I have a temperature circuit that uses a common anode seven segment four digit temperature display.

It uses a PIC12F1572 to read the temperature from a one wire device and shift the numerical bits to a TLC5917 LED driver (shift register) to display the 0-9 on each of the four digits. This chip sinks each of the LED segments so the cathode is connected to each of the ports.

Daisy chained off the TLC5917 is 74HC595 shift register. Its job is to control which digit is lit during the multiplex process. I only use 4 ports for the four digits which connects the common anodes of the display. While this works I am concerned that I am drawing too much current from the 74HC5959 so I added transistors to turn the digits on and off.

Here is my question / confusion:

I had to use a 3904 NPN with the emitter connected to ground and the collector connected to the anode of the appropriate digit. This is not how I learned to use BJTs, and it seems wrong. Am I missing something, did I make a mistake or is the correct? What ever the response is, why?

This circuit works as desired and is exactly what I wanted to achieve.

I have also attached a schematic to better illustrate the circuit.

Images of each section for better visibility. Feedback is welcome, thank you.

I have a temperature circuit that uses a common anode seven segment four digit temperature display.

It uses a PIC12F1572 to read the temperature from a one wire device and shift the numerical bits to a TLC5917 LED driver (shift register) to display the 0-9 on each of the four digits. This chip sinks each of the LED segments so the cathode is connected to each of the ports.

Daisy-chained off the TLC5917 is 74HC595 shift register. Its job is to control which digit is lit during the multiplex process. I only use 4 ports for the four digits which connects the common anodes of the display. While this works I am concerned that I am drawing too much current from the 74HC5959 so I added transistors to turn the digits on and off.

Here is my question / confusion:

I had to use a 3904 NPN with the emitter connected to ground and the collector connected to the anode of the appropriate digit. This is not how I learned to use BJTs, and it seems wrong. Am I missing something, did I make a mistake or is the correct? Whatever the response is, why?

This circuit works as desired and is exactly what I wanted to achieve.

I have also attached a schematic to better illustrate the circuit.

Images of each section for better visibility. Feedback is welcome, thank you.

I have a temperature circuit that uses a common anode seven segment four digit temperature display.

It uses a PIC12F1572 to read the temperature from a one wire device and shift the numerical bits to a TLC5917 LED driver (shift register) to display the 0-9 on each of the four digits. This chip sinks each of the LED segments so the cathode is connected to each of the ports.

Daisy chained off the TLC5917 is 74HC595 shift register. Its job is to control which digit is lit during the multiplex process. I only use 4 ports for the four digits which connects the common anodes of the display. While this works I am concerned that I am drawing too much current from the 74HC5959 so I added transistors to turn the digits on and off.

Here is my question / confusion:

I had to use a 3904 NPN with the emitter connected to ground and the collector connected to the anode of the appropriate digit. This is not how I learned to use BJTs, and it seems wrong. Am I missing something, did I make a mistake or is the correct? What ever the response is, why?

This circuit works as desired and is exactly what I wanted to achieve.

I have also attached a schematic to better illustrate the circuit.

I have a temperature circuit that uses a common anode seven segment four digit temperature display.

It uses a PIC12F1572 to read the temperature from a one wire device and shift the numerical bits to a TLC5917 LED driver (shift register) to display the 0-9 on each of the four digits. This chip sinks each of the LED segments so the cathode is connected to each of the ports.

Daisy chained off the TLC5917 is 74HC595 shift register. Its job is to control which digit is lit during the multiplex process. I only use 4 ports for the four digits which connects the common anodes of the display. While this works I am concerned that I am drawing too much current from the 74HC5959 so I added transistors to turn the digits on and off.

Here is my question / confusion:

I had to use a 3904 NPN with the emitter connected to ground and the collector connected to the anode of the appropriate digit. This is not how I learned to use BJTs, and it seems wrong. Am I missing something, did I make a mistake or is the correct? What ever the response is, why?

This circuit works as desired and is exactly what I wanted to achieve.

I have also attached a schematic to better illustrate the circuit.

Images of each section for better visibility. Feedback is welcome, thank you.

I have a temprature circuit that uses a common Anode 7 segment 4 digit display temperature.

A PIC12F1572 to read the temperature from a one wire device and shift he numerical bits to a TLC5917 LED Driver (shift Register) to display the 0-9 on each of the 4 digits. This chip sinks each of the LED segments so the cathode is connected to each of the ports.

Daisy chained off the TLC5917 is 74HC595 shift register. Its job is to control which digit is lit during the multiplex process. I only use 4 ports for the four digits which connects the Common Anodes of the display. While this works I am concerned that I am drawing too much current from the 74HC5959 so I added a transistors to with the digits on and off.

Here is my question / confusion I had to use a 3904 NPN with the Emitter connected to ground and the collector connected to the Anode of the appropriate digit. This is not how I learned to use BJT and seems wrong. Am I missing something, did I make a mistake or is the correct. What ever the response is why?

This circuit works as desired and is exactly what I wanted to achieve.

I have also attached a schematic to better illustrate the circuit.

Thanks

I have a temperature circuit that uses a common anode seven segment four digit temperature display.

It uses a PIC12F1572 to read the temperature from a one wire device and shift the numerical bits to a TLC5917 LED driver (shift register) to display the 0-9 on each of the four digits. This chip sinks each of the LED segments so the cathode is connected to each of the ports.

Daisy chained off the TLC5917 is 74HC595 shift register. Its job is to control which digit is lit during the multiplex process. I only use 4 ports for the four digits which connects the common anodes of the display. While this works I am concerned that I am drawing too much current from the 74HC5959 so I added transistors to turn the digits on and off.

Here is my question / confusion:

I had to use a 3904 NPN with the emitter connected to ground and the collector connected to the anode of the appropriate digit. This is not how I learned to use BJTs, and it seems wrong. Am I missing something, did I make a mistake or is the correct? What ever the response is, why?

This circuit works as desired and is exactly what I wanted to achieve.

I have also attached a schematic to better illustrate the circuit.