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At the end of this instructable you will be able to detect your car as it approaches the wall inside your garage, signalling you that the car is inside far enough so you can close the door.

Most car sensors will use a microprocessor to help calculate the distance of an approaching car when entering the garage. At our Wichita, KS makerspace MakeICT, we received a bag of components from JAMECO, which contain almost all the components needed to perform this instructable.

The main component and the challenge was to use a 555 timer as the driving "brains" of the project. So here we go:

 

Step 1: How Does It Work?

The theory of implementation is very simple. Avoid using an Arduino or any other type of microcontroller. Instead use a 555 Timer in astable (oscillating) mode such that it generates a 37.9kHz. We use the switching output of the 555 timer to drive an infrared (IR) Led. When we do this the LED will turn on and off at a rate of 37.9K time per second.

Why? So we can detect it with a special IR detector that will only sense IR light that is modulated (switched) at a frequency of 37.9KHz. Upon detecting the IR light at that frequency the sensor will drive its output line high.

IR light reflects off objects just light visible light do. So in our application as the car approaches the sensor, the IR light emitted by the 555 will bounce off the car and into the sensor. Just like in a pool table, the angle the light hits the object will make the light reflect at the same but opposite side. With this in mind we need to position the IR led and the IR receiver at an angle such that the car is detected only when the car is getting close to the wall, under other circumstances, the IR light will bounce off the car and never reach the sensor as shown below

Step 2: The Schematic

The schematic is easy to understand.

The 555 timer:
The main part here is the 555 timer in astable configurations. The 3 resistors to the right of the 555 timer (330, 22 and 680) control the charge and discharge of the 0.022uF capacitor which in turns generate the square wave at the output of the 555.

The 470 ohm resistor next going to the IR LED limits the current out of the 555 timer so we do not destroy it when driving the IR led

The 10K resistor ensures that the 555 is not in reset.

The IR Receiver
The IR receiver used was an erverlight IRM-8420 but just about any IR received for remote control applications would work. Since the IRM-8420 is only a 5V device a 78L05 regulator was used to ensure we power it correctly.

The IR receiver drives a Red LED when it detects a IR signal modulated at the 37.9kHz frequency rejecting all other IR light. That ensures that the sun light will not trigger the sensor.

The Power:
The power comes from a 9V square battery attached to the 5V regulator with some bypass capacitors. Those are all the ones I had handy but if you can add some more near the 555 timer and the IR receiver that would make it even better.

Step 3: Bill of Materials

In order to build a car detection circuit you will need the following components, since Jameco was so kind to provide our maker space with the parts, I figure I would use their part number off their website.

- Qty 1 555 Timer  
- Qty 1 10K Resistor 
- Qty 2 330 Resistor 
- Qty 1 470 Resistor
- Qty 1  22 Resistor
- Qty 1 680 Resistor

- Qty 1 0.022uF Capacitor 
- Qty 2 0.1uF Capacitor
- Qty 1 IR Led 
- Qty 1 IR Receiver (Everlight IRM-8420) (other source:Link)

Step 4: Connecting the Components

Carefully follow the schematic and place the circuit in a bread-board. 

Note that while the voltage regulator is not shown in the prototype it is needed to drive the IR receiver. During this prototype I used a 5V source to measure the correct distance where I wanted the sensor to work.

Step 5: Testing the Circuit

Here is the video of the final outcome. At the end of the day the circuit will need to be moved to the garage and adjusted at the distance that you will have your car at. 

The main draw back of this circuit is that it is always on. For our next instructable I will add a photoresistor to latch power on when lights hit the sensor, with the assumption that the garage will be dark most of the day (no windows in mine)

Until the next time

Are there any backup safeguards for the person who becomes dependent on the sensor, but does not realize its battery is dead? Might such a person drive into the wall because his or her attention was focused on an LED that is not going to light because of the dead battery? Also, the bodies on cars have irregular curved surfaces that will encounter the IR beam differently each time the car enters the garage unless the car is in exactly the same position each time it is driven into the garage. That could mean the detector is no longer able to receive the signal. <br> <br>I like what you have done. I am not sure it has adequate provisions against contingencies that could render it ineffective. <br> <br>I have often thought a good system would involve a light beam of some kind that would be broken when a car pulled into the garage.
Like this. https://www.instructables.com/id/Automatic-garage-parking-aid/
Thank you for this link. We use a foam ball from the ceiling. It contacts the windshield when the rear bumper is far enough inside the garage for the door to clear it well. I like the idea of a mechanism to raise the ball out of the way, although there are times in the colder months when I move cars out of the garage and close the door so I can have more workshop space inside.
We use a couple of 4x4's on the floor where the rear tire needs to stop. <br>
This is an interesting way of doing it, but it is not a lot cheaper than if one used a Attiny85 microcontroller and either the IR route you chose or an ultrasonic sensor (which can be bought for $1 on ebay). The main concern I have is the stability of your oscillator frequency using a simple RC timing. I bet it will vary with age and with temperature (inside of garages get really hot in the summer, cold in the winter). A 10% change in frequency may cause the IR receiver not to demodulate the signal. Lastly: if you used 3AA batteries, instead of the 9V battery you could have saved the voltage regulator (and the circuit would run a lot longer too).
You will get a longer run time if you replace it with a 7555 timer which uses only 60 uA instead of 6 mA.

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