This application note describes how to use the AD7142 and capacitive sensor ring to achieve a single position digital camera shutter button similar to a traditional 35 mm SLR camera. In addition to making it easier to control the activation of the shutter button, other advantages include faster pre-focus and cheaper shutter buttons. Figure 1 shows the block diagram of a single-position shutter button surrounded by a capacitive sensor ring connected to the AD7142 and HOST μC (microcontroller). The capacitive sensor loop radiates an electric field around the shutter button and, in conjunction with the AD7142, detects in advance that the user's finger is approaching the shutter button, setting the INT pin to alert HOST μC. The HOST controller then begins the necessary processing to complete the pre-focus step before the user actually touches the shutter button. Figure 1. Capacitive sensor shutter button functional block diagram There must be a 1.0 mm exclusion zone between the edge of the capacitive sensor ring and any metal parts (such as camera metal casing, metal shutter button or conductive metal paint). This is to ensure that the capacitive field is not coupled when the user operates the camera. To the metal shell at the virtual ground level causes false detection. Figure 2 shows the metal exclusion zone, where d1 = d2 = 1.0 mm (minimum). Figure 2. Metal restricted area Figure 3 shows a user's finger hovering over the shutter button a certain distance D from the capacitive sensor ring. The sensitivity of the capacitive sensor loop determines when the user's finger can be detected when the user's finger approaches the shutter button. If the sensitivity level is set too high, the autofocus motor will start prematurely, resulting in unnecessary power consumption. To avoid this, set the sensitivity to a lower level, requiring the user to partially touch the shutter button and the AD7142 to assert the interrupt output. Figure 3. Finger in the "D" position above the shutter button 2.0 Rgb Computer Speakers,Rgb Light 2.0 Channel Speaker,Knob Control Function 2.0 Speaker,Rgb Without Bluetooth Speaker Comcn Electronics Limited , https://www.comencnspeaker.com
