Control door with RS232 or Ethernet relay

Question

Our company use a fail safe electric bolt with a remote control for the entry door. It closes when the power is ON and vice versa.

It does work normally but I want to make a hot button for the receptionist to open/close it using her keyboard.

I'm a newbie in electrical and after spending a half day for googling I have found 2 way that I feel it may work:

1. Connect the receptionist's PC directly with the door controller through computer port (USB/Serial).
2. Use an ethernet relay.

Honestly, I have searched a lot but still found nothing fit my need. I want to solder the circuit myself so buying a complete controller is not in the category.

Btw, I intend to make the application using .NET framework (C#).

Any help would be appreciated!

P/S: Sorry for my English if you do not understand.

Answer 1

One cheap and wire-clutter free way to do it would be to use ESP8266 modules. They come in many flavors and ESP-07 is my favorite. This will allow you to control the door wirelessly over a wi-fi network.

There is a project which allows you to program ESP modules using Arduino IDE. This will get you up and running quickly. You will need the wiring diagram given on this page.

If you choose to use ESP-07, then you can safely use GPIO - 4, 5, 12, 13, 14 and 16. There are a few more but you need to be careful while using them. For your purpose six pins seem to be more than enough.

Once the ESP module is ready, you need to select a suitable relay. Better idea is to select a 5V coil relay (i'll explain why). Don't forget the freewheeling diode.

Powering everything up:

1) ESP requires 3.3 V for operation. If you have used 5V relay, then get a 5V adapter and use a cheap 3.3V linear regulator (1117-3v3 for example). If your relay used higher voltage such as 12V, the linear regulator would have gotten quite hot.

2) Relay can be powered directly using the 5V that is coming from the adapter.

Controlling the lock:

ESP can connect to your office wifi as a client. You can write a PHP application and send the signals to ESP using your web browser to control the lock.

Answer 2

I believe it would not be easy with ethernet way if you have no much experience with suitable components.

As about RS232 - see, here is a TXD line and GND line. If you just want to send some signal, you can send anything - bytes like 0x55 or 0x00 will anyway produce some recognizable pattern on a line.

Just read a bit about RS232 port to get idea what voltage levels there are. I believe you can interface them with a diode or two and pull-up resistor. Then you'll need a kind of one-shot timer which, when detect the signal on the line, will generate long enough control impulse to open your door - browse the manual for 555 timer, probably. Use optocoupler or mechanic relay to control the power-line of the door latch if necessary.

The only trick is to make the RS232 working with no more wires. I believe you need to short-circuit 1-4-6 pins between themselves and also 7-8 pins. Check internet for "RS232 3-wire" schematics for more details. Use low baud rate (even 300) to get more detectable signal - you'll be able to see it with led, for example.

If you use USB-to-UART cable of some kind, you need not short-circuit anything and the level interfacing is going to be somewhat simpler as there should be normal logical levels.

Sorry for this is not the most detailed instruction :)