Solar Tracking kit
Price - Stock No 217 

 Motors with Gearboxes
Price - Stock No 750 3v Gearbox 2.93RPM - 3000 RPM (6 configurations)
Price - Stock No 751 12V Gearbox 36 RPM
Price - Stock No 752 12V Gearbox 70 RPM
Price - Stock No 753 12V Gearbox 160 RPM

This kit is designed to follow the sun or move towards the brightest thing. 

This kit monitors the position of the sun using two Light Dependant Resistors (LDR's), and makes the decision to move towards the brightest light source adjusting it's path continuously.

IC1 - LM1458



  1. To  make up the Kit, firstly check the PC Board for any damage. Check continuity of all tracks  with  a  multimeter  or  an  electronic circuit tester.
  2. Identify the resistors using a multimeter or the Resistor Colour Chart
  3. The three resistors can be bent to shape and fitted,
  4. Solder in place - see Soldering Technique.
  5. The two diodes are polarised so care needs to be taken to position and orientate correctly, solder in place.
  6. The IC socket can be carefully pushed into place. Ensure all the pins of the socket have come through the PCB and solder in place.  
  7. The two trimpots are different, identify, push in place and solder.
  8. Pins are provided to terminate the input and output wires, and the switch.  Insert and solder the pins. 
  9. Use the above diagrams to orientate and insert the two transistors.  Solder in place.
  10. The LDR's need to be offset from one another.  This angle facilitates the direction finding capability.  Trim one leg of one LDR, solder this leg to the other LDR to create the 'LDR offset' above. Solder the 'LDR offset' in position.
  11. Cut the figure 8 wire into three appropriate lengths - one for each motor and one for power input .  Strip and tin the wire - see Tinning wire.
  12. Solder one wire to the voltage input.
  13. Note the '+' signs on two of the motor terminals on the PCB Layout Diagram.  Depending on your locomotion method, you need to determine which way to connect each motor so that it moves in a forward direction.  Using a suitable power source for your motor, connect it so that it moves in a forward motion, note which terminal you have connected to positive.  With this determined, connect each motor with this 'positive to go forward' to the pin with the '+'.  Connect the other motor terminals to the respective pins.  
  14. You will find that the legs of the IC are spread too wide to fit into the socket.  Place the four legs on one side of the IC on  the  table and  push gently so they are bent in slightly.  Repeat for the other side. Find the locating DOT on the top surface of the IC, turn it so it matches the placement diagram and push it into its socket.


Setup and Testing

  1. Check the supply voltage, we will call this +V
  2.  Adjust both trimpots to a position of approximatly 1:30.  This is the initial setting
  3. With the LDR's pointing to a bright light, connect the supply voltage.   Both Motors should run.
  4. Check for correct operation by shading each LDR in turn - checking that each motor stops.  Shading the right LDR will stop the left motor and vice versa.

The 100 K trimpot sets the balance point.
The 20K trimpot sets the sensitivity.

Technical Notes

If we look at the schematic, and particularly the motor control, the forward and reverse is achieved when the outputs of IC1a and IC1b are in different states.  A truth table helps explain this:

IC1a Output IC1b Output Motor Behaviour
Low Low

Right FWD, Left FWD

Low High Right STOP, Left FWD
High High N/A
High Low Right FWD, Left STOP

The transistors enguage each motor when a low signal is outpt from it's respective operational amplifier. See Transistors.

The two power diodes protect the transistors from the voltage created by the motor in the instant(s) after the motor has been stopped.  As the motor still has angular momentum, it will generate a voltage and current (Power).  This power is capable of destroying the transistors and is bled off via the diodes.  See Diodes.

The input stage uses two operational amplifiers (contained in IC1) to make a decision on the direction of light.  The op-amps are fed by the junction of the LDR's.  If both LDR's see the same amount of light, their resistance is equal.  The junction of the LDR's would be at input voltage divided by two ie. 12V input - junction of LDR's at 6V.  If the light on one LDR is greater than the other, than the voltage will move, higher or lower depending on which LDR has more light.

Limits are set by the four resistors in series from +V to 0V, and adjusted by the two trimpots.  If the voltage moves outside these limits, the respective op-amp will activate the motor and move appropriatly.

The 20K trimpot sets the sensitivity ie. the distance between these limits.  The 100K trimpot adjusts so that these limits are symetrical around +V/2 (balance point).


For more information on the LM1458 see Datasheet for the LM1458.  


Troubleshooting will consist of:

Contact CdS electronics

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