Not Quite Ordinary

When I started writing this review, I didn't even know what category to put this product in.
I'd wanted to try this device for a long time (yes, a button can be a device too), and only got around to it now. That's what I'd like to share with you.
As always, the rest is after the jump.

Unfortunately, I won't be able to use it for now, since it arrived later than planned (not because of slow shipping, but for a few other reasons), and I had to go with a much more expensive solution.

There are various kinds of switches and buttons.
There are the ordinary ones found in every home. You have to press them to turn them on or switch them.
There are touch switches: you don't have to press them, just touch them.
And then there are contactless ones—not in the sense that they have no contacts (though the two aren't mutually exclusive), but because you don't even need to touch the switch; just bring your hand close to it.
That's the last type of device I'll be talking about here.

I'll start, as usual, with a description and photos of what I received, and explain along the way what it is, what it's for, and what similar devices are available.
It arrived in a neat little box. The switch (or, more accurately, push button) was in a clear plastic bag, but I took it out before taking the photos.


Inside the bag were:
The switch itself.
Mounting hardware: two plastic wall plugs and two screws.
Instructions in English, though they're hardly needed for this device: it has no controls to adjust, and the outputs are labeled on the back.
A little piece of paper I couldn't make sense of.


The instructions, in case anyone finds them useful :)


The button itself is very well made. The metal is sturdy, though thin, and looks a lot like stainless steel. The plastic parts fit together well.
It also looks quite nice; the only thing that bothers me is the word Exit. I'll explain why later.


There are 5 wires on the back.
Red and black are positive and negative power, respectively, following the usual color coding (though there are exceptions).
Yellow — relay common
Green — normally open contact
White — normally closed contact.
The wires aren't very long, about 15 cm.


And now we've gradually made our way to the insides.
The device has a double-sided circuit board. The wire functions are also labeled on the back, which is a nice touch: the label stuck to the back could easily come off, get damaged, and so on.
The back cover isn't sealed, but it fits reasonably well. The hole for the wires is oversized, so the protection rating applies only to the front panel.


Logically, the next thing should be a photo of the internals. There will be one, but first, a brief digression.
First, a look at the different types of touchless switches.
1. Capacitive switches require a touch or for your hand to come very close. Probably the simplest and cheapest option. I once did a review featuring one of these sensors.
2. Radio-frequency sensors, which work on the Doppler principle. These are the most expensive sensors.
3. Sensors that detect reflected infrared radiation. A simple, inexpensive, but compromise option.

Now for the pros and cons.
Capacitive sensors are relatively inexpensive, but ideally you need to touch the surface. They may not work correctly in the presence of electromagnetic interference.
Radio-frequency sensors operate at a very high frequency, around 24 GHz. They are complex and therefore expensive, but less susceptible to interference, unaffected by surface contamination, and can work through opaque plastic.
Infrared sensors have a simple design and a range comparable to radio-frequency sensors, but their range may decrease if the surface is heavily soiled, and they don't work through materials that are opaque to infrared.

Now I'll try to explain why I use these switches.
Besides writing reviews and soldering circuit boards, I install automatic sliding doors. These doors don't always come with motion sensors.
And since I install these doors at businesses too, they have to comply with health regulations. These regulations recommend (and sometimes require, for example in operating rooms and restrooms) using touchless door activators. There are even special devices where you have to put your foot in to trigger the switch.

Until recently, I used sensors made by the Belgian company Bea. For example, this one


One of these sensors costs about $130, if I'm not mistaken.
And often you need two sensors for one door.
It's worth noting that these sensors aren't vandal-resistant. The one I'm reviewing is more robust, but it isn't considered vandal-resistant either.

And that brings me to showing you how the IR sensor is built inside.
First, here's the spot where the circuit board goes. You can clearly see the holes for transmitting and receiving IR radiation. They're designed so that the IR receiver only sees reflected radiation.
The circuit board won't work on its own.
By the way, a sealing gasket around the metal perimeter wouldn't go amiss, but the expensive radio-frequency model doesn't have one either.


And now, the device's circuit board.
You can see:
The IR LED.
The IR photoreceiver, the kind commonly used in various remote-controlled electronic devices. Its operating frequency is 38 kHz (measured).
The relay, whose specifications match those given in the manual.
A connector for the wires.
The power input is protected by a resettable fuse and a diode that protects against reverse polarity. Next is a 5 V voltage regulator. There are no electrolytic capacitors, which only improves reliability.
Four two-color LEDs. They glow red in normal operation and blue when triggered.
The control IC is tiny, with 6 pins, in an SOT23 package.


The control IC is marked 02En. I found a description online, but I'm not sure it's the same chip, since the page is in Chinese and looks like some obscure marketplace or forum.
It doesn't just continuously generate pulses to drive the LED; it produces sequences of pulse bursts. The photoreceiver is connected to it, of course.
As a result, it detects obstacles quite reliably. It doesn't respond to an IR remote, or to strong illumination from an incandescent lamp (though that's thanks to the photoreceiver).


Naturally, I measured the current draw in standby and active modes.
In standby, it draws 27 mA at 12 V.


In active mode, it draws a little more—38 mA, since the relay is on.


In standby mode, the backlight is red. It's a little uneven, but perhaps that's intentional.


In active mode, the backlight is blue, but the frosted diffuser keeps it from being too harsh.


The detection range is about 8 cm from a hand and about 15 cm from a sheet of white paper.
It responds very reliably, even to relatively quick hand movements. After triggering, it stays active for about two seconds, then switches to standby.
It doesn't respond to relatively thin objects.


The design is quite slim, with most of it recessed, since it's intended to be mounted flush in a wall or panel.


Just in case, I measured the main dimensions; they might come in handy for someone.


As I mentioned above, the power supply is 12 V, which suggests that the device is intended for use in security systems. The word Exit on it points to the same thing.
Industrial automation systems use a standard 24 V supply and can run on either DC or AC.
I think that with a simple modification, this button could also be used with industrial automation systems.
This button could be very useful in a variety of applications, but the lettering is a drawback. In my opinion, it would be better to offer different lettering options or include stickers with various labels.
Applications —
Access control devices.
Controlling door opening in places where doors need to be opened without touching anything, such as food production facilities, operating rooms, clean rooms, toilets, etc.
Or simply places where this kind of control is convenient, for example, switching on the lights in a kitchen (with suitable cosmetic modifications).

Actually, while writing this review, I had a slight sense of déjà vu. I described similar impressions of a device in my review of the reader. In particular, I really liked the build quality and the fairly well-thought-out, reliable-looking circuitry.

I came across at least two ways to build a similar device yourself online: one using an LM567CN IC, and another using a microcontroller. I built the latter version, and it works well for me. If you're interested, I could review it sometime.

Summary.
Pros.
Price.
Good appearance.
Good build quality and a fairly well-thought-out design.

Cons.
A sealing gasket around the perimeter would be nice.
Since the device can be used for more than just a request-to-exit button, it would be nice to have options for changing the lettering.

My opinion: a perfectly good, simple replacement for RF proximity switches, and it doesn't emit radio-frequency radiation either.

This product was provided free of charge by eachbuyer for review and testing.

I hope this review is useful. I look forward to your questions and comments.
If I forgot to mention anything, let me know and I'll add it.

By adding a dirt-cheap IC (and possibly one resistor and capacitor), you can convert the device to bistable operation: bring your hand near to switch it on, then bring it near again to switch it off. The modification costs about 20 cents; the IC is an HEF4013BP.
As it is, the device works like a momentary button (like the request-to-exit button on an intercom, although this sensor is designed for that kind of use).
I may also review a similar modification later :).