A Very Simple Proximity Detector




Gadget freaks, model railroaders, roboticists or cat-hosts will love the versatility of the Sharp IS471 infrared proximity detector. It is the size of a transistor, operates over the 4-16 volt range, and can detect objects about 4-9 inches away by reflected IR pulses.
The basic implementation requires only the IS471, an IR LED and a 9 volt battery and can be built by most any tinkerer in less than 10 minutes.

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Step 1: Gather the Parts

The parts you'll need are:
1) the Sharp IS471 (available for $2 at: http://www.junun.org/MarkIII/Info.jsp?item=46 or $3 from www.digikey.com, and others)
2) a 940nm IR emitter (such as the Fairchild QED-234, available from www.mouser.com for about 50 cents, and other sources)
3) Something to mount the above two items on. You've got a lot of options here. There are several excellent Instructables on making your own PCBs. If you want to try it out before doing the etching thing you can use a pluggable breadboard (not shown) or go with a small piece of perf-board (pads on .100" centers, shown at bottom left).
4) 9 volt batter and battery clip
5) Soldering iron & solder, diagonal cutters (if not going the breadboard route).

If you'd rather not etch, but still want something snazzy you might drop me a line about the very small custom perf-boards I had made at www.pad2pad.com (shown at bottom right), priced at $2 each for the bare boards, postage included).

Step 2: Putting It Together

Insert the leads of the IS471 into the perfboard close to an edge. The leads will need to be spread out just a bit, since they are spaced more narrowly than the average perfboard holes/pads. Note that the flat side of the IS471 needs to face outward, since this is the side that "sees".

Bend the IR LED to the right as shown below. With the LED positioned as shown the short lead (the cathode) is on top.

Step 3: Mount the IR LED

The LED is best mounted to the bottom of the perfboard as shown below. The board will act as a light barrier, so the IS471 will only see light that is reflected off objects rather than direct illumination from the IR LED, though you may need to add a strip of black tape when assembly is completed to prevent the IR pulses from shining through the holdes in the perfboard.

Position the IR LED so the short lead (cathode) of the IR LED is two holes behind pin 3 of the IS471, and the anode (long leg) of the LED is two holes behind pin 2 of the IS471.


Step 4: Make Some Connections

Time to get the soldering iron hot!
1) Tack down all the pins of the IS471 and the IR LED just to keep them in place.
2) Connect the cathode (short leg) of the IR LED to pin 4 of the IS471 (just bend the leads together then solder to make this connection).
3) Connect the anode (long leg) of the IR LED to pin 1 of the IS471 (just bend the leads together then solder to make this connection).
4) Solder the red wire from the 9volt battery clip to the IS471 pin 1/IR LED anode connection.
5) Solder the black wire from the 9volt battery clip to pin 3 of the IS471.
6) Solder a wire to pin 2 of the IS471. This is the "Low on Detect" signal.

Step 5: Test It!

Now you get to test your new IR proximity detector!

Before snapping on a battery, check your work for solder bridges, there should be no connections other than those given in the previous step.

To test your proximity detector:
1) Connect the battery, then connect the leads from a volt-meter between the black (ground) wire of the battery clip and the "Low on Detect" wire.
2) Point the detector off into empty space and you should see about 8 volts on the meter. (Sometimes just laying it on a tabletop will allow enough reflection to trigger it, so you might have to raise it up just an inch or three).
3) Put your hand about a foot in front of the detector and slowly move it closer while watching the meter. Somewhere in the 4-9 inch range you will see the meter fallto 0 volts. You have been DETECTED!

NOTE: Location and placement is important. Sunshine will "blind" the receiver, greatly decreases detection range. I've found that just a little bit of a sun-shade takes care of this most of the time.

Step 6: Fun Time!

Just making a meter twitch isn't very flashy, especially to your non-geek friends.

How about triggering a Radio Shack 20 Second Record/Play module? This is good for adding sounds to a model train layout, or mysteriously playing the theme from "Twilight Zone" when you wave your hand over it? Or using it to automatically play a startling noise when triggered by your cat jumping onto your work-bench?

Step 7: Mysterious Sounds!

Connect your detector module to the circuit board of the Record/Play module according to the picture below.

Step 8: Controlling a Relay

For larger tasks you might want to use the proximity detector to control a relay.
I've used the circuit below and find it very versatile. You can hang several detectors off it and it will pull the relay if any of them see an object.

Step 9: Whatever You Want It to Do...

The open collector output of the IS471 makes it perfect for so many things it's hard to decide just which way to go.

Robot builders love it for non-contact obstacle detection, pet-owners can use it as a doorbell for their pet doors, model railroaders can trigger sounds or animations without reed-switches or track cuts... heck, I jsut like making things happen with a wave of my hands (just like in the sci-fi movies).

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    126 Discussions


    2 years ago

    OffLogic: First off.....I am - NOT - a "circuit designer"!!! But, I - AM - an "Electronics Builder", in that I am capable of designing various types of mechanical chassis/enclosures/housings - AND - the Printed Circuit Boards which go into my mechanical designs. I thought I would mention that first.

    I am needing a proximity sensor circuit schematic which can be mounted into a 1U rack-mount chassis and be able to detect the opening and closing of a rear rack-door, which would be between 4" to less than 12" away from the sensor. When a technician opens the rack-door, an internal light would turn-on and remain on until the door is closed. Basically, the same thing as a "refrigerator door light".

    I have already designed the rack chassis and have obtained some LED lighting panels as the light source. All I need now is a "hands-free" proximity sensor or a motion detector as the trigger to turn-on this internal rack light. The reason for this "rack-light" is so a technican can work on cables and/or equipment and not have to worry about having a work-light to start with, let alone having to try to hold onto this light or finding a place to clamp it onto. A problem looking for a solution and I've got it. Can you assist me on this here? THANKS!!!

    You can reach me at: arrakis1200@gmail.com




    1 reply

    Reply 2 years ago

    As far as I can understand from what you wrote , you want an internal light controlled by the opening of the door ?

    If you can share an image of the chassis , It would be great .

    Till then , I am pretty sure you can use a Bump switch (240V ) for the light .


    3 years ago

    i need to make a proximity sensor to attach to a toolbox so if someone walks near it will sound an alarm, is there a way of just a single beam with a range of about 2 to 3 feet


    4 years ago on Introduction

    Can I not connect the IR led to the GLout (pin 4)? My understanding of the datasheet is that the sensor only responds to a specific frequency, so the IR led really must be connected to it. I wanted to include an transistor-based amplifier to the IR led so that I can control the range easily by adjusting the gain/current through the IR led.

    Are there other ways to improve the range? What I really want is a proximity detector whose range is easily adjustable (e.g., by use of trimmer resistor).

    1 reply

    Reply 4 years ago on Introduction

    I found IS485/486 to be more appropriate (theoretically) for what I want. Cheaper too.

    Odie Sr.O

    4 years ago on Step 9

    Adding a small piece of shrink tubing to the LED will keep a side view from triggering the sensor.. . . Can be used for directional sensing. . . . I have used this method since I found out that transistors make good light sensors, about 1955. . . Have fun. . .

    Does anyone have a recommendation for a proximity sensor that can detect 1' - 25'? Basically I'd like to make a set of bat-ears for my completely blind grandmother. I'm thinking something that steadily puts out a tone over a 1-ear headphone. Closer things get higher tones, more distant things get lower tones..etc. Any suggestions? I'm a complete noob at this, but I'm smart & learn quickly.

    2 replies

    Reply 11 years ago on Introduction

    I might recommend looking at some of the ultrasonic modules available at www.sparkfun.com or a something IR based on the Vishay TSOP series. Send me an email and we can talk.


    6 years ago on Step 5

    It's possible to add a flip-flop to do this, but the basic circuit alone won't do this.
    The venerable 4013 or a pair of NAND gates can do this nicely.

    1 reply

    Reply 5 years ago on Introduction

    Lemme dig up my notes and codes and schematics for the PIC-based project. It was good to 4 feet or so, I generally was quoting 'one meter' using high output IR-LEDs.
    It was a pretty easy intro to making SMD PCBs then assembling the same the easy way. "I know stuff", as the saying goes.
    Let me get to work on the quick+cheap PIC-based dingus I cooked up using an agile PWM LIDAR (for individuation of competing units)


    5 years ago on Introduction

    Just brouse the Sharp opto-electronics lines on mouser.com or digikey.com you'd be amazed at the sensors out there.


    5 years ago on Introduction

    Laz, nah, it's only rated at 50ma max. Drive a transistor or gang a bunch of 40106 or 4016 to give it a kick easily. Go browse Mouser for driver ICs.


    Reply 6 years ago on Introduction

    I'm not aware of any alternate parts off the top of my head.
    I know they have them in stock here: http://www.junun.org/MarkIII/Info.jsp?item=46.
    You might be able to put something together with a tone-decoder (LM567), led and a phototransistor or something.


    Reply 5 years ago on Introduction

    I was able to make a pretty nifty prox detector that worked at 3-4 feet using a low pin count PIC, IR LED and IR detector. might look at that?