multiplexed led display prob

[shekhar_dandya]

Hi everyune,

I wanted to know that if we use a multiplexed Led display,how to implement control logic so that when 1st digit is activated by a x'tor,the code for first digit is through and so on.If microprocessor or microcontrollers are not used.

 

[leonsk1]

Tell what you need with more details, maybe I could help....

 

[shekhar_dandya]

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.

 

[Kevin Weddle]

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.

 

[shekhar_dandya]

Kevin,I did not get you.can you please elaborate it with a schematic?actually i wanted the logic between the BCD o/p's of decade counters and i/p of a 7seg decoder/driver.