IR shaft encoder

Thread Starter

h.d

Joined Oct 22, 2007
150
hi all
i implemented the follwing shaft encoder circuit
but the output voltage is very low(2V)
it should be around (4V)
i dont know what the problem.....anyone can tell me....?????
and thanks
 

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hgmjr

Joined Jan 28, 2005
9,029
The detector circuit is not an ideal one.

The first thing I notice is that the IR photodetector has no current flowing through it. This is due to the fact that the input current at the opamp is pretty close to zero.

Something quick you may try is placing a 1K feedback resistor between the output of the opamp and the negative input. Then adjust your potentiometer so see if you can bias the opamp's positive terminal to produce an output change when you expose it to the IR source.

hgmjr
 

Thread Starter

h.d

Joined Oct 22, 2007
150
when a touch the transmitter legs the output voltage increase to be 4V
i dont know if that means anything!!!!!:(
 

hgmjr

Joined Jan 28, 2005
9,029
It would appear from your schematic that you are using two IR emitters. Am I interpreting your schematic wrong?

hgmjr
 

hgmjr

Joined Jan 28, 2005
9,029
It would be helpful for you to post the part numbers of the IR emitter and the IR detector you are using so that we can consult the datasheet for each.

hgmjr
 

Thread Starter

h.d

Joined Oct 22, 2007
150
Not exactly sure what you mean by this statement. Can you clarify?

hgmjr
i mean that i use transmitter and reciever
and 2 transmitters
but its the same result...
i dont have serial numbers
its IR leds
 

hgmjr

Joined Jan 28, 2005
9,029
I visited the link you provided and I see the circuit you are using. The author is apparantly using the emitter to perform both the transmit and detect function.

I have not seen that implementation before.

hgmjr
 

hgmjr

Joined Jan 28, 2005
9,029
If you have digital camera or a cell phone camera you can use that to test the IR emitters to see if they are operating in the emitter mode.

hgmjr
 

Thread Starter

h.d

Joined Oct 22, 2007
150
ok i will try the camera, and wait the assistant from our forum members.
thanks for your time
 

hgmjr

Joined Jan 28, 2005
9,029
Assuming your IR LEDs are operating, you may have a problem with ambient light. Some conventional lights fixtures can emit a small amount of IR light. If you happen to be testing the circuit in an area that has some ambient IR light, the circuit may end up being triggered by this ambient IR light source. It may be worthwhile to test your circuit in a low light environment in case that is preventing your detector from working properly.

hgmjr
 

SgtWookie

Joined Jul 17, 2007
22,210
Looking at your receiver circuit:
1) Remove R5.
2) Remove the IR-sensitive diode, and replace it with a piece of wire.
3) Put the IR-sensitive diode where R5 was.

(See the attached)

You should now get at least some kind of response.

You are running the LM358 in open-loop gain mode. This is not recommended for operational amplifiers, because it means that the output will be constantly saturated, ie: maximum current dissipation. You should provide a feedback path, even if it's only a 100k resistor. This is shown as R4 in the attachment.
 

Attachments

Thread Starter

h.d

Joined Oct 22, 2007
150
Assuming your IR LEDs are operating, you may have a problem with ambient light. Some conventional lights fixtures can emit a small amount of IR light. If you happen to be testing the circuit in an area that has some ambient IR light, the circuit may end up being triggered by this ambient IR light source. It may be worthwhile to test your circuit in a low light environment in case that is preventing your detector from working properly.

hgmjr
i try it wi th and without ambient light......the same result us acheived.
i will exchange the IRLED's another time.
 

hgmjr

Joined Jan 28, 2005
9,029
Were you able to test the IRLEDs to confirm that they are illuminated when viewed using a ordinary digital camera or cellphone digital camera?

Be sure that the IRLED is powered in the correct polarity.

hgmjr
 
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