Digital counter restarting at a exact number

I manage to do a digital counter with 3 displays that counts until 603 and then restarts and starts at 000, the thing is I have to make it so it restarts after 503, I managed to do it but then it starts at 200, I uploaded a picture of my project, in that picture it's made for 603 and it works fine, the only thing I change is I connect the second AND entry to Qa instead of Qb and there is when it doesn't work.

The schematic is poorly drawn and very difficult to follow.

1. Redraw the schematic with the three counter ICs in a row, with the most significant digit on the left and least significant on the right. Position each display above its counter. In this way, the displays read normally and it is much easier to follow the logic flow from one part to the next.

2. You have several unused inputs that are floating (not connected to anything). This will not work. Those inputs can change randomly due to electrical noise. Make sure all unused inputs are terminated correctly for the logic you are designing.

3. Add a reference designator to each component. Without them, it is impossible to discuss errors at specific IC pins. Use U1, U2, etc. for the ICs and X1, X2, etc. for the displays.

4. Use more direct wiring paths and eliminate unnecessary jogs, corners, and steps in the connection lines.

5. Never have a signal line cross over a component body.

6. Power symbols point upwards. Ground symbols point downwards.

To your specific question - you do not have enough gating to detect the reset value. Even with "lazy gating" you need at least 4 bit inputs, and your schematic shows only a single 2-input gate.

ak

I would add:

7. Do not run parallel lines close together. It makes it difficult to follow the signal flow.

8. Minimize the number of wire crossovers.

you need a presettable counter if you need it to start at a particular value. the counter you are using doesn't have a presettable register.

Disagree. He says the circuit always is to reset to 000, then start counting up again.

ak

AnalogKid said:

Disagree. He says the circuit always is to reset to 000, then start counting up again.

ak

Click to expand...

i must have read the OP wrong then, i thought he meant he wanted it to count from 503 to 603 and reset... a more careful reading of the question, he wants it to count to 503 and reset to 000, but it's resetting to 200 instead.