Sorry I do not have any pictures of this yet. I just got batteries for my camera this morning before work.
This consists of:
2x Fairchild QRD1114 Reflective Object Sensors
2x 10kΩ resistors
1x 180Ω resistor
2x PNP transistors
2x GM2 motors
The idea behind this is pretty simple. When the QRD1114 sensor sees the reflected IR light it has emitted, the phototransistor closes and sends current through to the PNP transistor which then closes and sends current through to the motor. When the QRD1114 sensor does not see the reflected IR light it has emitted, the phototransistor opens sending no current through to the PNP transistor. The 10kΩ pull-up resistor keeps the PNP transistor open, so that no current flows through to the motor causing it to stop.
When the QRD1114 sensor is pointing on the white background, the emitted IR light is reflected back, and the sensor closes. When the QRD1114 is pointing on the black line, the emitted IR light is NOT reflected back and the sensor opens.
The left QRD1114 sensor is connected to the left motor through the left PNP transistor. The right QRD1114 sensor is connected to the right motor through the right PNP transistor.
The 180Ω resistor is for the 2 IR LEDs inside the 2 QRD1114 sensors.
UPDATE:
Schematic has changed, PNP transistors were apparently upside down.
This is a companion discussion topic for the original entry at https://community.robotshop.com/robots/show/brainless-line-following-robot
kinda like a beam robot but
kinda like a beam robot but without the solar panels.
**the one above **
the one above
i guess its not that close but the whole no brain thing reminds of BEAM robotics
Either your motor+transistor
Either your motor+transistor circuit is wired backwards you you wanted NPN transistors instead. As it’s shown in the diagram, the PNP transistors won’t allow current into the motor. Current always flows through a BJT in the direction of the arrow. You either need to swap the PNPs out for NPNs, or connect the PNP emitter to your +5V and connect the other end of the motor to ground.
Maybe I worded the "allows
Maybe I worded the “allows current” wrong. I do not need NPN transistors because the QRD1114 is connected to 0v and gives 0v when it is on white. If it was connected to 5v, then yes, I would need a NPN transistor, but this set up requires PNP. Try it out. 
At the very least the PNP
At the very least the PNP transistors in the diagram are upside down - current is normally passed in the direction of the arrow. Reverse biasing the collector-emitter junction can damage the transistor.
**Upside down? How so? **
Upside down? How so? Doesnt current flow from emitter to collector? The diagram shows E(mitter) is at Ground/0v and C(ollector) is connected to the motor. I would think that shows current from 0v to motor.
Not sure if you are refering to the NPN transistors in the QRD1114 sensor. According to HVWTech.com (http://www.hvwtech.com/products_view.asp?ProductID=97) the sensor is hooked up correctly.
I love the idea of a line
I love the idea of a line following robot without a MCU, but I never heard of this sesnor. Do you know where to buy one?
I think youre getting
I think youre getting confused by the 2 different current flow hoo-haa`s. My understanding is that electrons flow from negative to positive, but thinking generically of "power", you say it comes from positive. "Power" from positive goes against the arrow into ground in your schematic.
That part of the schematic
That part of the schematic came from HVWTech.com (http://www.hvwtech.com/products_view.asp?ProductID=97) where it shows how to hook up the sensor. Yes, I agree, it does look odd/different, but that is where I saw how to hook it up and did so.
I meant the motor
I meant the motor transistors, not the sensors.
So the +5v is flowing to the
So the +5v is flowing to the 0v?
So then the Motor would need to connect to the Emitter and the 0v to the Collector?
Sorry TeleFox, you were
Sorry TeleFox, you were correct in that. I am very new to electronics. Thank you for the correction.
I picked up a few of these
I picked up a few of these sensors a while back from Solarbotics myself - I was ordering some other parts and they were just too cheap to say no too =D
With a bit of calibration you can even make them into modulated IR proximity detectors, and although the range is pretty short, they’re a lot more compact than building your own from discrete LEDs and phototransistors.
No worries about the mistake Rich, we’re here to help after all.
Haha, I did the same
Haha, I did the same thing. I was ordering up a bunch of gear motors and the shipping was pretty steep for next day so I just added more.
**brainless line follower **
i agree on your idea done went and got the parts going to finish first one by orginal schematic then going to try one other way but the transistors are backwards on schematic
Looks good. Just be sure to
Looks good. Just be sure to select PNP transistors that can handle the current of your motors.
Making it Better
I was looking ar these schematics and I think I found a cheaper and more effecient way of making it. Instead of using the fairchild sensors, why not just use a ir emitter and a phototransistor since that is what the sensor is. I was also looking at that you only had one sensor for each side. I think a pair of sensors on each side would be better. These would act like a “safety net” if the first ones didn’t pick it up. You could also put in a center of switch to act as an on/off switch. With this you could swap the motors and make it follow dark line on a light service and vice versa.
https://www.robotshop.com/letsmakerobots/node/16705
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