7segmentdisplaybinaryswitches
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!
I do not believe you can reasonably run your display (or any multi-digit common anode display) using this chip. You may be able to finagle it to drive a single digit display through some creativity by hard-wiring the common anode to VCC and not connecting any of the DIG pins of the chip.
The way the chip works is that the SEG* pins "source current to the display" and the DIG* pins "sink current from the display common cathode". The way it's meant to be wired is that the common cathode of each digit on the 7SD is wired to a corresponding DIG pin and the SEG pins are wired to the corresponding anode segment pins of the 7SD. You serially load up "what should be displayed" into the memory of the chip and some configuration settings and it takes it from there.
The chip "scans" the 7-segment display for you and does this by, for each digit N:
There's just no way you are going to be able to take advantage of the chip's multiplexing algorithm because it relies on the DIG pins driving the common cathode to GND to "enable" each digit in turn.
You could insert an inverting buffer between all the SEG and DIG pins of the chip and the display and then you would communicate with the chip and wire it up "normally" as though it was a common cathode display. Not worth it if you ask me...
No, the 7660 is of no use. It can only supply enough current for a couple of segments, let alone displays.
The easiest (not necessarily the cheapest) way to get enough voltage for this display is to use a DC-DC converter, such as a TDK CC3-0512SF-E:
This one will output 12V at up to 250mA, so for a 3-digit display 10mA/segment is okay.
You will also need one resistor per segment of about 470 ohms, three ULN2003A darlington arrays.
If you have 9-12V available somewhere else, you won't need the DC-DC converter, but you will still need the resistors and the ULN2003As.
Best Answer
It is not recommended lo leave logic inputs floating. You should use a pull-down / pull-up resistor (see Spehro Pefhany's comment).
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.
simulate this circuit
This circuit inputs high level by default (switch open). If you press the switch then it inputs low level.