WahidM

... and try the same thing at the Netduino. Disconnect the RS232 break out board, and then connect D0 to D1.
That will allow you to verify the Netduino's serial code.

Sorry for the late reply on this.

I swapped over the PINS and it seems the netduino isnt receiving any data, although the TX light flashes on the serial shield to indicate activity. Could this be something to do with my Netduino?

Thanks for your response guys. The RX light flashes when sending data from Netduino to PC however the TX light doesnt flash when sending from PC. I have also checked the flow control and its set to none (using Tera Term software aswell). I created a test app on the PC side to see when the data gets sent but still nothing happens at the netduino side. I even tried it on another Netduino board! It does look like the data is getting out of my PC as the Tx light isnt flashing, but not sure what other settings I could change PC side. Is there a way of using different Pins to represent a different COM port on the netduino to see if thats an issue?

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).

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.

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