help with counters and decoders.

Thread Starter

PraveshKoirala

Joined Jan 25, 2012
5
First of all I am a beginner. And secondly, the circuit is not working. I've attached the schematic. The 7 segment display isn't being updated. Please tell me what's wrong there.
 

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bertus

Joined Apr 5, 2008
20,189
Hello,

There are several things wrong.
The 7447 CAN not work on 15 Volts, as it is TTL that is only allowed to work on 4.75 to 5.25 Volts.
Also there are no current limitting resistors for the display.
You think the display is not updated, but it is VERY fast updated (50 Hz), so fast you wont see it.

Also the control lines are not correctly set.
Have a look at the truth table of the chip:



Bertus
 
Last edited:

Thread Starter

PraveshKoirala

Joined Jan 25, 2012
5
Hello,

There are several things wrong.
The 7447 CAN not work on 15 Volts, as it is TTL that is only allowed to work on 4.75 to 5.25 Volts.
Also there are no current limitting resistors for the display.
You think the display is not updated, but it is VERY fast updated (50 Hz), so fast you wont see it.
Bertus
Hey,
I modified my schematic according to your solution. And it pretty much looks like this. But now the display refuses to light up at all. Can you plz have a look at it again?
EDIT:
The resistors are all 220 ohms
 

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MrChips

Joined Oct 2, 2009
19,778
What is the part number of your 7-segment display? You have to find out if your display is common anode or common cathode.

The 7447 decoder/driver is intended to be used with common anode displays.
For common anode displays, the common anode is connected to Vcc (+5V).

To test the display, temporarily connect pin-3 of the 7447 to GND.
 

bertus

Joined Apr 5, 2008
20,189
Hello,

The 7447 is a display driver that has open collector.
The driver is designed for Common Anode displays, connected to the 5V.
In your schematic you have a Common Cathode display.

Bertus
 
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