Music Bell with In / Out Indicator

Here is a simple Music Bell with  In and Out indicator. The bell as well as the display turns on for 2 minutes and stop automatically. The circuit uses the popular ROM IC UM66 to generate music tone and a common cathode 7 segment display to show In or Out.

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2 responses to “Music Bell with In / Out Indicator

  1. Dear Sir…..
    IC UM66 has only three pin outs………but in your circuit a 220K resistor is connected in between the 7 and 8………please explain it….