Re: IR sensor with LM324


Manimozhi Baskaran wrote:
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 | | >--. | | >-----+-+--|| | |
-------|-----|-/ `-|<--|---+--|-/ | | piezo(5V-9V) | |
| |/| 1N914 | | |/ | +| | |
| | 100K +----[100K]-' | | |
| 1/4| | | | | |
100K 324| | === 0.2uF (B) | | |
| | | | | | |
-----+-------+----------+---+----------------+--------------------------------------------- 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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