The next module that needs of a controller is the shaker liner guide. This controller is going to be very easy compared to the previous 2, because it only needs to control the direction of a DC motor. I added also a linear DC motor speed controller, to reduce the speed. The speed is controlled by a potentiometer on the PCB.

Here is the schematic diagram of the circuit (as always, click to enlarge):

I use 2 relays to control the motor. The first relay (K1) turns on and off the motor and is driven through Q2. The next relay, K2, will change the polarity of the motor, and thus it controls the direction. This relay is controlled through Q3.

The transistor Q1 is the one that controls the voltage of the motor. This is done by adjusting the potentiometer R4.

Finally, R5, R6 and the zener D1 are used for the encoder. The signal of the encoder is 12 volts. The zener will drop it down to 5 volts (for HIGH state), and the R6 is pull-down resistor, as the signal will be driven to the master microcontroller. R5 is current limiting to protect the Zener.

I will not go through the whole procedure that i do to make a PCB, as i have already show this in the previous pages. So, here is the PCB complete, with all the components soldered:

The motor draws about 2.5 Amperes at 12 volts. That is 30 Watts. The transistor Q1 needs of a large heat-sink to operate, as it needs to dissipate a lot of power when working. What i really did, is to cut a 16x10mm aluminum U profile, about 30mm long, and use it as a heat sink. It is not a perfect solution, but hey, the motor will only run for a couple of seconds each time. I tested this heat-sink for about 2 minutes of continuous operation, and proved to be quite reliable. No need to mention that i could easily bake eggs on it...

Then, i began wiring the limit switches:

The tools that i used	First the bottom limit switch	And then the top limit	Both switches goes to the PCB using a polarized pins header

The controller works perfect. When 5volts (hight is applied to the "start" pin, the motor goes down with the pre-selected speed. If the limit switch is actuated, the motor stops immediately, and the "Bottom Limit" output is driven low. The motor can only move upwards.

When the "direction" pin is high (5 volts), the motor moves upwards, until the top limit is actuated. The motor will then stop, and it will only be able to move downwards. Moreover, the "top limit" output will be driven low.

The encoder interface also works fine. The pulses are successfully converted form 3-12V to 0-5 volts.

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