CD4511 Decoder Schematic Help!

[BocajDude]

Hi I'm working on a relay clock and I've run into a small problem. I'm trying to read the data sheet for the CD4511 decoders I bought (with my limited understanding of electronics), and am not fully understanding the use of the circled resistors (10k Ohm). I already bought a set of 10kΩ resistors, but knowing their purpose will help me down the road. Many thanks!

 

[Harald Kapp]

Welcome to EP.

These are pull-down transistors, required to ensure logic low at the inputs of the gate when the switches are open.

Regards,
Harald

 

[dorke]

Hi I'm working on a relay clock and I've run into a small problem. I'm trying to read the data sheet for the CD4511 decoders I bought (with my limited understanding of electronics), and am not fully understanding the use of the circled resistors (10k Ohm). I already bought a set of 10kΩ resistors, but knowing their purpose will help me down the road. Many thanks!

Like Harald said,
they are pull-down resistors.
But you don't need them in all cases, actually mostly you don't

If you need more help with your clock,do share the schematics...
I can guaranty(!) it will be worthwhile

 

[BocajDude]

Of course!! I should have known. Thanks for the fast reply! I'll gladly share my schematics soon.

 

[Harald Kapp]

But you don't need them in all cases, actually mostly you don't

Actually, in cases as shown in the schematic you do need them.
The cases where you don't need them are whenever a driving gate is connected.

A long time ago, when TTL (74xx) parts were common, you could leave unused inputs open and the gates recognized these as logic High. This changed with the advent of CMOS technology. CMOS inputs are high impedance. Left floating (unconnected), a voltage anywhere between 0 V and Vcc can develop on the input, bringing the input stage into the linear region with all the adverse side effects (high currrent consumption, latch-up etc.)