Modifications

Here I will demonstrate a simplified design of my own, a parallel resistor system that uses less components and has good accuracy for Arduino-type analog inputs. The complexity grows with the number of sensors, so I will show for three sensors on a branch.  

Here I will demonstrate a simplified design of my own, a parallel resistor system that uses less components and has good accuracy for Arduino-type analog inputs. The complexity grows with the number of sensors, so I will show for three sensors on a branch.  

{{ADFImage|Trinket-Alarme-Base-11.jpg|640px}}

{{ADFImage|Trinket-Alarme-Base-11.jpg|480px}}

Normally the Analog Input A1 is pulled high by resistor R4. If any of the switches S1, S2, or S3 is closed, the resistance changes in a predetermined way. Circuit-wise, each of the resistors R1, R2, and R3 would add to the total resistance using the familiar circuit formula 1/R = 1/R1+1/R2+1/R3. All we have to do is measure the analog values read by the Trinket and add them to our code. This method also works equally well for normally open or normally closed switches.

Normally the Analog Input A1 is pulled high by resistor R4. If any of the switches S1, S2, or S3 is closed, the resistance changes in a predetermined way. Circuit-wise, each of the resistors R1, R2, and R3 would add to the total resistance using the familiar circuit formula 1/R = 1/R1+1/R2+1/R3. All we have to do is measure the analog values read by the Trinket and add them to our code. This method also works equally well for normally open or normally closed switches.

This method does take only four resistors whereas the pure [http://en.wikipedia.org/wiki/Resistor_ladder R-2R ladder method] requires five to six resistors for 3 switches).  

This method does take only four resistors whereas the pure [http://en.wikipedia.org/wiki/Resistor_ladder R-2R ladder method] requires five to six resistors for 3 switches).  

{{ADFImage|Trinket-Alarme-Base-12.png|480px}}

{{ADFImage|Trinket-Alarme-Base-12.png|640px}}

<small> R-2R ladder (source: [http://en.wikipedia.org/wiki/Resistor_ladder Wikipedia])</small>

<small> R-2R ladder (source: [http://en.wikipedia.org/wiki/Resistor_ladder Wikipedia])</small>

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