7 Segment display binary to decimal

Question

I have a few questions about 7-segment LED displays.

When we build a circuit using 7 segment (common-anode) and decoder (7447), we also use 4 tactile switches to make combinations. Should I directly connect switches to Vcc or ground (I have no knowledge about that) or what should I do with switches, after completing rest of circuit i.e. resistors to IC, IC to Vcc and display to Vcc?

I still need the answer but I think I did it!

Picture of my 7-segment display circuit

Answer 1

It is not recommended lo leave logic inputs floating. You should use a pull-down / pull-up resistor (see Spehro Pefhany's comment).

schematic

^{simulate this circuit – Schematic created using CircuitLab}

This circuit inputs low level by default (switch open). If you press the switch then it inputs high level.

schematic

^{simulate this circuit}

This circuit inputs high level by default (switch open). If you press the switch then it inputs low level.

• Gerben: In the first image it is actually called a pull-down resistor.
• Spehro 'speff' Pefhany: This is wrong. A 1K pull-up resistor should be used. 4.7K will not bring a TTL input into the region for a valid '0', since the input current is -1.6mA. A pull-down would have to be 250 ohms or less, and would waste a lot of power.
• Vitasset: So you say ı need to use 150 ohm resistor or something less than 470 ohm ?
• Spehro 'speff' Pefhany: @Vitasset Is "250 ohms or less" not clear? 240 ohms will work and is a standard E24 value. Two 470 in parallel will work. 150 ohms will dissipate 0.17W when the switch is closed, so don't use a 1/8" resistor, but it will work.