Juma TRX-2 V.4.00a Build 6

[5B4AIY]

Build 6 - 11/JAN/2018
This build optimises the Vibroplex contact bounce suppression logic by eliminating a redundant test, and ensuring that the contact bounce suppression timer is only set once on the initial contact closure detection.

This version makes no EEPROM changes, and so can be safely loaded over the previous version. As with all firmware updates, it is a wise precaution to make a note of your calibration and configuration settings prior to loading the new version.

Build 5 - 28/DEC/2017
Some time ago I acquired a rather scruffy 43 year-old Vibroplex 'Presentation' bug key, and I have now refurbished it. When I connected it to my TRX-2 with the CW Keyer set to the STRAIGHT mode, I found that despite careful adjustment, I was getting 'scratchy' dots.

As the attached oscilloscope screenshot shows, this is caused by significant contact bounce on initial contact closure. Indeed, knowing how this mechanical semi-automatic key works, it would be somewhat surprising if there were no contact bounces. When these keys were originally produced they keyed vacuum tube equipment, and the time constants of their keying circuitry was such as to ignore contact bounces.

Unfortunately, solid-state equipment has a very much faster response rate such that in this case the keying logic was well able to follow the rapid state changes, resulting in scratchy sounding dots. As the keyer logic is embedded in the main timer interrupt code, it is essential to avoid delays, and thus another method had to be found to eliminate this nuisance.

The screenshot shows that the contact bounce interval is about 5mSec, and so a timer was added that is set to 10mSec at the first detection of a contact closure. This timer is decremented by the timer interrupt, and effectively causes the logic to ignore any further state changes until it is reset. This modification has no effect on the maximum keying speed, and has completely eliminated the scratchy dots problem.

As there are no EEPROM changes, this version can be safely loaded over the previous version. As with all firmware updates, it is always a wise precaution to make a note of your existing calibration and configuration settings prior to loading a new version.

73, Adrian, 5B4AIY