Servo Kit Assembly

Servo Kit Assembly
d. bodnar 9-19-12 & 9-16-15

New! Click here for software modifications!

The following parts are needed to assemble the servo controller.

Two potentiometers (top left)
circuit board
14 pin socket - even though we are likely to use an 8 pin device a 14 pin PIC or PICAXE can be used
capacitor -.1 mf - 3 mf tantalum (right of board - may vary from photo)
7805 voltage regulator (3 pin device right of cap)
red power LED
510 ohm resistor (top one - blue body)
2 @ 10 K resistor (brown-black-orange) - only 1 for the PIC processor version
22 K resistor (red-red-orange) - not used with the PIC processor version
2 @ two pin header
2 @ three pin header- only 1 for the PIC processor version
wire for power connection (not shown here)
PICAXE 08M (not shown here)

This is the board for the newer revision. Construction is the same.

Step 1: Assemble the power supply.

red and black wires to + and - contacts as shown
capacitor - longer lead "+" to left and shorter lead to hole that goes to black power lead - note that some caps that are supplied with the kit have equal length leads - the positive terminal is marked with a + sign.
7805 - make sure it faces as shown
510 ohm resistor
red LED - longer lead (positive) to left as shown - flat spot (minus) goes right

Solder carefully watching out for solder bridges - examine frequently with a magnifying glass.

After soldering apply power (8-12 volts DC) to the red and black wires - the red LED should light. If it does not check for proper parts placement and shorts.

Step 3:

Insert the socket. Make sure the end with the round notch cut in it goes to the right as shown.
Insert the three pin programming header (NOTE: not used with the PIC version)
Insert the two 10 K resistors and the 22 K as shown. The 22 K is between the two 10 Ks.
(NOTE: only one 10K resistor is used with the PIC version - Install only the 10K resistor that is to the left - the two resistors to the right and the 3 pin header are not needed)
Solder - check for bridges

Apply power again and make sure the LED still works.

Step 4:

Insert and solder the trigger and sound headers

Step 5:

Insert and solder the two pots

Check the power LED once more. If you have a volt meter confirm that pin 1 on the socket (upper right in the photo above) has 5 volts on it and that lower right pin on the socket is ground. Disconnect power when done.

Step 6:

Insert and solder the servo connection header
Carefully insert the PICAXE processor. The notch in the chip has to go at the same end as the notch in the socket. In this photo the notch goes to the left.

Here is the layout on the newer (8-09) board - note that they are virtually identical except for the mounting holes.

Briefly apply power and confirm that the LED lights properly.

This completes assembly - note that there are a number of unused connections on this board.

Initial Testing:

Insert the servo plug as shown. The black wire must go to the left.

Set the two pots as shown. The "Start" pot on the left goes all the way counter clockwise and the "Range" pot on the right goes all the way clockwise.

Apply power and short out the two Trigger pins (upper right)
The servo should go from one extreme of its movement to the other, approximately 180 degrees of rotation.
Adjust the pots as below and you should see a change to about 90 degrees of movement
Adjusting the "Start" pot will change the starting point but the range will stay at 90 degrees
Adjusting the "Range" pot will change how far the servo goes from the start position.

Note that there are positions where the servo will not move as shown below.

The sound pin (the one closest to the "d" in "Sound") goes "high" for a moment when the trigger is closed. This connection can be used to start a sound card or to light an LED. The other pin in the sound pair goes to ground.

Quick Connectors for Headers

You can salvage connectors from an old PC that will fit right onto the 2 and 3 pin headers on the circuit board. You can also cut up an IC socket into sections that will fit onto the pins. Wires can then be soldered to the socket pins.

Program Modifications

Some users of the servo board have requested software modifications. Some variations on the original program are shown below with their characteristics.

Original program. One button push starts a complete cycle of servo motion from one extreme to the other and back to the original position with a 1.5 second pause between.

SYMBOL CCWMax = 200 '225 manual recommended max
SYMBOL CWMin = 30 '75 manual recommended min
SYMBOL RangeMax = 170
SYMBOL Temp = b0
SYMBOL Range = w5 'max to min range
SYMBOL CCW = w6 'where to start rotation
SYMBOL CW = b3
SYMBOL Temp2 = b5
SYMBOL Delay = 15
SYMBOL Audio = 0
SYMBOL ServoPin = 4
SYMBOL Trigger = pin3

Start:
LOW ServoPin 'relax servo
IF Trigger = 0 THEN Start ' wait till button pressed

HIGH Audio
GOSUB GetPots:
FOR Temp = CCW TO CW Step -1
SERVO ServoPin, Temp
PAUSE Delay
NEXT Temp

LOW Audio
pause 1500

GOSUB GetPots
FOR Temp=CW TO CCW Step 1
SERVO ServoPin, Temp
PAUSE Delay
NEXT Temp
PAUSE 1500
GOTO Start:

GetPots:
READADC10 2, Range
Range=1023-Range
Range=Range/6
READADC10 1, CCW
CCW=CCW/6 + 30
Temp2=Range+CWMin
IF CCW <Temp2 THEN Skipover
CW=CCW - Range MIN CWMin
GOTO Skipover2

Skipover:
CW = CWMIN

Skipover2:
RETURN

Modification #1
Objective - in stead of the servo going starting from a button push and going from one extreme of its movement, pausing for a few seconds and returning to its original position two button pushes are needed. The first push has the servo move to its one extreme where it stays till the button is pressed again.

SYMBOL CCWMax = 200 '225 manual recommended max
SYMBOL CWMin = 30 '75 manual recommended min
SYMBOL RangeMax = 170
SYMBOL Temp = b0
SYMBOL Range = w5 'max to min range
SYMBOL CCW = w6 'where to start rotation
SYMBOL CW = b3
SYMBOL Temp2 = b5
SYMBOL Delay = 15
SYMBOL Audio = 0
SYMBOL ServoPin = 4
SYMBOL Trigger = pin3

Start:
LOW ServoPin 'relax servo
IF Trigger = 0 THEN Start ' wait till button pressed

HIGH Audio
GOSUB GetPots:
FOR Temp = CCW TO CW Step -1
SERVO ServoPin, Temp
PAUSE Delay
NEXT Temp

LOW Audio
StayHere:
IF Trigger = 0 then StayHere:

GOSUB GetPots
FOR Temp=CW TO CCW Step 1
SERVO ServoPin, Temp
PAUSE Delay
NEXT Temp
GOTO Start:

GetPots:
READADC10 2, Range
Range=1023-Range
Range=Range/6
READADC10 1, CCW
CCW=CCW/6 + 30
Temp2=Range+CWMin
IF CCW <Temp2 THEN Skipover
CW=CCW - Range MIN CWMin
GOTO Skipover2

Skipover:
CW = CWMIN

Skipover2:
RETURN

Program - revised to use SERVOPOS command - may reduce "chatter"

SYMBOL CCWMax = 200 '225 manual recommended max
SYMBOL CWMin = 30 '75 manual recommended min
SYMBOL RangeMax = 170
SYMBOL Temp = b0
SYMBOL Range = w5 'max to min range
SYMBOL CCW = w6 'where to start rotation
SYMBOL CW = b3
SYMBOL Temp2 = b5
SYMBOL Delay = 15
SYMBOL Audio = 0
SYMBOL ServoPin = 4
SYMBOL Trigger = pin3

Start:
LOW ServoPin 'relax servo
IF Trigger = 0 THEN Start ' wait till button pressed

HIGH Audio
GOSUB GetPots:
SERVO ServoPin, CCW
FOR Temp = CCW TO CW Step -1
SERVOPOS ServoPin, Temp
PAUSE Delay
NEXT Temp

LOW Audio
pause 1500

GOSUB GetPots
SERVO ServoPin, CW
FOR Temp=CW TO CCW Step 1
SERVOPOS ServoPin, Temp
PAUSE Delay
NEXT Temp
PAUSE 1500
GOTO Start:

GetPots:
READADC10 2, Range
Range=1023-Range
Range=Range/6':Range=Range*2
READADC10 1, CCW
CCW=CCW/6 + 30':CCW=CCW*2 + 30
Temp2=Range+CWMin
IF CCW <Temp2 THEN Skipover
CW=CCW - Range MIN CWMin
GOTO Skipover2

Skipover:
CW = CWMIN

Skipover2:
RETURN

The code below is not designed to work with the board in this kit but it does contain some routines that might be used. It was developed by Kevin Rogers. The program is designed to lower and raise arms on a crossing and flash crossing lights when a train crosses one of two light sensors - when the 2nd light sensor is crossed the crossing arms raise and the flashing stops.

start0:

#PICAXE 14M2

;Define Outputs use portB pins

SYMBOL Light1 = b.1 'pin 12

SYMBOL Light2 = b.2 'pin 11

SYMBOL Light3 = b.3 'pin 10

SYMBOL Gong = b.4 'pin 9

SYMBOL boom1 = b.5 'pin 8

;Define inputs use portC pins

SYMBOL LDR_1 = c.0 'pin 7

SYMBOL LDR_2 = c.4 'pin 3

'Define variables

SYMBOL boompositn = b1

SYMBOL currentpos = b2

SYMBOL Flasherflag = b3

SYMBOL Lightlevel1 = b5 ; select a spare variable b5 here

SYMBOL LightLevel2 = b6

;define constants

SYMBOL BoomSpDelay = 60 'ms

SYMBOL FlashDelay = 500 'ms

SYMBOL Setpoint1 = 60 ; 0 to 255 is ADC input range - this is the trigger level for lights to flash

SYMBOL Setpoint2 = 60 ; 0 to 255 is ADC input range - this is the trigger level for lights to flash

SYMBOL BoomIsUp = 120

SYMBOL BoomIsDown = 218

; first code section is for boom control

init:

servo boom1,120 ; initialize servo

currentpos = BoomIsUp

BoomCtrl:

READADC LDR_1, LightLevel1 ; check light level at side 1

READADC LDR_2, LightLevel2 ; check light level at side 2

IF currentpos = BoomIsUp THEN

IF LightLevel1 > Setpoint1 OR LightLevel2 > Setpoint2 THEN ; if train is detected at either sensor

PAUSE FlashDelay ; wait a while (say 2 flash periods) so lights flash before the boom starts to lower

PAUSE FlashDelay

FOR boompositn = BoomIsUp TO BoomIsDown ; lower the boom in increments

SERVOPOS boom1, boompositn ; move to next incremental position

PAUSE BoomSpDelay ; delay to give slower boom travel speed

NEXT boompositn

currentpos = BoomIsDown ; set the current boom position as down

ENDIF

IF currentpos = BoomIsDown THEN

IF LightLevel1 < Setpoint1 AND LightLevel2 < Setpoint2 THEN ; if train is clear of both sensors

FOR boompositn = BoomIsDown to BoomIsUp STEP - 1 ; raise the boom in increments

SERVOPOS boom1, boompositn

PAUSE BoomSpDelay

NEXT boompositn

currentpos = BoomIsUp ; set the current boom position as up

ENDIF

GOTO BoomCtrl

;==========================================================

; run the flashing lights as a separate process

Start1:

LOW Light1 ; turn off all lights and bell/gong

LOW Light2

low Light3

LOW Gong

LightCtrl:

IF LightLevel1 > Setpoint1 OR LightLevel2 > Setpoint2 THEN ; start flashing the lights as boom about to be lowered

IF Flasherflag = 0 THEN ; set for first time only in each boom down - up cycle

HIGH Light1

LOW Light2

HIGH Light3

Flasherflag = 4 ; any non zero value - to flag not to repeat

ENDIF

PAUSE FlashDelay

HIGH Gong

TOGGLE Light1 ; flash each light alternately

TOGGLE Light2

PAUSE FlashDelay

LOW Gong

LOOP UNTIL LightLevel1 < Setpoint1 AND LightLevel2 < Setpoint2 AND currentpos = BoomIsUp

ENDIF

IF Flasherflag = 4 THEN ; when the boom is fully raised

FOR Flasherflag = 4 to 1 step -1 ; flash lights for a few more cycles after the boom is down

PAUSE FlashDelay ; don't change the sequence 3 to 1 or will need to add b3 = 0 after the NEXT command

HIGH Gong

TOGGLE Light1 ; flash each light alternately

TOGGLE Light2

PAUSE FlashDelay

LOW Gong

NEXT Flasherflag ; on exit b3 = 0 ready for the next cycle

LOW Light1 ; turn off all lights

LOW Light2

LOW Light3

ENDIF

GOTO LightCtrl