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So I'm working on a 2 month design project with the following description enter image description here

I'm trying to exhaust the possible ways to design this without using microcontrollers or ready-made chips. Some of the problems I'm experiencing is:

  • How to turn on a buzzer after the counter reaches 99

  • How to alternately display the temperature and the count every ten seconds on the same set of LEDs

  • The count will simply come in the form of a high voltage of approximately 5 V.

  • The temperature will come in the form of a digital signal. I need only display on two 7-segment/8-segment displays.

  • A power of 5 volts for the counter IC is already given to me viz. 5 V.

I came up with the following block diagram so far just to give me an rough idea:

enter image description here

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  • \$\begingroup\$ Will people be allowed to leave during the counting period or does it only need to count occupants going in? Suppose you have 42 occupants and someone leaves, you would need to decrease the count to 41. Or is this like a roach hotel, they check in but the don't check out? \$\endgroup\$
    – GodJihyo
    Commented Feb 27, 2023 at 15:05
  • \$\begingroup\$ No. This very basic. It's just occupants entering. In fact, there will be an increment upon leaving as well. \$\endgroup\$
    – Zipho Lunika
    Commented Mar 1, 2023 at 19:27

2 Answers 2

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I added a few blocks to your block diagram to meet your requirements

enter image description here

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  • \$\begingroup\$ Shouldn't this have another comparator for the 40° temperature, and an or gate connecting both comparators and leading into the switch? \$\endgroup\$
    – Guntram Blohm
    Commented Feb 26, 2023 at 21:00
  • \$\begingroup\$ Yes indeed, I did not notice it in the question. I've updated the block diagram \$\endgroup\$
    – sai
    Commented Feb 27, 2023 at 6:12
  • \$\begingroup\$ (I'd add an alarm for occupancy < 0.) \$\endgroup\$
    – greybeard
    Commented Feb 27, 2023 at 8:33
  • \$\begingroup\$ That is not in the requirement \$\endgroup\$
    – sai
    Commented Feb 27, 2023 at 8:35
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The instructions say that the alarm should sound when maximum occupancy is exceeded, not when it reaches maximum. So you would need it to sound when the 100th person is added. If you use a counter IC with a carry out signal you can use that to trigger the alarm.

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  • \$\begingroup\$ I let @Zipho clarify the condition for sounding the alarm and update the block diagram accordingly \$\endgroup\$
    – sai
    Commented Feb 27, 2023 at 8:41

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