[SOLVED] TTL 7447 to 7 Segment LED Problem

[mlbryant]

I am trying to set up a simple circuit using 4 SPDT Switches, a TTL 7447 BCD to 7 Segment Encoder, a common cathode 7 segment LED. I have added 4 green LED's to the circuit (one for each switch) for debugging purposes. The 4 green LED's light appropriately for the corresponding SPDT switch; however, non of the segments on the 7-segment will light up. I have tested each segment of the 7 segment with +5vcc through a 330 ohm resistor to each segment and the entire 7 segment LED works. I have also tested several 7447 chips, so I don't believe it is the chip either. I am enclosing a diagram of my circuit, as well as pictures of the circuit. In both the diagram and the pictures, switches 1 / 4 are flipped to +5vcc and switches 2 / 3 are flipped to ground.

 

[zuisti]

The 7447 outputs are active low so use a common anode 7 segment display (and put +5v to the common pin).

 

[mlbryant]

The 7447 outputs are active low so use a common anode 7 segment display (and put +5v to the common pin).

Grrr... I was afraid I had the wrong 7-Segment. This may be a silly, newbie question, but if the 7447 are active low, could I invert each of the 7 outputs from the 7447 through TTL 7404 and then send the those highs to the common cathode 7 segment?

 

[zuisti]

but if the 7447 are active low, could I invert each of the 7 outputs from the 7447 through TTL 7404 and then send the those highs to the common cathode 7 segment?

Yes, you can use 1+1/6 7404 to invert the outputs , but I think there are also 8bit inverting buffers ...

 

[mlbryant]

Thanks, that worked perfectly

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Thanks

This is the modified circuit diagram with one 7447, one common cathode 7-segment, and two 7404. Note the absence of the 330ohm resistors for the 7-segment LED because the output from the 7447 is 3.3v