Call or Signal Box for Warehouse

[foxtrot]

I've been tasked with figuring out how to make a call box for our warehouse at work. We have a will call for people to pick up products, but the employee responsible for handling those things (me) is usually elsewhere in the facility.

We want our customer to walk into the will call area and press a button which will momentarily ring a bell (or multiple in various locations) and turn on a/multiple lights. The bell should ring only as long as the button is pressed, but the light should remain illuminated until a second button is pressed by me when I arrive to the customer.

So, how does one build a simple system which has one button to momentarily ring a bell and activate a light, and a second button to deactivate the light?

I know the basics. I could wire in just the bell portion and one button like a doorbell, I could also set up a button to momentarily illuminate a light via relay. Don't know how to combine the two into one and keep the light sustained until canceled (without the customer having to HOLD the button).

 

[73's de Edd]

Pull out yore doorbell , lite "bub", battery(ies) and a 'tousand feets of "war" . . . . .




73's de Edd

 

[AnalogKid]

The nice thing about this circuit is that it can run on anything. As long as the light, bell, relay coil, and relay contacts all are rated for the same operating voltage, it can be 5Vdc, 240 Vac, or whatever.

IF the DPST customer switch is a problem
AND IF the circuit is running on a DC voltage source
THEN the customer switch can be SPST with the addition of one diode.

ak

 

[kellys_eye]

Get a wireless doorbell - many, many versions available these days. Simple matter to fix a manually resettable external alarm to it (locking relay or resettable monostable etc).

 

[AnalogKid]

What are the power sources for the alarms, lights, and control circuit?

ak

 

[foxtrot]

Get a wireless doorbell - many, many versions available these days. Simple matter to fix a manually resettable external alarm to it (locking relay or resettable monostable etc).

I say this in a friendly manner and as someone who doesn't consider himself patriotic, but that lacks the American spirit of know-how and getting stuff done. Personally, I'd just rather go the full-custom route. At that being said...

What are the power sources for the alarms, lights, and control circuit?

ak

I plan on aquiring a AC-DC power supply to provide low voltage (<50V) to power the system. Will probably go for 24V, 30V or 40V as most of the lights I would want to use for the system are one of those voltages. Haven't looked into buzzer or bell voltages, but that's an easier thing that can be dealt with later. One other consideration here is code: I can't have a customer touching a device I made that has line voltage in it. I plan to do things anally well, but regardless don't want any risk.

...IF the DPST customer switch is a problem
AND IF the circuit is running on a DC voltage source
THEN the customer switch can be SPST with the addition of one diode.

ak

The only reason why a DPST would be a problem (that I'm aware) is getting/having one. Is there any other concern?

Otherwise...

Pull out yore doorbell , lite "bub", battery(ies) and a 'tousand feets of "war" . . . . .

View attachment 34855


73's de Edd

I can't believe I didn't think through it and come up with that before. You just have to find a way to keep power going to the relay after it's been activated--duh--hook it to itself. Well then it's stuck on--so kill the power to everything. Brilliant!

Thank you!

 

[AnalogKid]

Not only is a relay latching itself is older than Ed, it's even older than me. The classics never go out of style.

UL 1950, now EN60950, has rules about safe voltages, called SELV (Safe Extra Low Voltage). It is something like 32 Vac and 42 Vdc. Ish. I recommend 24 Vdc for the entire system. It is common in industrial control and alarm systems, so there are tons of relays, lights, sirens, beepers, bells, etc. to choose from.

ak

 

[ChosunOne]

Not only is a relay latching itself is older than Ed, it's even older than me. The classics never go out of style.

UL 1950, now EN60950, has rules about safe voltages, called SELV (Safe Extra Low Voltage). It is something like 32 Vac and 42 Vdc. Ish. I recommend 24 Vdc for the entire system. It is common in industrial control and alarm systems, so there are tons of relays, lights, sirens, beepers, bells, etc. to choose from.

ak

Just to be precise, it's common in industrial Fire (and possibly environmental) alarm systems. Security alarm systems virtually all run on 12 VDC these days.

 

[AnalogKid]

Works for me.

ak

 

[foxtrot]

I've been wondering about voltage drop. The longest run of wire between the control box and the lights/buzzers will be around 200-300ft (closer to the 200 end of the range).

Looking into buzzers and lamps, I can expect to need up to 0.5 amps to power probably two buzzers and two lights.

How much voltage drop can I accept? Basically I just need to determine what gauge of wire to run. 18/3 would give me a rounded 2V of drop over 250 feet--will this cause an issue with two bells and two lights hooked up to the system in parallel? What about 22/3 with a drop of 4V?

 

[foxtrot]

I may have a fundamental misunderstanding regarding voltage drop. I need about 0.5 amps to power all the devices, but is that the number I should use in calculating voltage drop, or should it be dependent on my power supply?

I really feel like I should just experiment to figure it out instead of relying on 'hand-outs' here, but this is a matter of company time and expense. Boss probably wouldn't be thrilled to buy me a few spools of different gauge wire.

 

[ChosunOne]

I'm an alarm technician with decades of experience. I have run many many siren/bell cables over distances of 200-300 feet that carried more than 0.5A and never had a problem. Some sounder/strobe circuits have to carry several times that load. The resistance/voltage drop in 18 AWG wire is negligible at that distance compared to the resistance of your buzzers & lamps. 18 AWG wire gives you a very comfortable margin.

 

[AnalogKid]

I may have a fundamental misunderstanding regarding voltage drop. I need about 0.5 amps to power all the devices, but is that the number I should use in calculating voltage drop, or should it be dependent on my power supply?

Voltage drop calculations are based on the supply *voltage* and the load device *current*.

1. Add up all of the load currents, and get a supply with at least 50% more output current than that. Example - for a 3 A total load, a 4 A supply is too little margin, but a 5 A supply should run forever.

2. With a wire resistance table and Ohm's Law, you can calculate the voltage drop for any load. With the load device (bell, light, whatever) datasheet, you can determine the minimum acceptable working voltage. Increase the wire size until the drop at that current and that distance leaves enough voltage for that device.

ak