image in post #8 is a Nano board.



Regards, Dana.