Hello, I am creating a linefollowing robot using the BS2px, utilizing its new COMPARE command. I am using five Fairchild QRD1114 IR sensors, connected together and then to one of the Stamp’s inputs. The other input required for the COMPARE function is connected to a 10k trimpot that acts as a variable voltage divider, to adjust the threshold of when the sensors activate.
The sensors are read by turning on their corresponding LEDs one at a time, and the values are COMPAREd in sequence to the threshold set by the pot.
I am having trouble getting a reading from these sensors, as they will only output a value of 0 (I have tried adjusting the potentiometer, moving the sensors closer to the ground, etc.) and nothing seems to be working. I am wondering if anyone else has experience using the BS2px, or the COMPARE command?
One thing I should mention, is that my Stamp appears to be slightly broken , but only slightly. Pins 8 and 12 do not output (although they are not used in the sensing circuit), and I plan on getting a new Stamp ASAP. This may be the source of my problem, however, I would still like to know if there is a more fundamental issue at work here. Thanks for any help.
Unfortunately, I can’t post any pictures right now as this is my first post. I will try to get them up as soon as possible
It’s sort of long, so I’ll leave out the turning subroutines and such.
Here it is:
' {$STAMP BS2px}
' {$PBASIC 2.5}
'This linefollower program uses the voltage comparator of the BS2px microcontroller to read the inputs of five sensors.
'The program turns on one LED at a time and reads the value of the sensor that it is connected to.
'The value is compared to a constant threshold which is used to determine the presence of a black line which the robot is
'to follow.
'If the value is greater than the threshold on the right sensors then it will cause the robot to activate its left drive
'motor, turning the robot right.
'If the value is greater than the threshold on the left sensors then it will cause the robot to activate its right drive
'motor, turning the robot left.
Sensor PIN 1
Thresh PIN 2
Sensor_LED1 PIN 3
Sensor_LED2 PIN 4
Sensor_LED3 PIN 5
Sensor_LED4 PIN 6
Sensor_LED5 PIN 7
F_Dir_MR PIN 8 'Forward Direction Right Motor
R_Dir_MR PIN 9 'Reverse Direction Right Motor
F_Dir_ML PIN 10 'Forward Direction Left Motor
R_Dir_ML PIN 11 'Reverse Direction Left Motor
LED2 PIN 12
LED3 PIN 13
LED4 PIN 14
LED5 PIN 15
LED1 PIN 0
SensorValue VAR Bit 'Stores the value of the sensor as compared to the threshold voltage
RSensor VAR Bit 'Right Sensor value variable
RCSensor VAR Bit 'Right Center Sensor value variable
CSensor VAR Bit 'Center Sensor value variable
LCSensor VAR Bit 'Left Center Sensor value variable
LSensor VAR Bit 'Left Sensor value variable
PinCommand VAR Byte 'LED Sensor pin commanding variable
Temp VAR Word 'General variable for counters, timers etc. (optional)
Start:
HIGH LED1
PAUSE 200
LOW LED1
FOR PinCommand = 12 TO 15 'Do a BLiFNAR sequence while waiting to make sure sensors will register properly
HIGH PinCommand
PAUSE 200
LOW PinCommand
NEXT
FOR PinCommand = 14 TO 12
HIGH PinCommand
PAUSE 200
LOW PinCommand
NEXT
HIGH LED1
PAUSE 200
LOW LED1
CONFIGPIN PULLUP, %0000000000000010 'Set pullup resistor for sensor input
CONFIGPIN THRESHOLD, %0000000000000110 'Set logic threshold to CMOS, for easier tuning purposes
Linefollower:
DO
LOW LED1 'Turn off all LEDs
LOW LED2
LOW LED3
LOW LED4
LOW LED5
GOSUB Forward 'Go forward
GOSUB Line 'Read the value of the line sensors
IF RSensor = 1 THEN Sharp_Right 'Choose which direction to go based on sensor values
IF LSensor = 1 THEN Sharp_Left
IF RCSensor = 1 THEN Soft_Right
IF LCSensor = 1 THEN Soft_Left
IF CSensor = 1 THEN Linefollower
LOOP 'Loop again
Line:
PinCommand = 3 'Set PinCommand variable to initial state to read sensor values
FOR PinCommand = 3 TO 7 'FOR... NEXT loop that uses PinCommand as the incremental variable
HIGH PinCommand 'Activate the Sensor LED that PinCommand is equal to
COMPARE 2, SensorValue 'Compare Threshold voltage to sensor voltage as set by the trimpot - store the result in SensorValue
IF PinCommand = 3 THEN SensorValue = RSensor 'Stores SensorValue for right sensor in RSensor
IF PinCommand = 4 THEN SensorValue = RCSensor 'Stores SensorValue for right center sensor in RCSensor
IF PinCommand = 5 THEN SensorValue = CSensor 'Stores SesnorValue for center sensor in CSensor
IF PinCommand = 6 THEN SensorValue = LCSensor 'Stores SensorValue for left center sensor in LCSensor
IF PinCommand = 7 THEN SensorValue = LSensor 'Stores SensorValue for left sensor in LSensor
LOW PinCommand
NEXT
RETURN 'Go back to LINEFOLLOWER subroutine
The parts I appear to be having trouble with are the Linefollower and Line subroutines. I tried debugging the sensor values, and it only gave me 0s for all the sensors.
You did a fine job with the code writing as I was able to follow along well but it is still always hard to understand someone elese code.
I dont uderstand why you have the LEDs turn on and off in the beginning unless you are just checking to make sure everything is wired up ok?
also, this will not help if you are getting a value of 0 but you might want to try using this:
IF RSensor > 1 THEN Sharp_Right 'Choose which direction to go based on sensor values
IF LSensor > 1 THEN Sharp_Left
IF RCSensor > 1 THEN Soft_Right
IF LCSensor > 1 THEN Soft_Left
IF CSensor > 1 THEN Linefollower
The greater than will allow for the motors to work if the value is greater than one else nothing will happen if the value is say 2 or three. This is probably not an issue if the only two values returned are either a one or a zero, then the " = " operator is fine.
Perhaps you should break it down to just one sensor and try to get that comunicating rather than try all at once. Once you get one working, you can expand on that.
As to the LED sequence at the beginning: BLiFNAR = Blinky Lights For No Apparent Reason. I love flashy things! (It doesn’t serve any actual purpose, but it gives it a “cool” factor 8) )
Thank you for the suggestion for the code. The COMPARE command stores a result in a Bit Variable as either a 1 or a 0: so I guess I can’t use your method .
However, I will try checking one sensor at a time to find the problem. Thanks once again for the suggestions!
Let me know what happens with just one sensor. I would also try to have the debug widow display real time results so that you know right away if the sensors are working.
Ok, so I’ve done little work over the past few days (what with homework and all), but I have managed to get to checking the sensors. I tried checking the code, putting debugs after every new subroutine, and to show the values of the sensors, and still nothing. I’m wondering if I’ve wired the sensors incorrectly, so here is a schematic of what I’m doing:
PIN 1 and PIN 2 are comparator input pins. The potentiometer acts as a voltage divider to produce an adjustable threshold (I’ve tried adjusting it all the way from limit to limit, still doesn’t work). The T(x) and D(x) pairs are the QRD1114s.
I’m still getting a zero value fr every sensor, however when using my video camera I did notice that the IR LEDs of the QRD1114s were flashing when they were supposed to, so I don’t think the sensors are damaged.
You must be turning on the sensors individually, and reading them back in multiplexed on a single line. Thru me for a while! I’d have left 'em all on, and watched the 5 outputs individually, but that’s just me.
Jon picked up the individual series resistors for the LEDs already.
Sorry Jon, I forgot to draw in the current limiting resistors i already have on the IR LEDs. Thanks for pointing that out though.
The BS2px automatically outputs either a 1 or a 0, depending on if input voltage 1 is greater or less than input voltage 2. I’m using a CMOS logic threshold level for this project, so 1 would be 2.5 V or greater and 0 would be less than 2.5V. As such, I don’t think I can directly read the voltage on the input of the stamp, sorry.
You’re absolutely right, KM6VV, and the only reason I didn’t choose to do them separately is that the BS2px only has one comparator input pin. Maybe if I make another one, and use some voltage comparator chips…
Actually, that’s what the 10K resistor in the schematic is for. It creates a voltage divider between itself and the QRD1114, which can then be fed to the comparator. parallax.com/Portals/0/Downl … /nv116.pdf
Follow this link, and on page 4 you’ll see the schematic I based my robot on.
Um, what… You put the black lead on the ground and the red lead on pin one in your posted schematic. You really need to know the voltages present if you want to troubleshoot your problem. Hope this helps, Jim
I understand, you’re using a comparator instead of an A/D. What I’m telling you is with the appropriate pullup resistor, the output from the sensor itself is a digital signal, at least as far as line follower/mini sumo usage goes.
The values end up being about 0.2 volts and 4.6 volts (for black and white, don’t remember which is which). Thus the output from the sensor can go directly to the input pin on your stamp.
I’ve never seen a set of sensors like this hooked up to one input, and I can’t really say I understand why you would want to do it this way for a line follower.
Typically, with a 5-sensor line follower, you have each sensor hooked up independently, and thus can read each sensor independently, so you can see if the robot is starting to veer off being centered on the line.
To do it that way, you need one pullup resistor and one current limited resistor for each sensor.
You should be feeding the LED with 5 volts, and the pullup should be connected to 5 volts as well.
it’s no real difference. I mean it takes the same number of I/O piuns either way…
The V+ must be connected directly to a 6vdc battery? You should have it connected to 5vdc. What’s the comparitor supply voltage?
From what I am seeing the sensors are working great, but the comparitor is not. If the comparitor is powered up at 5vdc then there is a problem with putting 6vdc + on one of the inputs.
, but only slightly. Pins 8 and 12 do not output (although they are not used in the sensing circuit), and I plan on getting a new Stamp ASAP. This may be the source of my problem, however, I would still like to know if there is a more fundamental issue at work here. Thanks for any help.
.
You put the black lead on the ground and the red lead on pin one in your posted schematic. You really need to know the voltages present if you want to troubleshoot your problem. Hope this helps, Jim