Bascom and AVR, a TIL311 Bitx20 display
For my Bitx20 transceiver I wanted something 'different' as frequency display. I remembered I had a few
old Texas Instruments TIL311 hexadecimal led displays that seemed suitable. These displays first appeared in the
1970's, they use lots
of current (more than the BITX20 in receive...) but being led displays have excellent contrast.
Amazingly enough,
Texas Instruments
still has the
datasheet
online. Bravo TI!
I wrote a small
program
for the ATMega8 to read the BITX20 VFO frequency, add a constant IF frequency
and display the result. The VFO signal is buffered using a J310 and 2N3904. The buffer output
is connected to the T1 input of the ATMega8:
The program uses a constant to determine the count time (app. 100 milliseconds). If you use another chrystal frequency
you must change this value. Experiment!
The program then calculates the digits to display and sends these digits to the displays. The A, B, C and D
inputs of all display are connected together. The Latch Strobe inputs of all displays are connected to
Port C and D of the ATMega8. The program puts a digit to display on the ABCD pins and then toggles the relevant
latch strobe pin. The TIL311 displays have a digit memory, so you only need to write a digit if it changes. No
mulptiplexing is necessary! Although the schematic shows eight displays, I show the frequency as
You may want to omit the leftmost digit, or you can use a count time of one second to display all eight digits.
I considered a one second count time too long however. Using a 100 millisecond count time enables several display
updates per second and that is necessary when tuning accross the band. I also changed the fixed connection of the second
digit's decimal point to that of the third digit.
You can read more about using the counter features of AVR's in the
interrupts
chapter.
Curious to know what the Bitx20 is? Go to
Ashhar Farhan's
web. If you need more info, visit the
Yahoo Bitx20 group.
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