Problem with seven segement or 4511

Hi All,

I have this problem I have assembled the circuit for 1 second timer which is displayed on the 7 segment display using 4510 and 4511 and the frquency generated from the pulse generator. Now my problem is the 7 segment display displays 4,5,6,7,8 properly but 9,1,2,3 are displayed as 8 but if a stop the pulses after attaining 9 then after few seconds it displays 9 properly, similarly for other numbers 1,2,3. If I observe the 7 segment letters of the troubled letters, the voltages are falling slowly not instantly. Could somebody help on this? I have designed the board on the bread board, the problem is because of this?

Thanks in advance,
Regards,
Satya

Try to put pull-down resistor somewhere.

You should show us the shematic.

Check to see if the 4511 is designed for a common cathode or common anode (or possibly both) display, you might be using the wrong type of display for that chip.

Also make sure your current limit resistors are correct, you might be pulling to many milliamps from the decoder.

The 4511 decoder/driver is designed for common-cathode LED displays. (datasheet link here)

Hi All,

With your support I was able to solve the issue, as suggested I pull down to ground. Initially I was trying to pull down at the output of the 4511 but it was not working, then I pull down at the input of the 4511 (BCD inputs) then it worked.
Can anybody tell me why this pulling down is required? Does it mean that pins store some charge as capacitors?

Thanks in advance,
Regards,
Satya

You have to ground unused inputs, because if they float interference affects them.

A CMOS floating input has no defined state. Because of its very high impedance it can float to anywhere from 0V to the supply voltage. So you must tie all inputs to either a high or low voltage for proper circuit operation.

Hi All,

Frankly speaking the pins are not exactly floating, the pins are 4511 inputs and 4510 outputs (the counter outputs). So I connected directly from 4510 outputs to 4511 inputs without pulling them down. I am not able to post the schematic as I have not drawn the complete schematic.

Thanks and Regards,
Satya