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To get you going, you could just use your switches straight from VCC to the Anode (through current limiting resistor). With the emitter joined to VCC and the collector to your display Anode through a small resistor then current will flow from VCC through the PNP transistor to the display Anode. You could let the 74LS138 outputs drive a PNP transistor so that when it's output goes low it pulls current from the base (through a resistor, say 1K). The gure below shows a block diagram of a possible implementation of this controller. As your displays are Common Anode this is correct for the 74LS47, but the 74LS138 is incorrect, as you need to SOURCE current to the Anode of the displays. Our 4-digit seven-segment controller will take a clock and four characters (4-bit each) as inputs, and will write the seven-segment control signals as well as the four anode signals to display all four characters simultaneously. switch open = '1'.Ģ) Both of your driver ICs are of the type that SINK current, ie when the input in ON it looks like a swicth to GND.

Note, this ends up as opposite logi, ie switch closed = '0'. Multisim Live TM1650 Seven-Segment Display - Tasmota 4 Digit 7 Segment. Your switch then switched that input to ground. WebIn 7-segment displays, a common pin combines the anodes or cathodes of all LED. For TTL logic, you need to pull each input High to VCC with a 4K7 or similar resistor.

There are several problems with this circuit.ġ) Your switched don't connect to anything on one side so they cannot possibly do anything.