MOBILE HOME Technical Tips


The display is a fast switching squarewave, on CRT display the vertical traces are hardly visible so the visible dotes are the horizontal traces. Each dot of the display is a trace of 20 uS. The voltage level for the dot is generated by the Vref generator which is part of the PIC16F628. PIC asm and C code, and a circuit diagram are included.
The counter time base is 1 second. During 1 second count the display is on, it goes off for the duration of the conversion from binary to decimal. The C version uses the compiler method of converting binary to decimal and the conversion time is about 0.5 second. In my assembler version the conversion requires 10 instructions for each bit hence 10 seconds for 1 MHz.
Set the oscilloscope time base to 1mS/div. Connecting the Trigger is optional but very useful. Set the scope input to 50mV/div. The signal level depends on the resistor connected across the output of the PIC, see circuit diagram. The purpose of the resistor is to compensate for low quality probe, with good probe the resistor can be removed and setting the scope input to 1V/div.
For the method of displaying text on oscilloscope screen I was mostly influenced by Emilio Pietro's project:
Software includes PIC code (6KB). You are free to use the circuit diagram and the software with no limitations.

Circuit Description
See also Technical Tips

5V is the supply to the microcontroller.

Pin 12 is the frequency input, input signal has to be TTL type (for 5V supply).
Pin 11 is a trigger signal for the oscilloscope. If your scope has a good internal trigger then you can do without it.
The 3K3 resistor is to compensate for low quality probe, with good probe the resistor can be removed or increased to 10K. The output signal level depends on the value of the resistor.
The other pins are not in use but must be left open circuit.


Comments and questions

Copy the number from the picture It stops net-robots from adding comments.

03.09.2016 - 22:14
Name: kris_from Cheshire England
Comment: Great little circuit - built one and fitted it to a probe style case all works - thank you for putting this up Regards kris - and happy building.

30.05.2015 - 23:29

16.01.2013 - 16:58
Name: tohu