Hi Everyone,

I am in the process of designing a scoreboard for my cricket club. We will need to display runs scored (3 digits), wickets (1 digit) and overs (2 digits).

So far I have made a single digit prototype using a BCD thumbwheel switch to input to a CD4543 IC which drives a 0.5" 7 segment display. I have used 470R resistors on the outputs to the led segments. This works fine with an 8V supply. My next step was to substitute the 0.5" display for a 5" (125mm) display from futurlec. I have increased the supply to 15.75V and this works, but the display is very dim and only passing 0.33mA per segment. The data sheet for the display gives Vf 9.25, If 20mA. By my calculations this should give me a resistor value to use of 275R. By using 2 x 470R resistors in parallel, giving me 235R I still only get 0.38mA. Obviously I am doing something wrong here and would appreciate any help.

Many Thanks in advance,

Mike

 

The CD4543 isn't powerful enough to drive the huge display.

You need to use some transistors to buffer the output so it gan drive the display.

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Ok thanks I will try that.

Regards

Mike

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OK Latest update.

I have found that using a 30V supply using 580R resistor will drive the display segment at 23mA, giving excellent brightness. I have a PSU from a HP printer which gives 15-0-30 output. I can drive the 4543 with the 15V side. If I take the outputs (high) from the 4543 straight into the inputs of a ULN2004A, can I take the 30V to the common anode of the 7 segment and the outputs of the ULN2004A to the relevant cathodes?

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It should work fine. There is no need to connect pin 9(common) of the
ULN2004A as those it is used when driving a relay or a small motor.

I have a homade digital clock that uses 6" displays and I used the ULN2004A's to drive my large displays.

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