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Octad Servo Driver


The OctadServo is based on the MGV84. Instead of controlling 4 servo motors the Octad is able to control 8 servo motors. The Octad has 8 isolated inputs which will each be activated by supplying 5V dc. The Octad is provided with 8 relays, to switch the turnout frogs.Instead of setting up the servospeed, like the MGV84, the middle position of the servo is adjustable. In stead of the MGV84 there are no outputs for feedback. The board is a D.I.Y. project and there are no boards available.


For each turnout there are three individual settings to be made:

  • The middle position of the servo
  • The total angle, adjustable betwee 10 and 40 degrees.
  • The position of the relay, normal or reverse.


  • relay for each turnout frog
  • bistable relay to reduce power consumption
  • isolated input to avoid ground loops


To set the parameters follow the next steps: - Make all necessary connections to Octad.

  1. Shut off power to Octad.
  2. Shut off all 8 inputs (if already on)
  3. Connect servomotors to Octad
  4. Set jumper Jp2
  5. Power up Octad.
  6. the unit is now in adjust mode.
  7. Activate 1 of the 8 inputs.
  8. The corresponding servo will now run up and down.
  9. The middle position of motor can be changed by P1. NOTE: changing will only occur after the motor has been in the left limit position.
  10. The angle of the motor can be adjusted by P2. NOTE: changing the angle will only occur after the motor has been in the left limit position.
  11. The relay for the turnout frog will change position, when the servomotor passes the middle position.This relay-position can be reversed by setting/removing the jumper Jp2
  12. When motor runs to satisfaction and relay position has proven to be correct, inactivate input.
  13. Before activating an other input, and before powering off, wait until servo has come to rest.
  14. The parameters will be stored and the motor will stop in left limit position.
  15. Proceed, if necessary, with the other servo motors, starting at item 8.

After all servo motors are set, shut off power, and remove (if set) jumper Jp2. Then turnon Octad power.

The unit is now ready for use.


Firmware, KiCad etc:

Bill of materials

Part nr Description
C1 1000uF
C2 100uF
C3 100uF
C4 100n
C5 C6 18pF
D1 B80C1500
D2 - D17 1n4148
K2 - K9 CONN_3
K10 - K17 RALD5W-K
K18 - K20 CONN_3
P1 - P3 CONN_2
P4 -P5 CONN_4
R1 - R8 1k
R9 - R11 10k
R12 - R13 3k3
R14,16,18,20,22,24,26,28 2k2
R15,17,19,21,23,25,27,29 270
RR1 8x10k
RV1 - RV1 10k
U2 - U3 7805
U4 PIC16F873
U5 - U6 PCF8574AP
X1 20Mhz
octad-servo-driver-en.txt · Last modified: 2019/05/05 00:47 by rainerk