Get Help with Infrared Detection Circuit Design

In summary, the PIR sensor is expensive and not very effective without additional circuitry. The darlington transistor with high hFe is needed to get the correct current to power the solenoid (load). The required bypass capacitance for the sensor is listed on the data sheet (application circuit). The transistor's pull-down should go to ground.
  • #1
Wetmelon
154
1
Hey experts! I've designed an infrared detection circuit to drive a motor, but I need the circuit and my math checked. I tried 5Spice, but I can't get my head around it. Circuit image attached.

Do you know about how far I would be able to detect someone crossing in front of the light? I need 10-20 feet. Even farther would be great!

Edit: I should also mention that the TIP41C transistors are the correct components, but I am only using what Eagle had in its library for the other components, so they are not necessarily to spec.
 

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  • #2
Wetmelon said:
Hey experts! I've designed an infrared detection circuit to drive a motor, but I need the circuit and my math checked. I tried 5Spice, but I can't get my head around it. Circuit image attached.

Do you know about how far I would be able to detect someone crossing in front of the light? I need 10-20 feet. Even farther would be great!

Edit: I should also mention that the TIP41C transistors are the correct components, but I am only using what Eagle had in its library for the other components, so they are not necessarily to spec.

You're not really adding any gain to the IR Rx diode -- it would be better to use a photocurrent-to-voltage converter stage with an opamp. Also, for best real-world IR TX-->Rx performance, you should modulate the IR transmission and demodulate at the RX stage, to help reject DC IR and AC Mains (60Hz, 120Hz) interference.

You might be able to use Passive IR (PIR) sensing instead, if you are just looking for the motion of people / warm objects.
 
  • #3
Also, by modulating, you can typically drive the emitters at a higher current which can help increase the distance.

One of the closest real-world examples I could give you for the detection of an object detection 10-20Ft away would be the circuitry associated with the safety beam on a garage door system.

Edit:
I'm with Berkeman - PIR sensors for motion usually have a pretty solid performance. Just make sure you select the appropriate device with the correct lens (distance and detection area).
 
  • #4
Alright, so I decided that PIR was indeed the option most suitable for my application. I have revised my circuit to be compatible with the http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=255-2647-ND

However, this sensor is expensive! Does anybody know of a similar product that is quite a bit cheaper? xD
 

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  • #5
Wetmelon said:
Alright, so I decided that PIR was indeed the option most suitable for my application. I have revised my circuit to be compatible with the http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=255-2647-ND

However, this sensor is expensive! Does anybody know of a similar product that is quite a bit cheaper? xD

What is the function of Q1? Doesn't seem like it's needed anymore...
 
  • #6
berkeman said:
What is the function of Q1? Doesn't seem like it's needed anymore...

I don't want to burn out the switch. In my experience, most switches I've used only handle about .5A, which is just about how much my load draws, so it was iffy.

On the other hand, digikey search brings up small, cheap, effective slide switch that handles 6A @ 120VAC, (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CKN9891-ND), so I guess I don't really need it.

Edit: Updated diagram.
 

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  • #7
Some general notes:

1. At power-up, the output of the PIR is typically not stable, so your motor may run unexpectedly at first.

2. I'm pretty sure you will need some bypass capacitance to stabilize the output of the regulator. In addition, a bypass cap for the sensor wouldn't hurt.
 
  • #8
mdjensen22 said:
Some general notes:

1. At power-up, the output of the PIR is typically not stable, so your motor may run unexpectedly at first.

Yea, I was aware of this, and have corrected for it in the mechanical design rather than the electronic design. However, if there's an easy way to fix that in the electronics, I'd love to hear about it :)

2. I'm pretty sure you will need some bypass capacitance to stabilize the output of the regulator. In addition, a bypass cap for the sensor wouldn't hurt.

Added :) Any idea on the capacitor sizing I'll need?



The sensor only outputs 4.5 volts and .1mV, so I had to switch to a darlington transistor with high (10k) hFe to get appropriate current to power the solenoid (load).
 

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  • #9
The required bypass capacitance for the sensor is listed on the data sheet (application circuit).

The bypass capacitance for the regulator would be listed on its data sheet as well.

One other thing: the pull-down on the base of the transistor should go to ground. As it is drawn, (attached to the motor), its bias will vary between the motor on/motor off states.
 

1. What is an infrared detection circuit?

An infrared detection circuit is an electronic circuit that is designed to detect infrared radiation. It typically consists of an infrared sensor, amplifiers, filters, and other components that work together to detect and process the infrared signals.

2. How does an infrared detection circuit work?

An infrared detection circuit works by using an infrared sensor to detect the infrared radiation emitted by objects. The sensor converts the infrared signals into electrical signals, which are then amplified and filtered to remove any unwanted noise. The resulting signal is then processed and used to trigger an output, such as an alarm or a signal to a microcontroller.

3. What are the applications of an infrared detection circuit?

An infrared detection circuit has a wide range of applications, including motion detection, proximity sensing, temperature measurement, and remote control systems. It is also commonly used in security systems, automatic doors, and industrial automation.

4. What factors should be considered when designing an infrared detection circuit?

When designing an infrared detection circuit, several factors should be considered, including the type of infrared sensor, ambient conditions, noise sources, and power consumption. The circuit should also be designed to have a high sensitivity and a low false trigger rate.

5. Can an infrared detection circuit be customized for specific applications?

Yes, an infrared detection circuit can be customized for specific applications by selecting the appropriate components, adjusting the amplification and filtering parameters, and adding additional features, such as adjustable sensitivity or a time delay. It is important to carefully design and test the circuit to ensure it meets the specific requirements of the application.

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