# circuits

Discussion in 'Homework Help' started by MilkyTank, Jul 27, 2012.

1. ### MilkyTank Thread Starter New Member

Jul 27, 2012
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0
PLEASE HELP i need to know how to decrement and increment 7segment using the 7447,74192 and LDR

2. ### MrChips Moderator

Oct 2, 2009
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You can begin by showing us your circuit that you are working on.

3. ### WBahn Moderator

Mar 31, 2012
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What is LDR?

While we can provide some hints and suggestions, a big part of the point of the problem is for YOU to figure it out yourself; it's the struggle from which you learn, more so than the end result.

4. ### MrChips Moderator

Oct 2, 2009
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LDR - light dependent resistor.
I assume the op wants to count objects going by.

5. ### MilkyTank Thread Starter New Member

Jul 27, 2012
13
0
this is the problem, i need to build a exit and entrance door and count the no. of people who enter the door at the same it decreases when somebody leave

this is my tools:

74192
7447
LDR
7segment

I dnt knw how to implement it

Apr 5, 2008
15,806
2,389
Hello,

Just have a look at the datasheets of the chips.
Then you can see what signals are needed.

If you want to determine the direction of the persons going in and out of the room,
you will need TWO ldr's and make a circuit that can see the direction.

Bertus

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• ###### dm74ls47.pdf
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Last edited: Jul 29, 2012
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7. ### MilkyTank Thread Starter New Member

Jul 27, 2012
13
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thanks!!!!! but im confused about the connection between the 74192 to 7447 i hope you can help me

Apr 5, 2008
15,806
2,389
Hello,

I have taken the pinout diagrams from the datasheets:

74192:

7447:

Bertus

Note: sometimes the pins are called different.
A can be called A0
B can be called A1
C can be called A2
D can be called A3

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• ###### 74192_pinout.png
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9. ### MrChips Moderator

Oct 2, 2009
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10. ### MilkyTank Thread Starter New Member

Jul 27, 2012
13
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how can i put out the buttons and change it to LDR

• ###### Capture.JPG
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Apr 5, 2008
15,806
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Hello,

Imagine a circuit that creates a puls on the up pin when a person walks along LDR 1 and then LDR 2.
Imagine a circuit that creates a puls on the down pin when a person walks along LDR 2 and then LDR 1.

What would be needed to create such a circuit?

Bertus

12. ### WBahn Moderator

Mar 31, 2012
18,091
4,917
What about when two people are passing the sensors at the same time in opposite directions? Virtually every combination, including missed and overlapping hits.

The OP said that he was supposed to have separate entrance and exit doors, so just use one LDR on each door. You have to assume that people come through one at a time and that you only get one interruption per person (not one for each arm plus one for the torse and maybe a leg thrown in).

[/QUOTE]

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13. ### MilkyTank Thread Starter New Member

Jul 27, 2012
13
0
can anyone give me some schematic about my problem. Im very confused iin how to do it

14. ### WBahn Moderator

Mar 31, 2012
18,091
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Have you tried building any of the circuits you've been directed to? Or the circuit that you yourself posted (which has some problems, but it's a start)?

Start by trying to just make a single digit count up or down in response to button presses. Once you have that working (and I suspect you are going to have some problems getting to that point), then it becomes much easier to do the rest.

So build just the one-digit version using buttons and tell us what happens when you try to use it.

15. ### MilkyTank Thread Starter New Member

Jul 27, 2012
13
0
i try to do it myself but it is not going smooth when it increase it always jump to far ex. 2 then 8 it always like that so that i try to see some other options

16. ### WBahn Moderator

Mar 31, 2012
18,091
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This is exactly what I expected you to see. I imagine that sometimes it jumps by, say, 5 and other times it jumps by, say 9.

Have you ever heard of switch bounce? Well, that's almost certainly what you are seeing.

So look up ways to debounce a switch. There are a few.

17. ### MilkyTank Thread Starter New Member

Jul 27, 2012
13
0
debounce switch?? like this??

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18. ### MrChips Moderator

Oct 2, 2009
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Debouncing an LDR is not the same thing as debouncing a mechanical switch.

The dual NAND-gate circuit is the classic way of using a single-pole double-throw switch or push-button.
(What you have there is an R-S flip-flop.)

Except that circuit is incorrect. Both R1 and R2 should be pull-ups (to Vcc). 10kΩ is suitable for CMOS gates. For 74LS00 TTL gates, R1 and R2 should be around 1kΩ to 4.7kΩ.

Debouncing an LDR sensor is a completely different story.

19. ### MilkyTank Thread Starter New Member

Jul 27, 2012
13
0
then how can i put LDR back to the line?? =_=

20. ### MrChips Moderator

Oct 2, 2009
12,648
3,458
The problem with the LDR is more about logistics than debouncing, as WBahn pointed out in post #12.

You can condition the signal from the LDR with a retriggerable monostable multivibrator such as a 74LS123 to produce an extended signal of a suitable duration.

The problem is that it does not identify the direction of motion.

Then there is the problem of two persons passing each other, one coming in and the other going out.

On a first iteration basis, you will need at minimum, two sets of sensors, staggered in position. One sensor will detect later than the other. From this you can determine direction.