Laser Detection: Handling Multiple Detector Circuits
Posted on Wednesday, 12 December 2012
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In the post Laser Detection it was discussed how to set up a detector
circuit and how the Arduino would recognise when the LaserBot was hit through
the use of an interrupt. That was only for one detector circuit. However, three
detector circuits are wanted on the LaserBot to make the game more interesting
– more targets to shoot at, different points for the different targets etc.
Therefore, it was decided to use the two
interrupts available on the Arduino. Two detector circuits would be connected
to one interrupt, and the other circuit would be connected to the other
interrupt. This meant that the Arduino could differentiate between two
circuits, but not three. So, the user could get two different scores for
hitting targets, rather than three different scores, which is not a big loss in
terms of flexibility for the game.
All three
detector circuits were set up as above. Then, the output of the collector of
the transistor for two of the circuits were joined together. This was then
connected to one of the interrupts. The output of the collector of the other
circuit went directly to the other interrupt on the Arduino.
PROBLEM ENCOUNTERED WITH ONE INTERRUPT
At first, only one interrupt was going to be used for all
three detector circuits. This caused a problem in detecting which target had
been hit as the interrupt only notifies the Arduino that it has been hit
but not which target has been hit. The idea was then to have an output
coming off each circuit which would then have its own individual port on the
Arduino. When the interrupt said that the Arduino had been hit, the Arduino
could then check the three different ports and see which ports state had
changed. This, however, did not work as the interrupt joined all three circuits
together, causing all three circuits to change state when they were hit.
HANDLING MULTIPLE INTERRUPTS
Referring to the previous post, the second interrupt is
set up in the exact same way as the first interrupt. The interrupts are on pins
2 and 3 on the Arduino Uno. To enable the second interrupt, the following line
of code needs to be added where the first interrupt is enabled.
EIMSK |= (1 << INT1); //Enable external interrupt INT1Then, another interrupt service routine (ISR) needs to be included.
ISR(INT1_vect)
{
unsigned long hitMillis = millis();
if ((hitMillis - lastBlinkTime) > interval)
{
lastBlinkTime = hitMillis;
score = score + scoreRight;
Serial.println("Hit Interrupt 2");
Serial.println(score);
}
}
Both interrupts on the Arduino are now set up and ready to be used.CIRCUIT CHANGE
The other
two detector circuits should be built in the same way as the previous circuit.
However, there has been a change in that there is no longer an LED in the
circuit, as it was no longer needed for the LaserBot. The updated circuit for a
detector circuit can be seen below.
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| Updated detection circuit |
TESTING MULTIPLE INTERRUPTS
To test the
circuit, power was connected to the Arduino and a Serial monitor was opened. Each
of the circuits LDR was hit with a laser. On the Serial monitor, for the two
circuits that are connected together, “Hit Interrupt 1” was printed while for
the circuit that is by itself, “Hit Interrupt 2” was printed. This successfully
shows that two different interrupts are being used.
