Help with a 3-digit display

[bogdy11]

Hello

Our project consists of the command of a 3-digit display with common cathode using 4000 series circuits and I need some help. We should use a 4093 (astable with trigger schmitt),a 4019 multiplexer (to select which tact to use,the internal from the astable or the external one),a 4029 decadic counter and a 4543 decodifier that commands a 7-segment common cathode diplay.

I have attached a pdf file containing the circuit's scheme.I would like you to look it over and tell me if it has something bad or if I didn't put a good dimension to some resistors or capacitors...

Thanx

Bogdan_rookie_electronist

 

[Souper man]

I use a 4511 when ever i use a 7 digit LED display, although i dont know what your requirement is.

 

[on1aag]

Hi Bogdy11,

I didn't check the entire circuit in every detail, I would need to check
all the datasheets and I'm far too lazy to do that. But I have two
remarks:

- What is the purpose of C2 & C3 ?

There's no need for debouncing in that part of the circuit !

- I don't understand the connection of D3 & R6 to the BI of the MC14513's.

The led D3 will never light unless you connect the BI of the MC14513's
to Vcc and I think that the MC14513's will blank their displays too.
Maybe you forgot to add a switch ?

Lazy on1aag.

 

[bogdy11]

About C2 and C3:

We were told that that's the only way that we can connect a switch to a circuit,with 2 resistors,2 capacitors(c2 and c3) and a SR latch.

About R6 and D3:

I know there's a problem with that LED and I know it won't light up...and that's why I need ur help.The fact is that we need a LED that can check the integrity of the display,so it should light up if one of the displays isn't working...I have no idea...Maybe we should but some sort of tact generator again...And also we should blank the unnecessary zeros.

About 4511:
We were kinda obliged to use the 4543 circuit...

Thanx for ur trouble......and please don't stop with the advise...

 

[ericgibbs]

hi bogdy,

Whats the voltage level on the BL blanking pin supposed to be, to enable the 4543 to drive the output pins.??

 

[bogdy11]

I suppose that the BI voltage level should be 1...5V...

 

[on1aag]

Hi Bogdy11,

The level on the BI of the MC14543's should be a logical "0" to
drive the display, a logical "1" will blank the display.
If you want to suppress leading zero's you have to detect if the
four inputs of the MSD are zero and apply the result to the BI of
the MSD. A four input NOR gate will do the trick.( Or a four input
OR gate plus an inverter.)
The same goes for the digit in the middle but you have to take
the result of the MSD in to the account as well.
The LSD does not require blanking, therefore the BI should be
connected to a logical "0".

on1aag.