5504GI (analogue input) with resistor ladder switches

Hi,

I'm planning on a reasonable large new (residential) installation and am looking at ways to minimise cost without sacrificing functionality. Looking at my budget estimates there is significant cost for inputs (switches and PIR's).

In electronics it is not unusual to apply a resistor ladder/network in order to use multiple switches on a single analogue input. I was looking at using a 5504GI which has 4 channels and 8 tresholds per channel. From what I gather this would allow me to use potentially 4 x 8 = 32 inputs on a 5504GI single box. This would allow me to use low cost bell press switches in combination with cheap PIR's. These would all be used to switch lights.

I understand that the purist or those without budget constraints will argue against this solution but would like to understand if anybody else has experience with this or why it wouldn't work.

Thanks,
DO

 

You might be able to make some things work, but it will be very limited and unlikely to satisfy the customer.

The first problem you will have is that you will only be able to detect one button at a time, so you have to use a bell press operation. You obviously can't control the lights with a bell press, so you then need to get this to control (probably toggle) the state of the load. This could be done with some logic code, but it it going to be tricky, and not particularly responsive.

You then need to deal with dimming somehow.

You would also have no state feedback (LEDs).

The end result would be a very non-standard system which will be difficult to maintain and impossible to extend.

If your customer is on a tight budget, the best idea is to put in the bare minimum of infrastructure to start with, then add the nicer features later.

 

If you are planning to connect "cheap" PIR's to the General Input Unit using this method then I think you will really struggle to get the flexibility you'll need to make this really work for you. You'll be able to detect that a contact is closed or open... but that's all. You will lose a lot of functionality using this approach.

An option that is not that much more expensive would be to use the Auxiliary Input units. This will give you all the standard key functions (unlike the General Input Unit), allowing you to do things like timers and dimming, and allows you to have very long cables connecting your dry-contact switches or relay outputs to the unit.