pic 16f877a program problem

Are you saying you want to microcontroller to read a value that is displayed on a 3 digit 7-segment display?

Bob

 

LOL

Go Bob! Go Bob! Which microcontroller are you going to use?

shrinivasdevkar, can you answer some basic questions.

What is driving the displays?

What is the product? Some kind of counter?

What supply voltages are available?

Have you done microcontroller development before? If so, which device(s) did you use?

 

OK, that's useful information.

It should be possible to do what you want, but there is some hardware and software work required.

That multiple-digit LED display must be driven using multiplexing. If you don't know what that is, Google multiplexed led display drive.

To read the contents of that display, you will need to monitor the eight outputs that drive the segments, and the three outputs that select the digits. (It's possible that the digit selection is done with a 2-bit binary control signal and a decoder, but more likely there are three separate control lines.)

You need to find out how the display driver works, and where you can get access to those signals. Preferably they should be at 5V levels so you can feed them straight into your PIC microcontroller.

Then you need to write code in the PIC to detect when each digit is enabled, read the segment enable signals, decode them into a digit, then combine the three digits into a number that can be used for whatever you want to use it for.

Assuming you can get access to all of the signals at logic levels (so you can connect them directly to the PIC inputs), you could build a fairly small board that might fit inside the meter's case. It would need 13 connections to the meter board:

8x segment enable signals;
3x digit enable signals;
VCC and 0V.

Can you take a photo of the inside of the meter? Both sides of the board would be good. Make sure that IC markings are readable. If necessary, move the display so we can see what's behind it.

Do you understand what I've described so far?

 

When you measure voltage across segments in the display, you will not see 5V for several reasons. First, the forward voltage of a single red LED is around 2V (if the segment is powered from 5V, the remaining 3V is dropped across the current limiting resistor). Second, each digit is only enabled for 1/3 of the time.

You should not measure the voltage across the segments. This will not give a useful result, because of the multiplexing. Do you understand multiplexing?

The device (probably a microcontroller) that drives the 3-digit display will have a number of output signals that are probably all logic-level signals. You can connect these directly to your PIC. You should not need any op-amps or comparators. You just need to figure out where all the signals are.

I need to see both sides of all of the circuit boards inside the TC303AX. They need to be in focus, and all the component markings need to be readable.

 

It will be simpler to connect to the logic-level signals (0V/5V) which drive the anodes and cathodes of the display. If you do that, you won't need any op-amps or comparators. Yes you will need to connect the 0V rail of the TC303AX to the 0V rail of your PIC circuit. You may also be able to use the TC303AX's +5V power supply for the PIC.

Do you understand multiplexing?

 

OK, I will help with the program once you have worked out where to get the segment and digit control signals on the boards inside the TC303AX and drawn up a schematic diagram of your PIC circuit.

Do you know where to get those signals? If not, I will help you find out. I need to see both sides of all of the circuit boards inside the TC303AX. They need to be in focus, and all the component markings need to be readable.

Do you understand multiplexing?

 

I don't have one.

Are you asking me to write your code for you?

Post photos of both sides of all of the circuit boards inside the TC303AX. They need to be in focus, and all the component markings need to be readable.

Do you understand multiplexing?