8 replies to this topic

[WahidM]

Hi, I am very new to the world of electronics but have solid .net experience, so please excuse my lack of knowledge on this. Right, i have been asked to build a project that will allow a mobile device to connect to a board (in this case the netduino) via either USB, Bluetooth or serial which will send an authentication code. The netduino will authenticate the code (basic algorithm) and then release a electromagnectic door lock. I need to then check to see when the door has been closed and a message back to the connected mobile device via the USB, Bluetooth or serial. I have no idea what so ever as to what kit i will need, so i need some expert help. I can pick up the programming side but i dont know what hardware will get this solution of the ground. Any help would be appreciated. Thanks, Wahid

[Binu]

Whats the mobile device you gonna use, since most of the mobiles wont allow to access the USB. You can go for bluetooth or wifi for communicating with the mobile phone. You can connect the lock to the netduino through a driver, which depends upon the current rating of the lock.

[Mario Vernari]

Hello Wahid, and welcome to the Netduino world. Since you're assuming to have enough knowledges about the software, I'll give you some tip about the hardware. The easiest way to exchange data is surely via serial (e.g. RS232): to achieve that, you only need any RS232 shield, or build it by yourself, using a MAX232 chip. Both the Bluetooth and the USB could be a bit harder, but...honestly I don't have much experience on that. Well, you may even consider the "USB" as a very common USB-to-RS232 adapter. In such a case, you fall back into the above case. Bear in mind that you may add even the Ethernet way to exchange data. To drive the door lock, it should be simple. I say "should" because you must know some detail about how to command the electromagnet. That is the voltage, the current, whether DC or AC, etc. This is the very first task to do. Hope it helps. Cheers

[WahidM]

Thanks for your replies/ suggestions guys. The device intended to use would be a rugged mobile device such as a Symbol MC70 or Psion EP10 running Windows Mobile 6.5. I think the serial connection would be more robust and interoperable. Once this connection is established, I could get the software to send a command over serial which gets interpreted and analysed by the Netduino to do the unlock. I think I am more concerned about how to hook up an electromagnetic lock to the Netduino and get it to do the unlocking and monitoring when the user has shut the door. Can you give me some tips on what sort of circuitry I need to buy (i.e. Netduino, electromagnectic lock, serial sheild....)? Thanks

[Mario Vernari]

A serial RS232 shield could be this one, although you may find similar devices anywhere.

About the lock, I cannot help you. I guess that should be a component sold by the doors manufactures, or specialized markets.
However, you may ask of a electric-driven lock, *preferably* using low voltages (i.e. under 24V), and DC.

Tell me more.
Cheers

[Dan Morphis]

I need to then check to see when the door has been closed and a message back to the connected mobile device via the USB, Bluetooth or serial.

There are many ways to see when the door has closed. Does the mag lock your using provide an output which toggles high/low when the door is closed/open? If so, you need to verify the voltage it puts out is within the Netduino's params, but you can easily hook that up to a pin on the Netduino.

Another method is a simple normally open momentary push button. Mount the push-button such that when the door is fully closed (with the mag lock engaged) the button is depressed. Then wire the 3.3v pin from the Netduino to one lead on the switch, and the other lead to a digital I/O pin on the Netduino. Then its a simple matter of setting up the pin as an edge triggered input port in code and acting upon the change.

-dan

[WahidM]

A serial RS232 shield could be this one, although you may find similar devices anywhere.

About the lock, I cannot help you. I guess that should be a component sold by the doors manufactures, or specialized markets.
However, you may ask of a electric-driven lock, *preferably* using low voltages (i.e. under 24V), and DC.

Tell me more.
Cheers

Thanks for the link, I will add the RS232 sheild to my list. I think your right about the electric-driven lock. I need a fail-sucure electric strike which I beleive can come with monitoring. I just need to get this wired into the board.

[WahidM]

There are many ways to see when the door has closed. Does the mag lock your using provide an output which toggles high/low when the door is closed/open? If so, you need to verify the voltage it puts out is within the Netduino's params, but you can easily hook that up to a pin on the Netduino.

Another method is a simple normally open momentary push button. Mount the push-button such that when the door is fully closed (with the mag lock engaged) the button is depressed. Then wire the 3.3v pin from the Netduino to one lead on the switch, and the other lead to a digital I/O pin on the Netduino. Then its a simple matter of setting up the pin as an edge triggered input port in code and acting upon the change.

-dan

Good idea. if i can get hold of a monitored electric release lock then I'm pretty sure that it will do what you have suggested. Failiing that the switch is an option, its pretty much like a fridge light (i.e. when the door is open then the light comes on, when closed it will switch off).

[SupremeArchitect]

I am just starting to mess around again but an easy way to see if the door is closed is to use a magnetic reed switch like the one used in burglar alarms.