Electrical – Seven Segment display output problem

display

I am trying to come up with a circuit using logic gates to drive a seven segment display.

I have a circuit with a BCD output (A, B, C, D) and need to convert this so that when any one of nine buttons are pushed, they produce a number.

The circuit needs to display a 0 when nothing is pressed. However, when buttons 1 – 9 are presesed it needs to display 7, 4, 8, 0, 5, 6, 8, 8, 9, respectively.

I have produced truth tables and k-maps, which all seem to be correct. But, it does not seem to be working at all. I get random numbers and a couple of odd displays of random elements on the display (not numbers or letters).

If anyone can point me in the right direction, or give me some advice, I would be eternally grateful!

Best Answer

It's not clear why you're going via BCD. Just create the combinational logic directly.

schematic

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Pressing a switch turns on the segments connected by small signal diodes.

Related Solutions

Electronic – arduino and seven segment with two digit

Guessing about what the problem is you're facing as you don't give enough details.

int val = 0;
val = analogRead(analogPin);    // read the input pin
int temp= val*5 ; //calculating the voltage
temp /= 1024 ;    //calculating the voltage
temp = (temp) * 100 ;// as 1V/100c

You are using integer math, for Arduino this means both val and temp are whole numbers ranging from -32768 to +32767.

You read a value from ADC, this value ranges from 0-1023 and you did not set the reference voltage. This means that reading 0 equals GND / 0V and reading 1023 equals +Vdd = 5V (approx. varying with your power supply, possibly being USB).

Say your supply voltage is 5V and the voltage at the input pin is 0.7V. The analogRead(analogPin); will return 1024 × 0.7 / 5 = 143.

Next you multiply that number: 143 × 5 = 715, so far so good.

Then you divide this number by 1024, this is where your program goes wrong: 715 / 1024 = 0.689 but we are doing integer math, and integers hold whole numbers only and all numbers after the decimal point will be chopped off! So temp is 0 at this point. It doesn't matter how much you multiply the result from this point, it will always be 0.

Change int temp to float temp, that should solve your issue. It instructs the compiler not to use integers, but to use a floating number instead.

There is an error here too:

int tempL; //low number
tempL=int(temp*10);
int tempH;//high number
tempH=int(temp/10);

Change it to:

int tempH;//high number
tempH=int(temp/10);
int tempL; //low number
tempL=int(temp-tempH*10);

Electronic – arduino – Segment display – Why selecting segment by GND

This is quite normal. Segment displays like that are usually available in both common anode and common cathode types. What you originally had was a common cathode type. What you have now is a common anode type.

Segment display

Common anode displays are sometimes preferred because you can easily drive them with a darlington driver array, like the ULN2803:

ULN2803 driving common anode LEDs

The ULN2803 can sink quite a lot more current than a microcontroller GPIO pin, and so drive large, high brightness displays.

Best Answer

Related Solutions

Electronic – arduino and seven segment with two digit

Electronic – arduino – Segment display – Why selecting segment by GND

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