Hi elec_mech.
Pin 3 & 8 of the display going to Vcc to half current makes sense. I've amended my drawing. However the C.A. displays only have 1 Vcc connection (connected to each segment) - so no problems.
The BCD in my timer schematic - correct, it was a mistake - built correctly, drawn incorrectly. I still need to rename components to numbers (i.e. R1, R2, C1, etc). Will do that soon.
View attachment Count down timer PCB_V6.pdf
PS. the BCD is still connected in the circuit to give full flexibility to change the count down time to something odd. I was looking at placing it somewhere water proof on the score board for people to access.
The blue syran wrap (we call cellophane) - will try it. Your absolutely right - I can imagine it will make a huge difference because the white of the displays won't be seen.
Higher voltage supply - yes, I will try it out.
Making my own digits if all else fails - yes, I tried already into perspex - cracks really easily. I did buy 100 leds of various colours and strengths already. I arranged some to make a digit and it worked, however my power supply couldn't handle it at the time. I even have 15000mcd leds - I'm "sure" they would be bright enough. It's just time to build. I see how I go.
As for the Vcc and current measurements (thanks for detailed explanation of how to measure), results are:
24.04 regulated power supply
Resistors = 7.5Ω
(C.A to segment / ULN to resis / ULN earth to ULN outputs / total Vcc)
a = 22.39v / 0.66v / 0.78v = 23.88
b = 22.36v / 0.68v / 0.78v = 23.82
c = 22.38v / 0.66v / 0.78v = 23.82
d = 21.68v / 1.27v / 0.76v = 23.81
e = 21.60v / 1.35v / 0.76v = 23.81
f = 22.50v / 0.60v / 0.78v = 23.88
g = 22.44v / 0.62v / 0.78v = 23.84
Average = 23.84.
Currents:
a=85mA, b=88mA, c=86mA, d=158mA, e=170mA, f=79mA, g=82mA.
Total = 748mA1 (Av 106mA).
Not sure why "d" and "e" go so bright. Obviously need larger resistors to compensate.
So from above, please correct me if I'm wrong:
a. Voltage supply of 24.04V "just covers it, but a bit higher would be safer
b. Adjust resistors with new supply to reach say 25mA per led (i.e. 25x5 per segment.
Pin 3 & 8 of the display going to Vcc to half current makes sense. I've amended my drawing. However the C.A. displays only have 1 Vcc connection (connected to each segment) - so no problems.
The BCD in my timer schematic - correct, it was a mistake - built correctly, drawn incorrectly. I still need to rename components to numbers (i.e. R1, R2, C1, etc). Will do that soon.
View attachment Count down timer PCB_V6.pdf
PS. the BCD is still connected in the circuit to give full flexibility to change the count down time to something odd. I was looking at placing it somewhere water proof on the score board for people to access.
The blue syran wrap (we call cellophane) - will try it. Your absolutely right - I can imagine it will make a huge difference because the white of the displays won't be seen.
Higher voltage supply - yes, I will try it out.
Making my own digits if all else fails - yes, I tried already into perspex - cracks really easily. I did buy 100 leds of various colours and strengths already. I arranged some to make a digit and it worked, however my power supply couldn't handle it at the time. I even have 15000mcd leds - I'm "sure" they would be bright enough. It's just time to build. I see how I go.
As for the Vcc and current measurements (thanks for detailed explanation of how to measure), results are:
24.04 regulated power supply
Resistors = 7.5Ω
(C.A to segment / ULN to resis / ULN earth to ULN outputs / total Vcc)
a = 22.39v / 0.66v / 0.78v = 23.88
b = 22.36v / 0.68v / 0.78v = 23.82
c = 22.38v / 0.66v / 0.78v = 23.82
d = 21.68v / 1.27v / 0.76v = 23.81
e = 21.60v / 1.35v / 0.76v = 23.81
f = 22.50v / 0.60v / 0.78v = 23.88
g = 22.44v / 0.62v / 0.78v = 23.84
Average = 23.84.
Currents:
a=85mA, b=88mA, c=86mA, d=158mA, e=170mA, f=79mA, g=82mA.
Total = 748mA1 (Av 106mA).
Not sure why "d" and "e" go so bright. Obviously need larger resistors to compensate.
So from above, please correct me if I'm wrong:
a. Voltage supply of 24.04V "just covers it, but a bit higher would be safer
b. Adjust resistors with new supply to reach say 25mA per led (i.e. 25x5 per segment.