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I'm creating a cheap room escape in a box. The housing box has hidden doors and the Raspberry Pi inside should be able to open them at will.

I've seen people using servos to open the thing, electromagnets to release the piece of wood, solenoids to push it out of place. But I don't have any practical experience to know which will be simplest and cheapest for me to implement. Anything that can open the door/drawer/piece of wood is good for me.

Question is: which technology should I investigate further for this function? Thanks

TonyM
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javirs
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  • to let u know I have easy access to 0-5V, to 0-3.3V, to DIO, i do not have easy access to analogical input, I'm somehow defining the framework I'm working in. – javirs May 29 '17 at 08:10
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    @FakeMoustache, to show the level of control and communications available to as-yet-unknown technology, of course. How obvious is that. Don't try to rephrase the question. Don't demand more detail of other OPs then less detail here on a whim. This is just you tediously whining; be constructive or be quiet. – TonyM May 29 '17 at 08:16

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I have used an all-in-one door lock/catch consisting of a solenoid and a push-to-lock type catch. Search the Internet for 'door lock electric' and you'll see examples of these.

You then need a solenoid driver. There are plenty of cheap modules available to drive your solenoid from a logic output. Make sure you put a pull-down resistor on the Raspberry Pi I/O driving it. This is so the solenoid doesn't false-trigger on power-up when the I/O pin is not yet configured as an output. Make sure you connect a reverse-biased 1N4007-or-similar diode across the solenoid coil to discharge the back-e.m.f. current when the solenoid is switched off.

The problem is does leave you with is stopping your software turning the solenoid on and leaving it on, overheating the coil, possibly dangerously so. Perfectly behaved software won't do this, nor will software using a watchdog timer correctly and reliably. Both of these don't get written very often (despite their author's beliefs).

I would solve this safety problem in hardware by having the software trigger a timer circuit that cannot be retriggered. This would generate a simple sequence: solenoid powered for (e.g.) 100 ms then solenoid off for (e.g.) 2 sec. Faulty software constantly triggering this circuit would only put a 5% duty cycle on the solenoid.

TonyM
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You definitely need some actuation to realize this system. Most of the locking mechanism are based on solenoid and modules are widely available.

If you need to implement a 12v module along with raspberry pi, then other parts needed will be 12v to 5v buck converter, MOSFET to drive the solenoid load from 3.3v Pi output. A 12v power supply adapter could power the whole system.

Alternatively, if you need to use a battery, then consider using a boost converter to power up the solenoid.

Prasan Dutt
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  • will this: https://www.amazon.es/dp/B06XD6Q746/ref=sr_1_1?ie=UTF8&qid=1496046490&sr=8-1&keywords=rele+5v be a valid example to control something like this : https://www.amazon.es/12V-Electroim%C3%A1n-Solenoide-Bastidor-Abierto/dp/B00ICD1OL6/ref=sr_1_2?ie=UTF8&qid=1496046146&sr=8-2&keywords=solenoide ???? – javirs May 29 '17 at 08:46
  • Relay is good option (but suitable for AC switching) if you don't have any circuit design experience. It would be like using a crane to lift a bicycle. A MOSFET can do the switching for you, look at this link: https://electronics.stackexchange.com/questions/29065/how-to-control-a-12v-solenoid-valve-with-a-mosfet – Prasan Dutt May 29 '17 at 08:51
  • having no experience with mosfet and inverted diode and it all .. can I use the block in my old comment to send a signal (3.3v or 5v via transistor) to the device and forget about everything? furthermore it is opto-coupled and the inner perks of the e.m.f are handled for me. Is that a valid approach? Prize is also pretty nice (I know a mosfet is cheaper, but my time also costs) – javirs May 29 '17 at 09:05
  • Yes, relay module with opto isolation is good to go if you don't have any size restrictions. Further, let me know if you're looking for freelancer for outsourcing your work as time is crucial for you. – Prasan Dutt May 29 '17 at 09:14