Alarm Logic - Is there a simpler way to do this?

[Rob]

I’ve just installed an NFC code touch to simplify arming and disarming our intruder alarm rather than having to use the app.

However, the inputs on the burglar alarm block mean that I cannot use a single code to arm it with delay when we leave and disarm it when we return as this requires pulses on 2 inputs (Ad) and (Off) respectively. There is a toggle input (Tg) but this only arms/disarms the alarm, there’s no parameter or option for it to arm with delay.

To get round this I have created some quite convoluted logic, see pic.

By way of some explanation, as the status output of the burglar alarm block also includes a 2 status if the presence sensors are not used a Status block is needed to provide a simple 0/1 output to denote armed/disarmed. The radio button block takes the NFC code output and triggers either the Arm/Disarm input on the burglar alarm block. This block also takes inputs from the Status block which ensures that however the alarm is armed/disarmed (by logic, leaving house mode, app etc) entering a code on the NFC touch will change the state correctly.

Whilst this logic works very well, and is invisible to users, I just feel like I’m missing a trick and there is a more elegant logic solution for this.

Any thoughts?

[Jonathan Dixon]

I may have misunderstood / oversimplified, but isn't this just a case of gating the NFC pulse so it only turns the alarm on if it's currently off, or else off if it's currently on? i.e. a pair of AND should do it:

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[Rob]

Yes, that's what my first thought was, but when I used a couple of AND blocks in that way the alarm would turn off and then imediately start to re-arm. Strange!

[Jonathan Dixon]

On Tue, 28 Feb 2023 at 10:31, Rob <robertl...@gmail.com> wrote:

Yes, that's what my first thought was, but when I used a couple of AND blocks in that way the alarm would turn off and then imediately start to re-arm. Strange!

Ah yes I can see how this would happen, it's racy: if the NFC output pulse is long enough (or really anything longer than one cycle i,e, 20ms) then S will go high on arm so sneak through the other AND gate, immediately trigger a new rising edge on the Off input, before the NFC pulse has finished.

The logic you have is probably as simple as it gets then, as you need something to correctly marshal out strictly one on or off pulse per NFC press.

Stylistically I'd probably use a Switch block, as it has the edge detection already built in, but no real difference 

 

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