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multiplexed led display prob


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I want to build a counter with 7490's and a BCD to 7seg decoder(common anode). I don't want to use a microcontroller.
For control logic of switching transistors,I have used a 7490 and a 3:8 decoder which pulls base of PNP X'tors low sequentially.I wanted a logic that puts the correct BCD code onto the 7seg decoder when the correct LED digit is switched on.

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If you want to incorporate transistors with logic functions then you need a series resistor and a parallel resistors combination. I normally disregard the sink and leave it open. The source current should fall within the recommendation. You can bias the parallel combination to give you approximately zero volts. Otherwise it is your disgression to have whatever peak to peak you like. I hope this is a start.

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