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Hi..I'm new to the forum and have been in electronics and communications for many years but have not kept up with the latest in logic circuitry.

I want to monitor, real-time, the opening and close of any door or window in a large metal building, twelve total, from an adjacent nearby office in another building. I have installed a 24 wire underground cable between the two buildings. With the use of a 5V supply and magnets and reed switches on each window/door I plan to input these through the cable to four, quad NAND gate chips. These four outputs would input a single quad AND gate whose output would change state on any window/door opening and an alarm would sound. In addition, the inputs to the four, quad NAND gates would also go to four, quad JK flip flop latches. These 16 latch outputs would each drive a 20 ma. LED. These LED's would indicate a window/door had opened but remain lit when closed due to the latch. A common reset would reset all latches. I'm not finding a flip flop that will handle a 20 ma output to drive a LED. I may need LED drivers. Any comments or ideas on this? Thanks.

Hi FF-Dave

I assume, that you use the 74xx-family, because I've seen that you're using a 5 Volt supply.
I think that a transistor is the best solution. If you use it in GES-configuration, that is:
You can use every NPN-transistor

1. you have to connect the base,(with a resistor) to the output of your flipflops. (base resistor)
2. you have to connect the emittor to ground. GES-configuration = CES: Common Emittor ??)
3. you have to connect the diode to 5 Volt, in series with a resistor (collector resistor)
4. you have to conect this resistor with the collector
5. if you know the amplification factor of the transistor
and the max. current that the output can (and may) provide, you can start calculating

Calculation
The visibility of most LED's is good, when the current is about 15 mA.
So the collector resistor, you can use is 5/15 kOhm. Thus a resistor of 330 Ohm will do.
You can calculate the value of the base resistor by mutliplying the the value of the collector resistor and the amplification factor.
Suppose that the amplification factor is 200, then the base resistor can be 200 x 330 = 66000 = 66 kOhm
An existing value nearby is 68 kOhm.
The output current of the FF is then 5/68 = 0,07 mA.

Well FF-Dave, I hope you'll understand my explanation.
I'm sorry, when my use of the English language is not quite correct.

best regards
Hans Cadans
The Netherlands

Thanks for the info. I was hoping to use the 74xxx flip flop to drive the Led's instead of adding a transistor driver to do it. Also it would be nice to have a multiplex scheme where all inputs could be inserted into a serial wave train then demuxed at the remote location to display on a panel. Anybody done this?

Hello FF-Dave,

I, for myself, would just suggest this solution before.
But I thought, you had already made, built, the circuits.

Instead of a multiplexed system, I would propose a system with registers.
As input, you can take a Serial/Parallel-IN to Serial OUT register.
Take care of the inputs, for these you need to use normally closed contacts.
The alarm is given when a contact is opened. You will have to tie up your reed-switch to power (incl a resistor)
Keep the current through the switch as low as possible.

For monitoring the inputs, you need a Serial-IN to Parallel-OUT register.
You can see constantly the changes of the inputs, at the outputs of register CD4094
If there has been an alarm-situation,you see, which contacts have been activated after the attached JK-Flip-Flops.
The LED's can be placed on a plan of the building, nearby the doors and windows.

Between the input-circuitry and the monitoring-circuitry, you need four wires
clock
data
read
ground

If the input-circuitry hasn't a power-supply of it's own, you need another wire.

For the clarity I will attach a design in Logic Circuits.

Best regards
Hans Cadans

Hi Hans..

Your suggestion of using registers of parallel to serial and then back to parallel is exactly what I would like to do. I tried to open your circuit attachment but was unable to. Can you resend with different file type? Thanks for your help.

Dave..

Dave,
You can open this file with the program that is hosted on this forum. Just download and install it:
http://logiccircuit.codeplex.com/releases/
Eugene

Dave,

I've replaced the file by a more sophisticated version.
Let me know, if you succeeded in downloading the file

regards
Hans

Yes, I have downloaded the file. Thanks. I'm having trouble understanding the symbols. I really only need a 15 bit capacity which may simplify the circuit.

My first introduction to logic circuitry was over 50 years ago when I was employed by Lockheed Martin. at Cape Canaveral, Florida. There I worked as an electronic technician on the Research and Development of the Titan missile weapon system. My area was in Telemetry, which is a radio system between the missile after it lifts off and the ground station to record all necessary parameters of missile performance while in flight. The Titan missile was the first to utilize a new concept of digital modulation called PCM. (Pulse Code Modulation) which today is just called digital. Earlier Telemetry systems used analog FM/FM modulation. In 1965 I joined Boeing Aerospace and worked on the Appolo Moon Landing mission in the same field of Telemetry. I'm proud to say, I was one of over a 100 people in the Firing Room of several launches when the Astronaut's were sent to the moon. All of these accomplishments were done before the personal or desktop computers were born. In fact Calculators were just born then. Every Engineer and Technician used slide rules. Well, I've said enough.

Dave..

Dave,

I managed in making the same circuit in nearly real IC's (pin layout is correct). It took me a few evenings (nights) to accomplish this.
I upload the new file right away. I worked on the whole thing since last sunday.
It's nice to know something about you. I've figured out that we must have about the same age.

I'll write you something about myself by the private mail, within this forum.
Please let me know, if the system represents that what you wanted.

When you want more real IC's, you'll have to wait a little while, because I'm workin' on that too.
I've already seen some interpretations, but with most of them, the internal Flip-Flops aren't correct
The problem in here is that I have to translate all the comments in English.
At (In?) any case, my English has approved, since I joined this forum (not long ago, just before you did)

With no doubt I will forget something to explain, but you can ask me anytime, if anything is not clear to you
Hans Cadans

Hans.. I sent you a PM.

Dave..