B&B Electronics Asynchronous to Synchronous Converter 2010 Manuale Utente Scaricare il pdf (Pagina 16)

Department of Computer Science and Electronics

2.6. Previous design

The old system tests the field and it also gives back whether there is a white line

under the robot or not. The system is composed by tree equal cards. The schematic

corresponding to a single card is exposed in appendix D.

When there is a change of playing field, it is necessary for the cards to be

calibrated manually using a potentiometer.

Since there are eight sensors that they will have a single manual calibration

system, it may be impossible to set the optimal value for all sensors.

The sensors tolerance will depend on the signal called level. In addition, point 1

of the schematic (figure 2-12) illustrates how this signal is set. Making this calibration

will take some time and it doesn’t guarantee any precision because human error will be

implied among other things.

The mentioned manual calibration system is designed with a variable resistance,

a transistor and a passive filter so far. Using the variable resistance the transistor base

current can be modified. At the same time this current fixes the collector and emitter

current. This emitter current is transformed into a voltage by the filter stabilizing the

level signal.

The transistor in the second point of the schematic is working like a switch

whose state depends on the gate voltage that is set by the signal called load. Therefore

when the switch is ON, the level signal flows from the drain to the source pin generating

a current in the bases of the transistors located in point 3 of the schematic.

Consequently, the current is going through the sensors’ infrared emitting diodes taking

eight samples, one for each sensor.

Figure 2-12. Point 1 in the schematic

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 42 43

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B&B Electronics Asynchronous to Synchronous Converter 2010 Manuale Utente Pagina 16