Servos


Seems as if a typical servo motor, the kind that you put in a little aircraft to turn the flaps and other moving parts, likes a pulse or "signal" every 20ms (50Hz) and keeping it high for 1ms will drive it to the one side and a pulse 2ms long will drive it to the other side. The 9G is a popular choice for throwing turnouts (6V), and at $2.69 (2013) hard to beat! The even smaller 1.7G linear servo motor (4.2V) at $4.29 (2013) is also amazing to see in action.

Servo motors of all kinds for very little money at HobbyKing . com! You order them and forget about it, weeks in the future, you get a surprise delivery!!!

Far left:    
Far right:    

So the quest is to see how many of these devices we can control with a single 28 pin PIC16F chip. Well, we got distracted and opted for 2 servos controlled by 1 PIC10F! 6 pins, with two inputs and two servo outputs. Power and ground. 30 degree swing, good enough! For N-Scale you only need to move the points 1mm, so use the first hole on the horn, closest to the center of the circle. HO-Scale, maybe use the 2nd or 3rd hole, but you might want to mount the servo a little lower so that your piano wire can be long after the downwards bend to create a little bit of a "spring" effect. If you block the servo, it will sit there and create a noise, trying to push further. With a "spring", it can go further and stop making that noise, while the points are already thrown.

A very special note though, the 5V power pin on the board does not match the pin out of a regular servo motor, the control line is in the middle. So you need to swap the red and white (or control) wire in the connector that is connected to the servo motor.


(notice the swapped red and white wire?)

The connectors are all in a square U shape. Ends of the U are the GND pins for the two servos, below that the CTRL pins and then the 5V or Vcc pins. Looking at the upside down U in the photo above, the power and input connector is at the top now, with the 5V supply, then Ctrl-Left-Input, Ctrl-Right-Input and GND (by the negative lead of the capacitor). And again, from top to bottom now, left side as well as right side: Vcc, Ctrl and Gnd, for each servo. The pdf file shown at the bottom, also show the board layout and pinout diagram.

The Ctrl-(Left/Right)-Inputs have 1k ohm pull up resistors on board, so all you need to do is add a toggle switch to connect the input to Gnd in order to make the servo go the other direction!

The following diagrams shows how to wire in two LEDs, resistors (about 5k and 4k (since 1k is on the board already)) and a Toggle switch (SW1, far left) to also show which way the turnout might be thrown:

Toggle off (or input not connected)


Toggle on (or input connected Gnd)


So, swap the white and red wire on the servo connecter side, then pug the connector in with the Gnd (black wire) to the edge of the board. Provide 5V and Gnd (big blue capacitor side) to the top row (green LED will show power) and a tweezer short between one of the middle Ctrl-Input pins should move your servo!


Or use an Arduino! (MERG members, also read this)
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Gert (TxAdmin) Muller,
Sep 15, 2014, 2:32 PM
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