Prog Examples

Circuit Description

This circuit senses a voltage change across a thermistor, and switches a relay when the temperature reaches a programmable point. The switch-point is adjustable, and the test operator is to adjust the threshold for a given temperature. For this configuration, the operator must adjust R12 for the relay to switch at 3.8 volts.

There is some logic on this board as well. Connector J1 contains all the input lines for the logic. If there is a low on pin 4 of J1, LED D3 will light. This same line feeds the "D" input of the flip-flop U3. Whenever the clock (pin 3, U3) goes high, the value at "D" will be transferred to the "Q" output (pin 4, J2). Pin 6 of J1 is used to reset the flip-flop.

When pin 5 of J1 goes high, the voltage across capacitor C5 will slowly fall. When this voltage reaches the threshold of inverter U2, the output will go high and the flip-flop will latch the value at "D" onto "Q".

Interface Configuration

In order to test this PC board, an interface fixture must be built. Often this interface can be a simple cable, or it may be a "bed-of-nails" type fixture. It depends on the mechanical configuration of the unit to be tested, as well as the extent of testing desired.

For this PC board, we will use a simple interface "box" that contains cables to plug into the board under test (since it has two connectors), and two pushbutton switches to allow control of the FT-100a test from the interface box. (START/STOP and WAIT/CONT).

The first step in setting up for a test is to define the desired input and output lines and how they are to be controlled or measured. Below is a diagram of the PC board connectors and the chosen I/O lines to connect to each. Note that there is a spring loaded test pin. This is to allow access to one point that does not go to either connector. The pin should be located such that it will contact the PC board on pin 3 of U3. A wire with a test clip or any other device that suits your particular needs could be used instead of a spring test pin. Also note that due to the somewhat limited I/O requirements, the entire test interface can be done using only one FT-100a I/O connector.

I/O INTERFACE DESCRIPTION
Unit under test		FT-100a
J1 PIN 1	-	+5 VOLT SUPPLY
J1 PIN 2	-	AA9 (analog input line)
J1 PIN 3	-	AA1 (analog output line)
J1 PIN 4	-	LA1:1 (digital output line)
J1 PIN 5	-	LA1:2 (digital output line)
J1 PIN 6	-	LA1:3 (digital output line)
J1 PIN 7	-	-12 VOLT SUPPLY
J1 PIN 8	-	+12 VOLT SUPPLY
J1 PIN 9	-	GROUND (DC and analog)

J2 PIN 1	-	AA10 (analog input line)
J2 PIN 2	-	LA1:4 (digital output line)
J2 PIN 3	-	LA6:2 (digital input line)
J2 PIN 4	-	LA6:3 (digital input line)
J2 PIN 5	-	LA6:4 (digital input line)

Test pin	-	LA6:1

Schematic of Interface

Now that the hardware is ready, all that's needed is a program to run the test. Below is a listing of a program with comments and explanations. There are usually many different ways of achieving similar results. This program is not proposed as an ultimate solution, but merely an example of one way to test the PC board. This program assumes that a serial printer is connected to the serial port and a hardcopy of the test results is desired.

Program Listing

BD_TEST      'Program Name
'
     CLS
'
'Initialize all I/O
     PA1=1
     AA1=0
     ER$="*** DEFECT *** "
'
'Print header information
     PRINT PRINT TAB 15; "************ FT-100a Board Test ************"
     PRINT " PC Board XYZ Run Number ______________"
     PRINT "Date: ";DATE$;TAB 20;"Time: ";TIME$
     PRINT
'
'See that all inputs are as expected
'
'Test analog inputs
     IF AA9 < 7.79 OR AA9 > 8.61 THEN CALL ER1
     IF AA8 < 4.5 OR AA8 > 5.5 THEN CALL ER2
'
'Test digital outputs
     IF LA6:1=1 THEN CALL ER3
     IF LA6:2=1 THEN CALL ER4
     IF LA6:3=1 THEN CALL ER5
     IF LA6:4=1 THEN CALL ER6
'
'Test relay contacts for open
     LA1:4=1: IF LA6:2=1 THEN CALL ER7
'
'Set variable resistor
     DISP "Turn R12 fully"       'Instruct operator
     DISP "Counterclockwise"
     DISP "Press CONT"
     DISP "when ready."
     WAIT                         'Set R12 & wait till done
'
     CLS: AA1=3.8                 'Set trip voltage
     DISP "Adjust R12 till"
     DISP "BEEP. If reach"
     DISP "end before beep,"
     DISP "press NO"              'Use external YES-NO pod
     LA1:4=1
'
L2: IF LA6:2=1 THEN BEEP: GOTO L1    'Wait for R12 to be adjusted
     IF NOT NO THEN GOTO L2             'Test NO pushbutton
'
     PRINT ER$; "R12 cannot be adjusted!"     'Defect in R12 adjustment
'
'Test LED circuit
L1: CALL LED: IF RESULT=1 THEN CALL ER8
     LA1:1=0: CALL LED: IF RESULT=0 THEN CALL ER8
'
'Test inverters and flip-flop
     LA1:1=1                       'Set "D" at flip-flop to 1
     LA1:3=1                      'Release RESET line on flipflop
     LA1:2=1                    'Initiate latch procedure
     DELAY 15                      'Wait 15 ms. for C5 to discharge
     IF LA6:1=0 THEN CALL ER9     'See if inverters switched
     IF LA6:3=0 THEN CALL ER10    'See if flip-flop switched
'
'Test Completed
     CLS: DISP "Remove board": DISP "Attach Printout"
     DISP "Connect Next": DISP "Board to test.";
     BEEP 5000,250
'
     FOR VAR1 = 1 TO 10: PRINT: NEXT   'Scroll printer paper 10 lines
'
     END
'
'
'-------- LED on/off test subroutine -------
' Operator has direct interaction with program through the YES-NO pod. ' If LED is on, YES is pressed, otherwise, NO is pressed.
'
LED: CLS: DISP "If LED is on,"
     DISP "press YES. If"
     DISP "off, press NO."
     RESULT=0
L3: IF YES THEN INC RESULT: RETURN        'YES pressed?
     IF NOT NO THEN GOTO L3                'NO?
     RETURN
'
'
'--- Error Subroutines ---
'
ER1: PRINT ER$; "Voltage at pin 2 of J1 = ";AA9;
     PRINT ". Should be between 7.79 - 8.61":RETURN
'
ER2: PRINT ER$; "Voltage at pin 1 of J2 = ";AA8;
     PRINT ". Should be above 4.5": RETURN
'
ER3: PRINT ER$; "Pin 4 of U2B is high with pin 1 of U2A low.": RETURN
'
ER4: PRINT ER$; "Pin 3 of J2 is high with open relay.": RETURN
'
ER5: PRINT ER$; "Pin 4 of J2 is high with flipflop RESET.";
     PRINT " (Pin 6 of J1 = 0)": RETURN
'
ER6: PRINT ER$; "Pin 5 of J2 is high.";
     PRINT " Should always be low (Ground line).": RETURN
'
ER7: PRINT ER$; "Relay contacts are shorted.";
     PRINT " High on pin 2 of J2 produces"
     PRINT TAB 15;"high on pin 3 of J3 (with relay open).": RETURN
'
ER8: PRINT ER$; "LED is not switching properly.": RETURN
'
ER9: PRINT ER$; "U2 A & B are not switching properly.": RETURN
'
ER10: PRINT ER$; "Flip-flop U3 not latching properly.": RETURN
'
/

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Programming Examples

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With limited exposure to the FT-100a programming environment, the examples might seem unclear and overwhelming, but the intent is to demonstrate the simplicity of the FT-100a programming language. All programming commands are covered in detail in the FT-100a Operator's Manual.

Schematic of PC board under test