Overview of the Functional Test Set

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Basic Description and Theory of Operation

The Functional Test System is a self contained LINUX based system designed to control and test most features of Digital PCBS running 8bit Microprocessors.

Embedded within the system is a Raspberry PI model 2/3 which handles the User interface such as the LCD display, keyboard and memory. It is preloaded with Custom Raspbian operating system and will function as any other Raspberry Pi would in that you can manage files, surf the web etc, etc.

Also embedded is an Arduino Mega 2560 which again is preloaded with a unique operating system A.O.S. This handles the hardware interface. Most of the front connector pins are linked to the Arduino and by instructing the Arduino with low level commands, they can be controlled in a manner which can simulate supported 8bit microprocessors. Other functions are available such as the A.D.T or future releases. Under most situations, the Test Program will handle all communications with the Arduino.

The Arduino also controls the dual LED displays and also handles the Active Probe input.

By linking the Raspberry Pi and the Arduino using software, the Function Test Set is created and will allow a variety of functions to be performed simply by clicking on screen buttons.

Limitations and Warnings

As with most testers, there are certain things which must be remembered when using them. This tester is no exception. Below is a list that should be read before any testing is performed and any connection is made to a UUT (Unit Under test).

. All connections (except the Active Probe) must not be allowed to go above 5V DC or less than 0V ref GND. . The Address Bus will normally be set to OUTPUT so make sure that when connecting to a UUT, the pins are not driven by another output. . The DC power connections on the front connectors are designed to provide power for external hardware and will not power full UUT,s. Current should be limited to 100mA only. . When running the A.D.T, false results can be given. This is due to the fact the test relies on an Active UUT and although a Snapshot is taken of the pins, the signals can be changing faster than the device responds. If such a result is given and the resultant truth table is considered wrong, retesting is recommended. If the device fails consistently on the same fault, then further investigation is required. Do not automatically assume the device is faulty until retested and checked. . Never allow more than 100VDC to enter the Active Probe input. Maximum is set to 99V. Also at the present time the probe will measure only POSITIVE voltages. . Do not allow any liquids or moisture to enter the tester and do not expose to excessive temperatures. . Above all, it has to be remembered that the tester is simply a tool although a complex one. As such it should be used in conjuction with existing knowledge and its results checked before suspecting a component is faulty. It will allow potential faults to be traced faster using its built in functions but as ever, further checks should be made before changing any parts. No responsibility can be held for damage caused by using the tester.

External Connections

On the front panel there are two connectors. Both are 25 way, female D-Types and are designated A and B. The connector to the left is A and the other B.

Front Connection

Connector A is Address and Data connections and supports 16 address pins labelled A0 to A15 and 8 Data pins labelled D0 to D7. The address pins are usually outputs but will revert to inputs on special situations. The data pins are BI directional and will change depending on the function required. An indicator on the LED displays will show the direction set.

Connector B is used for control and Auxiliary signals. On this connector, all the control lines for different processors can be found and also additional pins are used for 5V power and GND. There is an AUDIO input pin so signals can be routed direct to the on board amplifier plus pins allocated for future hardware and features.

Also on the front panel is a 50R BNC connection. This will accept a standard X1 scope probe and is a direct link to the Active probe circuit. It is protected to 100Vdc but care should always be exercised when using the probe function.

On the rear is an HDMI socket, Serial port for uploading new firmware and an audio/AV jack linked to the RPI.

Also is a green earth connection. This must be connected to the UUT under test as a reference level is required for the functions to work.

DC power is also applied on the rear panel and this should be 9V DC, 1A or better. Center pin POSITIVE

Rear Connection

The side of the tester has USB connections and a LAN connection although WIFI is built in and can be set up using the RPI screen.

Side Connection

Powering up and Shutting Down

To power up the tester, a DC mains adapter is required with center pin positive. The voltage should be between 6V and 9V DC and rated at approx 1.0A or better.

On the rear of the tester there is a DC socket which the adapter should be plugged into. Once plugged in, turn on the mains supply to the tester.

The LCD screen will turn white and remain like this for a short period of time before boot up info is displayed. If the External display has been selected previously, the LCD will go black after a short while with a cursor at the top left corner. The External display should be displaying the desktop at this point.

Once the Bootup is complete, the Main Desktop screen will be displayed as shown on next page.

Start Screen

Double Click the TEST icon to start the test program. Note this can be done either by using a mouse or by double tapping the LCD display if the external display is not enabled. Remember the LCD display is Touch Operated.

If all is well, the following display will be shown.

Test Screen

The LED displays will also power up and will initialise with the Version number of the software before settling down to display the Address (0000) and the data (--). The lower display will display a running dot indicating that the probe is active and the system is idle.

To turn off the tester or power it down, please do not simply pull the adapter plug out or turn power off as potential damage can be done to the system memory card.

To power down the tester by the correct means, Select the START menu by pressing either the WINDOWS key on the keyboard or clicking the lower left MENU button on the Desktop.

Select SHUTDOWN option from menu and then SHUTDOWN again. After a short while the LCD display will go white which indicates the power can now be safely removed.


Make sure no data is getting copied at the time as corrupt data might follow.

LED Display

The LED DISPLAY shows at all times the NEXT ADDRESS to use, any DATA and the Active Probe Values. Below is a picture showing the information displayed.

LED Display

Note that when in the Analogue Probe Mode, The Duty Cycle display will change to the voltage measured. This is displayed in volts and has two ranges.

The MODE indicator will be ‘d’ for DIGITAL probe and ‘A’ for ANALOGUE. When the probe is touched on a signal, the brightness will increase while signal is measured.

Backing up System files and data

As with most computer systems, taking a regular backup is always a good practice as corrupt data can strike at any time.

To back up the Testers files, there are two methods to use depending on whether it’s the system files or test data and programs.


This is done by using the Raspberry Pi built in commands. From the MENU on the Desktop, select ACCESSORIES then SD CARD Copier.

This will show a window which allows the complete operating system to be copied onto another memory card plugged into a USB connection on the tester. The Operating system is stored on a 16GB microSD card within the tester and if this fails, there is no other way to load it back. It is recommended therefore that a second 16GB microSD card is purchased and the System copied onto it as detailed above. If a failure occurs, it is then a simple case of replacing the card within the tester using the copied one. Note an entire copy is made including any user files etc.


The test files and user data are stored within folders located on the Desktop. Below is a list detailing the files contained.

/home/pi/Desktop/Devices - All data for the ADT is stored here

/home/pi/Desktop/ROMS - ID.crc file, all BIN files and TXT files

/home/pi/Desktop/TestProgs - All Test Sequences Generated.

/home/pi/Desktop - The TEST.desktop batch file

/home/pi/Test - Test Program

To copy any of the above, simply use the File Manager App and copy onto a USB card as usual. Information on using this can be found on the internet.

It is advisable and good practice to upload your files and add them to the resources section for others to benefit from your additions

Switching Displays

The tester can operate either the built in 3.5” LCD display or if preferred, an external monitor connected to the read HDMI connection.

To select which display is used, follow the instructions below.

Click the MENU button from the Desktop using either a mouse or the touch screen. From the options that appear, select the RUN option as shown below.

Screen Change #1 Screen Change #2

Next type in either one of the following command as required.

sudo ./lcd - Selects the LCD display

sudo ./hdmi - Selects the HDMI monitor

Note the command has to be exactly as shown above and in the picture on next page so sudo must be lowercase and followed by a space before the ./lcd or ./hdmi

Finally press ENTER or Click OK. The tester will reboot and afterwards, the selected monitor will be active. When using the external monitor, the TEST screen will be set to a smaller size. This is normal and cannot be changed. Also when other functions are selected, such as the ADT, these will appear as separate windows. Operate them as normal and always close them down when finished. Closing down the MAIN TEST SCREEN window will close the test program.