IR sensor with LM324

Feb 07, 2006 2 Replies
M

I built the circuit below with the IR sensor on the bread board A large bowl of snow was brought inside the house to the sense the snow Varied the 50 K pot (20 turns on the pot) No buzz output from sensor



Any suggestions on what is going wrong?



Thanks




---+-------+----------+----------- +5 -------- LM785 (NTE equivalent


one) (Vin) + 9V - |


| | | |
|
| | 100K | |
> | | | | |
> | | +-----[22K]-------+ | |
> 50K pot | | 1/4 | | |
> | |\\| | |\\ 324 | | |
> ref(A)+-----|+\\ +------|+\\ | | |
>IR in | | >--. | | >-----+-+--|| | |
> -------|-----|-/ `-| | |/| 1N914 | | |/ | +| | |
> | | 100K +----[100K]-' | | |
> | 1/4| | | | | |
> 100K 324| | === 0.2uF (B) | | |
> | | | | | | |
>

-----+-------+----------+---+----------------+--------------------------------------------- GND

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C

one) (Vin) + 9V - |

|

-----+-------+----------+---+----------------+--------------------------------------------- GND

Hi, Manimozhi. To start with:

1) Try just attaching the 9V supply to the piezo element. This won't kill it. But usually, beepers that have a specified DC voltage have the oscillator/driver built-in, and all you have to do is apply voltage. You might find your piezo element starts beeping when you apply DC voltage. If that's the case, the second op amp is doing exactly the wrong thing. But if you _do_ have a bare piezo element, you should be able to get much better results by bridging the drive with another 1/4 of the LM324.

2) According to your diagram, you have "IR in" as the inverting input of the first op amp. I'm assuming you've actually got a phototransistor or something like that. I'd like to know what it is, and also how you've got it hooked up. Many IR sensors require a pullup resistor to show a voltage. If you've got a meter, you can test this by just measuring the input to the op amp with the sensor in what should be the "on" and "off" states. It should change. If it's not changing, either something let the smoke out, you've hooked it up wrong, or some combination.

I'll tell you what. Answer those questions, and we can cobble together something that works for you, and put it in ASCII format for your safety and convenience.

What about the beeper -- does it beep with DC applied? What are you using for an IR sensor, and how do you have it hooked up?

Chris

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B

OK, I'll bite: Why would an IR sensor respond to a bowl of snow? Am I missing something here?

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Home of DaqGen, the FREEWARE signal generator

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