New photo-interrupter series now available

Opto-Electronics

7 March 2007 Opto-Electronics

The AEDS-9310 and AEDS-9300, are the first series of photo-interrupters released by Avago Technologies. Using transmissive technology, the AEDS-9310 has a standard 5 mm gap slot with vertical mounting leads while the AEDS-9300 has a 2,7 mm gap slot with horizontal mounting.

These non-contact interrupters are robust and according to the manufacturer, their mechanical dimensions and electrical characteristics ensure they are a direct drop-in replacement for many compatible photo-interrupters in the market today.

This transmissive subminiature photo-interrupter consists of a Gallium Arsenide infrared light emitting diode and an NPN silicon photo-transistor built in a black plastic housing. It could be mounted onto a PCB with a current-limiting resistor in series externally with the infrared LED. With this, the input voltage for the LED could share the same voltage level as Vcc. Regarding the photo-interrupter output, there will always be current output measured but with the external resistor, RL connected as shown in Figure 1, analog voltage outputs can be obtained.

Figure 1. Basic configuration of the photo-interrupter

With both the infrared light source and the photo-transistor in a single package, the photo-interrupter employs transmissive technology to sense an obstacle's existence, act as an on/off switcher, or even to sense low resolution rotary or linear motion. The photo-interrupter is specified for operation over -25 to 85°C temperature range.

As a basic switcher, the photo-interrupter would have position detecting characteristics as shown in Figure 2. These characteristic diagrams give the relationship between relative light current, IL and distance of displacement, d. Note that for the slot, the obstacle could be introduced between the emitting diode and the photo-transistor in two directions; one is in the X-axis and the other in the Y-axis.

Figure 2. Photo-interrupter positioning sensing characteristics. Obstacles may interrupt along X- or Y-axis

Therefore, with the obstacle's presence in the slot, the photo-interrupter would give a low logic output. And vice versa, it will provide a high logic output without the obstacle (see Figure 3). Typically, Rise Time, tr and Fall Time, tf will have the same value - 20 ms. With special design of the object passing through the slot, periodic presence and absence could be generated. Such an output signal is useful in determining low-resolution (>0,5 mm pitch) motor rotation positioning and motor spinning speed.

Figure 3. Response time measurement of output signal

Figure 4. Periodical output signal could be used to determine the motor spinning speed and rotation positioning

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New photo-interrupter series now available

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