User Adaptor

The Smart Sense User Adaptor allows easy connections to in the Analogue Sensor inputs to be made. The adaptor brings the connections from the Smart Box to the sockets on the top of the box. Connection to the adaptor should be made using standard 4mm plugs. When the adaptor is connected to Smart Box the appropriate input will be labelled 'Adaptor'.

The Yellow ‘input’ socket on the adaptor accepts a voltage between 0 and 2.5 volts. As the voltage on this socket rises the reading from the adaptor will rise linearly from 0 to a maximum reading of 255. The adaptor also includes a 0 Volt (black) and +5 Volt (Red) socket to provide power to an external circuit. The external circuit can draw up to 50 mA from the adaptor. The V ref. (White) socket provides a stable 2.5 Volt source (max. 20mA) which can be used as a reference voltage.

The following example circuits show some of the possible uses of the adaptor.

Simple light sensor

Fig. 1

The circuit shown in fig.1 uses a light dependent resistor (L.D.R.) to form a light sensor. The L.D.R. and the 220Ω resistor form a potential divider. The resistance of the L.D.R. increases as the light falling on it decreases. In very dark conditions the resistance will be at least 1MΩ so only a small voltage will be present at the input socket. In bright conditions the L.D.R. will have a resistance similar to the 220Ω fixed resistor and so the input socket will see a voltage of around 2.5 volts which will give a maximum sensor reading of 255. Typical uses of this type of sensor include:

• Measuring daylight during the day to determine if it has been ‘sunny’ or ‘overcast’
• Detecting dusk and switching on a security lighting system.
• Measuring the amount of light which passes through a variety of materials.

Detecting rotation

Fig. 2

The circuit shown in fig. 2 uses a linear potentiometer to detect rotation. The track of the potentiometer is connected between the Vref. and 0 Volt sockets. The input socket is connected to the wiper and as the spindle is rotated the potential divider formed by the two sections of track produces a voltage which swings between around 0 volts up to the maximum of 2.5 volts. Typical uses of this type of sensor include:

• Detecting when a lifting bridge has reached the open position.
• Measuring the angle through which a pendulum swings.
• Sensing a water level by attaching a buoyant lever to the potentiometer.

Reflective opto switch

Fig. 3

Figure 3 shows how a reflective opto switch can be connected to the adaptor. The device contains an infrared transmitter and receiver. The infrared beam is directed outwards and when a reflective surface is placed near the end of the device a change in voltage will occur on the line connected to the input socket. When the detector receives only a small amount of reflected light the voltage produced will be low and will rise as the detector picks up more infrared light. Typical uses of this type of sensor include:

• Sensing the ‘colour’ of various objects by measuring the amount of infrared light they reflect.
• Measuring short distances as a reflective surface moves within the sensor’s range.
• Reading ‘bar codes’ by detecting if the sensor is over a black (non-reflecting) surface or white (reflecting) surface.

The adaptor also allows the reflective opto switch to be used as a digital sensor. Unplug the lead from the ‘input’ socket on the adaptor, and plug it into the yellow socket of one of the digital sensor inputs on the Smart Box. The leads plugged into the ‘0V’ and ‘5V’ sockets on the adaptor remain connected.