The 1129 is actually a capacitive change sensor. When the capacitance changes the Sensor Value reports 1. If the Sensor Value remains at 1 for longer than 60 seconds, it will recalibrate back down to 0, regardless if the sensor is still being touched. This recalibration can also be done manually by unplugging and plugging the sensor back into the HUB0000 (or compatible product). This is a useful feature because it means that the sensor can be mounted on a flat surface such as a piece of glass or plastic and be reset so that it does not register the change in capacitance caused by the surface it is mounted on. On the bottom side of the 1129 there is a small exposed metallic pad. A soldered connection can be made to the pad to increase the size and dimensions of the touchable area, such as attaching the sensor to a metallic object or some wire. Once the sensor is recalibrated, the Sensor Value will increase to 1 if the attached object is touched anywhere. Although there is an exposed metallic pad on the bottom of the board, the pad does not have to be touched directly to activate the sensor - touching anywhere on the board will activate the sensor. The 1129 can work as a close proximity sensor, sensing objects at a distance of up to 1/2" from the board in all directions without direct contact. The 1129 will also work through a thickness of up to 1/2" of glass, plastic, or paper.

Phidget Cable

The Phidget Cable is a 3-pin, 0.100 inch pitch locking connector. Pictured here is a plug with the connections labelled. The connectors are commonly available - refer to the Analog Input Primer for manufacturer part numbers.

The capacitor labelled C1 is the sensing capacitor. In other words this is the capacitor that determines how sensitive the sensor is. By default it is a 10nF capacitor. By changing this value we can adjust the sensitivity. Smaller capacitors will yield lower sensitivity while higher values will yield higher sensitivity. The integrated circuit (IC) on the 1129 specifies that the acceptable range for C1 is 2nF-50nF. In testing, 2nF will not sense through any thickness of material while 50nF can sense through over 1" of material and even through double paned windows with an air gap of up to 3/4". If the size of your capacitive touch surface is very large, you may have to increase C1 even more. Up to 100nF even. (C1 is soldered onto the board, in order to replace it you will need a soldering iron).

The DST1200 will fire saturation error events when the nearest reflection is closer than 40mm from the sensor. At this range it is too close for the sensor to accurately determine the range of the object.

If this happens, it could be due to interference on the power supply. If you're using the 1129 on a Wireless VINT Hub, laptop, or PhidgetSBC, try switching out the power supply to see if the problem persists.