LM324 - IR Sensor

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 --------VoutLM785 (NTE equivalent one) (Vin) +9V- --------- |

 

I tried to clean up your diagram, which was not clear, and came up
with this:
------
---+-----+----------+--------- +5 ------Vout|LM7805|Vin--- +9V
| | | ------
| | | |
| | 100K |
| | | |
| | +-----[22K]-----+ |
pot 50K | | 1/4 | |
| |\| | |\ 324 | piezo |
ref(A)+---|+\ +------|+\ | 5V-9V |
IR in | | >--. | | >-----+-+--|| |
-------|---|-/ `-|<--|---+--|-/ | | |
| |/| 1N914 | | |/ | +| |
| | 100K +----[100K]-' | |
| | | | | |
100K | | === 0.2uF (B) | |
| | | | | |
-----+-----+----------+---+----------------+------+--- GND

Assuming the diagram is correct, your piezo is installed
backwards - you show the + going to ground.

Ed

 

---
With the 50k pot cranked to zero ohms the reference input to the
opamp will be 5V, and since:

E1R2
E2 = ------- ,
R1+R2

with the pot cranked to 50k the reference input will be:


E1R2 5V * 100kR
E2 = ------- = -------------- = 3.33V,
R1+R2 50kR * 100kR

So there's no way you can get to 0.8V, no matter how much you crank
the pot.

What you need to do is change this:

+----------+----+5V
| |
[50k]<-+ |
| | |
+----+----|+\
| | >--[<1N914]...
Vin>--|---------|-/
| |
[100k] |
| |
+----------+----GND


to this:


+----------+---+5V
| |
[100k] |
| |
+---------|+\
| | >--[<1N914]...
Vin>--|---------|-/
| |
[50k]<-+ |
| | |
+----+-----+---GND

which will get you your 0.8V point with the pot at adjusted to
about 19k ohms


Also, since you've got a slowly varying input signal it wouldn't
hurt to add a little hysteresis, like this:

+----------+---+5V
| |
[100k] +---|--[Rx]--+
| | | |
+------+--|+\ |
| | >------+--[<1N914]...
Vin>--|---------|-/
| |
[50k]<-+ |
| | |
+----+-----+---GND

if you can ever figure out what kind of accuracy you're looking for.