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Servo Tester Modified:

 








Servo Tester, readily available and ripe for modification and connecting to DCC devices.

Do check with the vendor before purchasing, their are least two variants available, one which upon power on, will go through the complete test routine including moving any attached Servos, this one is best avoided, and go for the other type, which upon power on does not 'cycle' through the routines.


















Bottom view of the Servo Tester.









Modification of the Servo Tester, requires soldering two wires to the underside of the PCB.

One wire to the middle connection of the Potentiometer, and the other to the GND connection.









The two wires can then be connected to a On/Off switch, or a Optocoupler. 

To operate the Servo, by closing the switch, the connection to GND is complete, Servo moves to the end point position as set by the Potentiometer on the Servo Tester. 

By opening the switch, Servo moves back to it's starting position. 





















RECOM, 5V Voltage supply.














Optocoupler, for connection between decoder output, to input of the modified Servo Tester.

Host decoder is a LGB 55021, which has no onboard facilities to control a Servo.





















Individual sections, 5V power supply, Optocoupler and Modified Servo Tester.
 
Switch action of opening and closing is replaced by the LGB 55021 Function Output connected to the Optocoupler, activation by the F1 Key on the Handset. 

Function Key pressed as in ON, Servo moves to the end point as set, Function Key pressed again, Servo returns to the start point.


 Individual parts, amalgamated and built on a single Stripboard PCB. 




 
Above pictures of the Servo in action.

Alternative ideas to assist with construction:
5V regulated power supply, recent Blog Post here, on the LM2596 module.

Optocoupler:
Used the two following modules for various projects.



















Only provisio on the one above, that for long term continuous use, the 3.3K Ohm will get warm, may need to change it out for a resistor with a higher Watt rating. 





























Optocoupler as above, Remove the Yellow Jumper, to preserve both sides of the circuit for electrical isolation.


 


















































Note the position of the Yellow jumper.














24V DPDT Relay Module.














Underside of the Relay module PCB.














Connections to the decoder, RED VCC to Decoder (Dek +), Orange to T and GND on the Relay Module,  to the decoder Function Output.















































Salvaged and recycled 24V SPST Relay (Ex British Gas from the Room Thermostat from the old central heating system)

Cover removed to show the internal coil, NOTE the diode, omit to install this, then any decoder that has a Relay connected to a Decoder Function Output, will have a very short life span!




























Further reading:
Idea borrowed for the Modified Servo Tester from a Blog Posting by Rik of  the Peckforton Light Railway.