Zombie Line Follower 7.0

 

 Schematic update in progress.

I saw someone else had the idea of a brainless line following robot. The creator of it was BigRick. Click on the link to see his design. https://www.robotshop.com/letsmakerobots/node/8396. This was my insperation to create the Zombie Line Follower. I was looking at his and I saw some ways to improve it. Instead of only two sensors why not have four. The extra sensor act like "Safety Net" incase the first pair miss it. There is also a variable resistor to control the ir emitter to dim and to bright. The sixty-five ohm resistor acts as a "Safety Net" if you where to turn it all the way down. The toggle switch is wired to swap the motor to change line color such as a black line with a white background and vice versa. To build follow theschematics at the top of the page. There is two 150Ω resistors missing. These would be in front of the colored L.E.D.s.

Componant List:

  • 4x Fairchild QRD1114 Reflective Object Sensors or ir emitter and transistor
  • 2x 10kΩ resistors
  • 1x 65Ω resistor
  • 2x PNP transistors
  • 1x Toggle Switch
  • 2x DC motors
  • 1x 9V Battery holder
  • 3x colored l.e.d.s
  • 3x colored l.e.d.s
  • 1x 5v voltage regulater

 

                  
This is the wired toggle switch to         This is the backside of the                   This is the front sid of the unfinished

pick preferences and for power.          unfinished circuit board                      circuit board

 

 

Follows Light and Dark Lines

  • Actuators / output devices: 2 geared motors
  • Control method: autonomous
  • CPU: none
  • Operating system: none
  • Power source: 9v battery
  • Programming language: none
  • Sensors / input devices: IR phototransistor
  • Target environment: indoor

This is a companion discussion topic for the original entry at https://community.robotshop.com/robots/show/zombie-line-follower-7-0

Schematic

I do not understand how this design can work.

Works
This works because the PNP transistor turns on when negative power is supplied. As you may see there are two pairs of photo transistors per side. These close and open the circuit there for applying negative power to the PNP powering the motor.

The base of the PNP appears

The base of the PNP appears to be held at 5V by the 5V regulator. You seem to be dropping, or attempting to drop, 4V across the base/emitter junction.

The junction of the 10k resistor and the phototransistors may vary with the light level, but this will not affect the voltage on the base of the PNP.

The voltage across the motors will be clamped by the diodes in parallel.

 

Oops
I just realized that. I am fixing the schematics as I am writing this hope to have them up by Saterday.

What did you update or
What did you update or change… This looks exactly the same as the last post.

Please, if you do not have a
Please, if you do not have a robot yet, post it as a blog entry. Please read the rules, top menu.

The schematics
The PNP Transistor was hooked up wrong. Sorry.

This is not a robot… Stop
This is not a robot… Stop updating it!

Here is some pics

Look up top

 

Design problems

Towlieboy78, there are still a few problems with your design. Have you breadboarded and tested it?

I see you are intending to vary the PNP base resistance to vary the emitter/collector current, and hence the motor speed. This is a poor method of control which wastes power (as heat in the trasistor), and is heavily dependant on the beta of the transistor.

You should be trying for an on/off control of the motors. This would be best implemented with a pulse-width-modulation circuit, but your simple design should try to steer the robot by turning off one motor at a time to correct its heading.

By connecting the base of the PNP to the junction of the 10k resistor and the phototransistors, and tweaking the value of the resistor, you should be able to achieve a sharp on/off action of the motors as the light level varies. A two transistor arrangement would be better, but you should try this first.

The other major problem is that you still have three LEDs in parallel with each motor. Assuming these are red LEDs, with a forward voltage drop of around 2V each, the voltage across your motors will be clamped at 6V. The rest of the voltage (~3V) will be dropped across the PNP transistor. If you intend these LEDs to show which motor is currently active, please place a current limiting resistor in series with them.

How about a 150 ohm transistor
Would that work

LED resistor

I = V/R = 3/150 = 0.02 amps, or 20 milliamps. This is ok.

EDIT: removed subcircuit.