Providing custom solutions to your clients is an important differentiator for many locksmiths. There are endless sources for off-the -shelf products from on line sources, retailers and service providers; but fewer sources for customized solutions.
I learned a few things along the way where custom systems are concerned. Most importantly, listen to your client, but remember that you are the expert, and whatever you do it has to meet code.
I recall customers who would request I install equipment which they hoped would reduce shoplifting but which unfortunately would violate building codes so I refused.
The best tool for the locksmith is product knowledge and knowing where to get technical support when they need it. Many products have capabilities which may not be apparent without looking closely. Also products can be interfaced with other products to achieve different functions.
This month’s project involves providing the customers the means to monitor doors in their facility with large LED displays. When the door is closed, the green LED is lit, and when the door is open, the green LED goes out and the red LED illuminates.
You can do this a per-door basis and provide multiple displays for numerous openings. This set-up is helpful if there are exterior doors which are concealed from view, such as in stairwells or cannot be easily viewed.
This ‘simple’ circuit can be expanded and enhanced depending on your requirements. It does not involve controlling doors and does not affect life safety.
Let me explain the function of the circuit and each of the components.
First you’ll need a 24 VDC power supply. The components in this circuit all require direct current (DC), rather than alternating current (AC). Alternating current is what comes out of line voltage receptacles. You lower the 120 Volt ‘line voltage’ to a more convenient level (in this instance, 24 Volts), with a transformer. Then the AC must be rectified & filtered.
Power supplies are a topic all their own, and we will not cover them in this article. Originally this circuit used a power supply which was powering the lock and keypad on the door.
For this project, you can use a plug-in DC power supply rated for 24 VDC@1 Amp. To figure out what size power supply is required you must add up the total current required by all the components in the circuit. A plug-in is more convenient than a power supply which must be connected to line voltage by an electrician. In the real world, you must install your equipment and wiring so it is protected from damage. Plug-in power supplies are available with wire leads or screw terminals. Some wiring will be required, and you can use #18 or #22 gauge stranded.
The LEDs are ½” diameter and can be operated at either 12VDC or 24VDC.
I like them because they are visible in normal lighting over a great distance, so guards or nurses can tell easily whether the door is open or closed. They need to be physically mounted.
The LEDs are connected to a relay. The relay is controlled by a closed circuit door sensor. In access control, this sensor is often referred to as a DPS (Door Position Sensor) on diagrams. These types of sensors are typically used on alarm systems, and door sensors are available in many sizes and configurations. The one in this project is the model 4460 miniature aluminum commercial surface mounted switch set manufactured by George Risk Industries (GRI). George Risk has many types of contacts and other products.
There are also larger aluminum sensors, which you typically see on overhead doors, but for swinging doors, I think they are over the top. Clients ask “what the heck is that thing?”
In security systems, the trend is to hide sensors, and frequently they are concealed from view. This sensor is surface mounted, has an aluminum casing and aluminum magnet, and its leads are protected in an armored cable. This simplifies installation since the cable can also be surface mounted rather than having to conceal it. The cable has to be firmly mounted so it does not flop around or invite tampering.
The installation environment determines how you install the contact and cable. For an institutional environment, the visibility of the robust surface mounted contact is a reassurance to some and a deterrent to others. This switch can be specified with different contact configurations. This one is closed circuit when the door is closed, open circuit when the door is open. The switch contacts are rated for around 500mA (about a half an amp). I use the relay so I know the DPS will never be required to operate a load larger than the relay’s rated coil current. I also use the relay to electrically isolate the components in the circuit. It is easier and cheaper to replace a relay then a DPS.
The relay being used is an Altronix RB1224. Again, a large variety of relays are available for low voltage applications. This one has two sets of form “C” contacts referred to as Double Pole Double Throw (DPDT) which change state (switch) when voltage is applied to the relay coil. The coil operates at 12 or 24 Volts (switchable) and draws 75 mA. This relay also has its own red LED that illuminates when voltage is applied to the coil. I find this feature helpful when troubleshooting circuits.
Components are:
- 1 pc. Power Supply
- 2 pcs. Red LEDs (Alarm Controls #LDR-L)
- 2 pcs. Green LEDs (Alarm Controls #LDG-L)
- 1 pc. Relay (Altronix #RB1224)
- 1 pc. Closed Circuit Magnetic Door Sensor (GRI #4460)
This circuit can be enhanced an interfaced into many variations.
