Changing the processor allows you to play with the control code of the kit and add extra features, as well greatly adding to your knowledge of microprocessor control techniques

Programming a Picaxe chip is a remarkably simple process, and uses the 3 programming pins provided next to the microprocessor socket, which are not used if the preprogrammed 16F873A is fitted

The code for the PICAXE 28X2 is in simple BASIC format and has been prepared using the "Programme Editor 5" from Revolution Education. This simple to drive FREE piece of software will program and modify the code in any PICAXE chip. and is either known as the "Programming Editor 5 " or Picaxe Editor 6.1 depending on the version

Use the following link to get it........Revolution Education

Now change your crystal from 20MHz to 16MHz. Any crystal will do, as the displayed frequency can be adjusted to read correctly using sofware changes shown below.

Next, you must interconnect your computer to the analyser and a cable is required. There are two ways to do this, either with a 3 wire cable from your COM1 serial port (details below), or via a USB connection. It is firmly recommended that a standard serial port is used to load the Picaxe chip. If you must travel the unreliable USB route,then make sure that you buy the programming cable from Revolution Education, or at least purchase a conversion cable with a genuine FTDI chipset. Many (most) USB to serial cables on the market use counterfeit Chinese chipsets which do not fully implement the conversion between USB and serial standards, and/or have dodgy driver software.You will consequently find that you are in more trouble than can be believed!!

Another and probably cheaper way than USB is to buy a genuine serial card for your desktop.

  • Details of the cable to download program data from a serial port to the Picaxe 28X2

    The next step is to download the BASIC code for the Picaxe28X2 from this link, and copy and paste it into a text editor (Notepad or similar) giving it the name "9018Code.bas"

  • BASIC Code for the Picaxe 28X2 processor

    Interconnect your computer with the Analyser using your chosen cable and also connect a 12 volt dc supply to the analser main pcb, but do not switch on yet. Open the "Programming Editor" and select the 28X2 processor. Load the Picaxe code file into the "Programming Editor" and switch on the 12VDC supply to the analyser. Next click on "program" and watch as the code is squirted into the Picaxe. If all is well, the LCD should come alive, displaying figures. That's it!!

    Adding Your Call Sign Or Another Message At StartUp

    The following section of code will display your call sign or some other message at start up. It should be typed up in Notepad or a similar text editor.

    lookup b0,("VK5JST"),b1
    gosub wrchr
    if b0<6 then loop12
    pause 6000

    The message can be no longer than 16 characters (the LCD line length), and the number in the line "if b0<6 then loop12" must be equal to or greater than the number of characters in your message. So if your message was "Stolen from Jim" then this line would read "if b0<14 then loop12". Copy and paste this code into the downloaded file "9018Code.bas" directly after the section that dispays battery voltage at startup using the "Programming Editor". Then load the modified code into the analyser(see above). If all is OK, save the modified file.

    Eliminating The Tolerance Effects of The 16MHz Clock Crystal

    Almost any 16MHz crystal can be successfully used in the clock circuit of this analyser. To make the frequency displayed on the LCD read correctly, simply adjust the constants "8192" and 819 in the lines of the code shown below.

    count C.3,8192,w0 'Frequency counter routine. 5 digit resolution
    count C.3,819,w0 'Frequency counter routine. 4 digit resolution

    Modify these lines to be found in the code section "MEASURE AND DISPLAY FREQUENCY" using the "Programme Editor" and load the code into the Picaxe as previously detailed.

    Eliminating The Tolerance Effects Of The 5 Volt Regulator Output Voltage

    The onboard 5 volt regulator is used as the reference against which battery voltage is measured and has a +/- 5% tolerance To make the LCD display of battery voltage read correctly, open the file "9018Code.bas" in the "Programming Editor" and adjust the constant in the line w2=w2/100 below to somewhere between say 95 and 105. Load the code into the Picaxe as previously detailed.

    readadc A.3,b0 'External resistors are scaled to give a resulting
    'count of around 120 for a 12volt battery-33K from +12volt to
    'adc input 3 and 8K2 from adc input 3 to ground.
    w2=b0*100 'adjust the adc count by multiplication and then division so that
    w2=w2/100 'the display shows the correct voltage - change say division only
    w3=w2/100 'Derive individual digits for display