mystery of the flickering/poor contrast LCD displays ...

[no_self_control]

some time ago i commented on the way that the LCD displays on an aerospace avantage flickered in the window of an AD using neon strip lighting. also, many people have commented on the poor contrast of these displays. well, i think i may have an explanation.

i recently bought a couple of 988 movement parts for an early aerospace version. the PCB and the LCD. there is only an edge connector between these at the bottom, despite having top and bottom displays. i decided to try and count the number of contacts in the edge connector. about 30. it was then that i realised this wasn't enough to directly drive all the LCD segments as there are 7 per digit and about 60 in total. so, the segments are being driven by multiplexing. in other words, only being driven about half the time (2 x 30 = 60).

now this explains why there is a flicker as the segments that are active are only so half the time and consequently the light from the 50 Hz neon strip is interfering with the frequency of the display multiplexing as the segments are switch on and off.

now for a bit of a leap of faith and a possible reason for the poor contrast on the avantage compared to earlier aerospace versions. i think the number of connections has been reduced further and the amount of multiplexing has correspondingly increased, reducing the fraction of time the segments are driven (for example: 3 x 20 = 60 or 4 x 15 = 60). so the segments may in fact only be driven a third or a fourth of the time, instead of half the time, thereby reducing the contrast by a third or a half.

[rik]

my brain hurts! or should that be 'my brain hz'?! :-d

[SnapIT]

Interesting. I surmise that you would need a small 'LED' variable strobe to do a visual check of the display frequency. There is also one other consideration that civilians might not take into account when "comparing" the brightness of the LCD output to other brands and that is that the watch is nightvision compliant. This may well require a lower level of observable contrast to reduce the chance of "burning" the pilot's night vision within the cockpit environment. Something to consider.

[no_self_control]

Interesting. I surmise that you would need a small 'LED' variable strobe to do a visual check of the display frequency. There is also one other consideration that civilians might not take into account when "comparing" the brightness of the LCD output to other brands and that is that the watch is nightvision compliant. This may well require a lower level of observable contrast to reduce the chance of "burning" the pilot's night vision within the cockpit environment. Something to consider.

i've thought about the NGV compatibility and it doesn't make any sense as a reasonable explanation. if this were the issue, all that's needed is to reduce the brightness of the backlight, not the contrast, which affects visibility in both day and night conditions.

also, i have a replacement movement in my 'looks fake' breitling aerospace (the one with the CHR Ad and SP functions) that breitling UK assure me was sourced by them. this has the same poor contrast and no backlight facility. my suspicion is it's a cost reduced version that was also used in watches like the tissot titanium 7, of which i have one and it has the same functions and the same poor contrast. this replacement movement is link programable, which the 988 isn't, so it's obviously intended for more than one application.