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I have designed a frequency counter circuit diagram. See below.

Now I am stuck on the part to wire up the decimal point in my circuit. The one that's the LED beside the 7 segment display. Do let me know if you find it hard to see the image below.

So basically I am supposed to:

Display the frequency on three 7-segment displays with a decimal point wired up so that:

  • The display is in the format XX.X.

  • If the current frequency is out of the current range, all the segments are OFF except for the decimal point.

  • Arrange the displays so they read left-to-right.

enter image description here

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    \$\begingroup\$ Is it always format XX.X? You have three range inputs determining which divider you count from, the decimal should reflect which if those is selected. \$\endgroup\$ – Phil G Mar 29 at 18:10
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1) If your display format is fixed at XX.X, there is no reason to have your range selection, so you can get rid of that.

2) You don't have an overflow detector. Use C13D output to freeze the clock input. Then gate that with the 555 pulse to reset IC1 and IC2.

3) You must use the 555 pulse to reset IC6 and IC8. This also means that the pulse must be narrower than the highest-frequency input period you expect to encounter.

4) Because you are using a ripple counter (IC6 & 8) you must expect the occasional weird reading, when IC1 and IC2 grab a count which has not fully propagated through your counter chain.

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Your schematic is cropped at the top so it's not clear what the pinout is.

Generally for a fixed point display the relevant digit's decimal point is wired permanently via a resistor to the opposite supply to the common pin.

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You are using open-collector drivers, so you should have series resistors on each segment line to limit the current and keep the brightness the same no matter how many segments are illuminated.

Use the same value resistor and connect the decimal point pin on the middle digit to ground through the resistor. Do not ground it directly or you will destroy the display.

You can use a bit higher value because the decimal point is smaller and it might appear too bright, but usually the same value is okay.

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