FREQUENCY COUNTER FOR QRP WITH
ONE 7 SEGMENTS DISPLAY
 (1999)


Frequency counter with only one 7 segment display!
Really simple Barefoot Technology!

Frequency counter for simple and small sized QRP equipment
We are used to the frequency counter with a row of 5 or 6 displays. And these counters are not what we want for our simple QRP equipment. They need more components and space and draw more current than our QRP rig! But here is a perfect solution for this problem: The frequency counter with one 7 segments LED display! Well I can almost hear you think: THAT IS IMPOSSIBLE, but it is not! Indeed, one display is sufficient. The interesting part of this article is more the idea of how to display the frequency with only one display than the hardware.

How does it work
Very simple! The counter has a MHz / kHz switch. If we have for example a frequency of 14062.3 kHz then the frequency is displayed as follows:

Example for: 14062.3 kHz

The switch is in the MHz position: (coarse tuning)

.....off measuring..... 1 off 4 off 0 .....off measuring..... 1 off 4 off 0 .....off measuring.....

"1" is displayed for 250 milliseconds.
" " display is off for 80 milliseconds.
"4" is displayed for 250 milliseconds.
" " display is off for 80 milliseconds.
"0" is displayed for 250 milliseconds.
And after a 500 ms (or 1 s) display off period during the next frequency measurement, the "140" is displayed again.

The switch is in the kHz position: (normal operating, fine tuning position)

.....off measuring..... 6 off 2 off 3 .....off measuring..... 6 off 2 off 3 .....off measuring.....

"6" is displayed for 250 milliseconds.
" " display is off for 80 milliseconds.
"2" is displayed for 250 milliseconds.
" " display is off for 80 milliseconds.
"3" is displayed for 250 milliseconds.
And after a 500 ms (or 1 s) display off period during the next frequency measurement, the "623" is displayed again.


The frequency counter with one 7 segments LED display in a QRP transceiver!
Small size, low current and 100 Hz resolution!

Practical realisation of a one 7 segments display frequency counter

The design
The microcontroller AT90S1200 was selected for the job because I had a programming device for this RISC controller. This controller can count frequencies up to 6 MHz, so a 74HC4060 is used as /16 prescaler. During a 0.5 or 1 second period, the frequency is counted and then displayed via the 7 segments display in the way described here above.
There is also a 9600 baud RS232 connection for a PC. Via this connection, programming of frequency offsets and prescaler factor (power of 2) is possible.
The measured frequency is not only displayed, but is also sent to this RS232 port and can be displayed on your PC with a terminal program. It is also audible in CW via the internal beeper.


Circuit diagram
big diagram


Front view of the one display QRP frequency counter.


Side view of the one display QRP frequency counter.


Inside

Reading the frequency and programming of the counter via the RS232 port.


The Windows program for reading the frequency and programming of the counter via the RS232 port.
Set the date of your PC to 2003 if you want to try this trial version.

Programming the frequency offset and CW speed
This is done via the RS232 port (9600 baud, 8 bits). Connect D1 to ground to enter the program mode.
Type a question mark '?' and then the current prescale / offset is displayed on the screen.
When programming the counter, type it exactly as given here (Watch the capitals!).

'D0Pmmkkkh' + ENTER is a positive offset (F=VFO+IF) and a prescaler of 1x (power of 2 is 0).
Example: 'D0P090010' + ENTER is a positive offset for a 9.001 MHz IF (BFO) frequency for 14 MHz and a 5 to 5.5 MHz VFO.

'D4Mmmkkkh' is a negative offset (F=VFO-IF) and a prescaler of /16 (power of 2 is 4).
Example: 'D4M004550' + ENTER is a negative offset for a 455 kHz IF frequency for AM broadcast with the local oscillator of approximately 955 kHz to 2055 kHz.

'D1Rmmkkkh' is a VFO lower than the IF (F=IF-VFO) and a prescaler of /2 (power of 2 is 1).
Example: 'D2R090000' + ENTER is a VFO lower than a 9 MHz IF, for example a 9 MHz IF in combination with a 5 to 5.5 MHz VFO for 3.5 to 4.0 MHz and a prescaler of /2.

'Sa' is the CW speed. This is directly related to the ASCII value of a.
Example: 'Sd' is an ASCII character with value 100 (d=ASCII 100) and is approximately 12 WPM.

Software.

Download the CNT7SEG.ZIP (7k) file containing the CNT7SEG.ASM code for the AT90S1200.

Download the CNT7SEGEXE.ZIP (216k) file containing the Windows RS232 communications program. DOES NOT WORK ANYMORE...

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