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#9070 - 02/09/03 02:33 PM SECU Input Voltage Divider Tool
John Warner Offline
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Registered: 01/09/03
Posts: 817
Loc: Port Perry, Ontario, Canada
The attached spreadsheet (in 123 and XLS formats) provides a quick and easy way to select resistor values for a voltage divider for SECU inputs. With this voltage divider and two switches, you can use a single SECU input to sense all combinations of states of the two switches.

The spread sheet will then calculate the analog values the SECU will see for each state.

While initially conceived to monitor the status of a garage door using magnetic switches, it can be used for any number of similar applications. By putting one switch on each of two garage doors, a single SECU input can monitor both.

Since the SECU-16 and -16I differ in analog values, both are included in the sheet.

Many thanks to Guy Lavoie for figuring out how to do this and for his valuable input on the spread sheet!

(attachments to be added by ADI)
www.appdigsupport.com/ADI_Files/SECUINCALCRev1.123
www.appdigsupport.com/ADI_Files/SECUINCALCRev1.XLS
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#9071 - 02/10/03 04:40 PM Re: SECU Input Voltage Divider Tool
John Warner Offline
old hand
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Registered: 01/09/03
Posts: 817
Loc: Port Perry, Ontario, Canada
The attachments have now been added.

Thanks Dan!
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#9072 - 02/13/03 09:02 AM Re: SECU Input Voltage Divider Tool
chando Offline
newbie


Registered: 01/11/03
Posts: 1
Loc: Laval, Qc, Canada
John,
I'm working on series of 4 + 1 resistors to supervise 4 contacts. I've done too many hand calulations. I tried to transport my calculations in Excel, but yours looks much better.
Have you considered scenarios using 5 resistors to watch 4 contacts? I'd be interested to see the results and compare with mine. So far, the theory doesn't match the reality.

chando (another canucks!)
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#9073 - 02/18/03 09:04 AM Re: SECU Input Voltage Divider Tool
John Warner Offline
old hand
*****

Registered: 01/09/03
Posts: 817
Loc: Port Perry, Ontario, Canada
Chando

I haven't looked at other VD arrangements. Guy Lavoie dreamed up this approach and is the expert. All I did was put together a spread sheet to pick resistors.

Adding a couple more switches and resistors seems straight forward enough though (as long as you can get enough spread for the various combinations for reliable results). Please feel free to modify the spread sheet any way you want AND to post the results!

Since I got my second SECU, my motivation for this diminished - right now, 24 inputs seems like lots - but that may change!
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#9074 - 02/19/03 04:39 AM Re: SECU Input Voltage Divider Tool
Brian Raynor Offline
addict
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Registered: 01/09/03
Posts: 454
Loc: Columbia, SC
Keep in mind that with the more resistors you use, the more the tolerance of them comes into effect.

With more then 4, you'll probably want to use 5% or better resistors (which are easy to find).
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#9075 - 02/19/03 05:14 AM Re: SECU Input Voltage Divider Tool
Guy Lavoie Administrator Offline
Beyond All Hope
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Registered: 12/21/02
Posts: 6401
Loc: Montreal, QC, Canada
As John mentioned in his last post, getting a reasonable spread becomes harder as you add resistors. The precision also becomes more important (as Brian mentioned) since the errors add up. This is because you'll want to use resistors that are either half of the lowest one or double of the highest to make sure that no two resistors can add up to the value of a third when the switches short them out. The permanent series resistor that that just checks for a complete short doesn't count in this double or half scheme because it's not part of the switching combinations.
_________________________
"If you don't know what you're doing, do it neatly..."

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