Hall Effect Pushbuttons

Hall effect pushbuttons are cool because they have a stroke, like a mechanical pushbutton, but can last for millions of cycles.

• ITW Switches has a wide variety of hall effect pushbuttons, including metal and illuminated large panel mount switches, such as the Series 48SS, the 48M-SS, 57M-SS, and 58M-SS.  However, availability is poor; for example at Mouser I only found a few 48SS models (but they were all less than $20).
• C&K has the HP series.
• APEM has the IH Hall Effect Switches.  The IHS models are panel mount switches start at ~$40.  The IHL models are unique: they have a linear 0.5->4.5V analog output over the switch’s 4mm travel, and cost ~$60.  However, I think a T-Bar or one axis joystick would be a lot easier to use, although they would typically be larger and more expensive.

Finally, I have to mention Schurter’s MSM CS series: they are mechanical vandal-resistant switches with a ceramic actuator.  The ceramic material makes for a very cool looking button; see the PDF datasheet for pictures.  Prices start ~$25.

1. Easier to use in ESD-safe applications (since there is only one part to ground, and many models are made of conductive metal).
2. Great durability, up to 50 million cycles or more, since there is no mechanical wear.
3. Better washdown and cleaning for medical and similar applications, because they have fewer cracks to hide nasty stuff.
4. Better resistance against vandals (since the exposed part is made from one piece of metal).

Potential disadvantages include:

1. No tactile feedback; great feedback is one of the best features of a good pushbutton.
2. Very limited current switching ability; many mechanical switches can easily handle 10A currents.
3. Potential problems with gloved fingers not actuating the button, or with water or nearby objects actuating the button.  I suspect in most cases you won’t have these problems, but you should verify first, starting with the datasheet.
4. High prices, typically $20-$100 (although a comparably sized mechanical button is typically $15-$30).

I found buttons from Schurter (Switzerland), APEM (France), Grayhill (USA), Texzec (USA), C&K (USA), EAO (Germany) and Barantec (Israel); there may be others, too.  I think it’s interesting that almost all of these companies are either European or American.

There appears to be a limited market for this switch type; several companies have dropped lines soon after introducing them, and ITW Switches sold its ActiveMetal line to Texzec.  I’ll mention some of the “missing in action” lines below.

So here are some of the more interesting switches I found, sorted by sensing type:

Piezo Electric Buttons

• Schurter has the PSE line of piezo switches, available in 16 mm, 19 mm, 22 mm, 24 mm, 27 mm and 30 mm sizes.  Cases are made of plastic, anodized aluminum, or stainless steel.  Illumination options are none, spot (1 LED), and ring.  Prices range from ~$20 (CSE 16 plastic), ~$25 (CSE 16 aluminum), ~$45 (CSE 16 stainless) and up.
• Grayhill has the 37F series of piezo buttons.  Cases are aluminum, and prices start ~$20.
• APEM has the PBA series, available in 16mm, 19mm, and 22mm bushing sizes, with and without illumination, and with anodized aluminum or stainless steel cases.  Pricing starts >$30.
• Barantec has a wide range of piezo buttons in 16 mm, 18 mm, 19 mm, 22 mm, and 27 mm sizes encased in aluminum or stainless steel.  Illumination options are none, point, and ring.  Barantec only sells direct in the US.
• C&K had the KP series of piezo buttons back when they were part of ITT Canon, but they are no longer available.

Capacitive Buttons

• Capacitive buttons use a sensing technique similar to capacitive touchscreens.  They can have problems with gloved fingers; however, Atmel claims that many gloves (including typical household, medical, and clean room types) should work fine.  The buttons can often work through a thin non-conductive layer such as glass.
• Schurter had several lines of capacitive switches, including the CSE16, CSE 15 uG and CSE 25 uG.  The CSE 16 models were round metal switches, while the uG models were designed to be used under glass.  Mouser still has a few CSE16 switches left at >$90.
• EAO had the Series 75 capacitive touch buttons, but they are no longer available.
• APEM has just introduced the CP line of capacitive buttons; as far as I can tell, they are not yet available.  The CP line will be available in 16 mm, 19 mm, and 22 mm sizes with anodized aluminum cases.

Ultrasonic Buttons

• Texzec‘s ActiveMetal buttons use ultrasonic energy trapped in resonant cavities.   Available materials are stainless steel, aluminum, plastic, and zinc alloy.  Sizes include 19mm, 22mm, and 30mm.  As far as I can tell, Texzec has no distributors; however, Newark is selling the last of the ITW ActiveMetal buttons for ~$35 (22mm, zinc alloy).

Optical Buttons

I haven’t seen any metal ones, but there are some plastic models, such as these  from Banner Engineering.

I first researched metal buttons because I needed an ESD-safe button, and I couldn’t find one.  Plenty of buttons have specs for ESD immunity, but I needed one that wouldn’t cause ESD (Electro-Static Discharge).

ESD can create a high voltage spark which can kill nearby sensitive electronic circuits.  Everything close to the ESD-sensitive part needs to be either conductive and grounded or dissipative (material with resistance of 10^6 to 10^9 ohms/square so current will flow, but not too rapidly) and grounded.

Normal plastic is especially bad, because it is an insulator, and can be tribocharged: friction caused by rubbing the plastic part can create a large static charge.  You can get dissipative plastics, but I don’t know of any buttons that use them.

Anodized aluminum is also an insulator; for an ESD-safe aluminum part you have to use electroless nickel plated aluminum.  For example, Banner’s ESD safety light curtains use electroless nickel plated aluminum for the bodies and static dissipative plastic for the optical covers (BTW, as far as I know, they are the only readily available ESD-safe light curtains).

You can’t reliably ground through a moving part.  So if a button has a moving button, then the moving part has to be grounded with a ground wire as well as the stationery part.

While there aren’t any buttons that are advertised as ESD safe, there are some that might work.  What characteristics would help?

1. Be able to ground the both the body and the actuator.  A single piece, non-moving body is ideal if it can be grounded and is conductive or dissipative.
2. Everything that an operator could touch must be made of conductive or dissipative materials such as stainless steel.  If the button is illuminated, the plastic lens would have to be made of dissipative material.

So what are some possible solutions?

1. One piece conductive metal buttons, such as a Schurter 1241.2611 PSE16 16-mm stainless steel piezoelectric button (~$45) or a Texzec T01-012203 22-mm stainless steel ActiveMetal ultrasonic button.
2. Two piece conductive metal buttons such as a stainless steel vandal-resistant pushbutton (available from Schurter, ITW, and many others).  As noted above, you’d have to figure out how to ground both pieces.
3. Use an ESD-safe cover: cover a regular pushbutton with a fixed body that captures a moving part (to depress the button’s actuator); the cover parts have to be conductive or dissipative.  One advantage: if you use a clear, dissipative plastic for the moving part, you can use an illuminated pushbutton underneath.  This ESD-safe cover will probably cost substantially more than the pushbutton.
4. Spray on anti-static spray.  Although anti-static spray should help short term, I’m skeptical that it will continue to work well for a substantial period of time.

All of these possible solutions would have to be verified: you will need to verify that all external parts of the button are grounded and that the button will conduct or dissipate any static charges.

LCD Switches from NKK, ScreenKeys, and E3

These pushbuttons aren’t well suited for the typical system integrator.  They’re all designed to mount on a PCB, use a SPI interface (readily available on microcontrollers, but not on PCs or PLCs), and require complex programming.

Most models use a monochrome LCD with a backlights of varying complexity.  Here’s some product highlights from the three companies I know about:

NKK SmartSwitches

NKK has the best distribution by far; their distributors include Mouser and Digikey.  NKK has the widest product range, with prices ranging from about $45 to $80.  NKK also the most support; for example, I’ve seen SmartSwitch articles in Circuit Cellar Ink.

• Basic buttons include 36×24 and 64×32 monochrome LCDs with single, bicolor, and RGB backlights.
• The OLED models provide 65536 colors with a 64×48 pixel resolution, with prices around $80.
• The OLED rocker switch is unique; it includes a white monochrome 96×64 pixel OLED display, and is also around $80.

ScreenKeys

ScreenKeys is an Irish company with some normal and one unique product.

• Basic buttons include 32×16 and 36×24 monochrome LCDs with bicolor or RGB backlighting.
• The unique product is the TFT128 button, which has a 128×128 pixel, 65536 color TFT LCD display.  One minus is that the TFT128 uses a flat, LCD-style cable for communications.  SparkFun used to carry it at a reasonable price (~$50 IIRC), but does not anymore.

[E³] Engstler Elektronik Entwicklung GmbH

[E3] is a German company that makes pushbuttons with 32×16, 36×24, and 64×32 pixel monochrome LCDs with RGB backlights.  The RGB backlights provide either 64 or >10,000 calibrated colors.

The SB6432 is available on-line from FunGizmos for $36.

Summary

I’d still like to have an excuse to use one of these buttons in a project; maybe someday…

A typical switch mode power supply, however, is designed for tight voltage regulation, does not have a shunt and handles over current by limiting current to its maximum rating.

Some switching power supplies are better because they have 20% to 50% peak capacity for a brief time.  I’ve seen this capability in models from Cabur (sold by ASI in the US), Puls, and Delta; I’m sure there are other examples.

I’ve used the Delta CliQ series for servo motor power, and so far they’ve worked well.  The CliQ can handle 50% over current for 3 seconds, the pricing is quite good (under $150 for 24V at 10A), but they’re only available for 12V and 24V.

The first designed for motors SMPS I discovered was the IMS ISP200/300 series, which are unregulated switching supplies specifically designed for handling the rapidly changing, inductive loads typical of stepper motors or DC motors.  IMS is now Schneider Electric, and they have discontinued the ISP series.

I don’t really consider the Galil PSR series a SMPS for motors; it looks like an ordinary enclosed switcher with an added shunt resistor.  The PSR costs $250, and is available in 24V at 12A or 48V at 6A.

I recently discovered a second SMPS for motors, the Cabur XC series (sold in the US by ASI).  They have a 72-85V output at 3.1A, 6.6A, or 13.3A, have a 20% reserve capacity when <45C, can handle 50% over current for 5 seconds, and have output over-voltage protection (equivalent to a shunt).

It’s interesting to compare the XCSF500G (72V at 6.6A) to the Logosol LS-872.  Logosol makes my favorite linear power supplies (I own a LS-1148 and use it extensively); they are relatively compact, are switch selectable between 115V and 230V input, have ESTOP inputs, front panel mount fuses, and are available in a variety of output voltages.  (The only other 120V/240V switch selectable linear motor power supply I’ve been able to find is Copley’s  DP models in their PST series, but they cost much more).

My favorite  brand  is Microscan; I’ve also used other brands with good results.  The Microscan QX-870 is a typical  barcode scanner: it has 10 scan lines, can do 300 to 1400 scan/sec, has  a read range of 1″ to 30″, can read all the normal 1D barcodes (UPC, Codabar, Code 39, Code 128, etc)  as well as the PDF417 and Micro PDF417 2D barcodes.

However, most 2D barcodes (such as the popular Datamatrix) need an area sensor.  In other words, you can’t use a laser scanner, you have to use a camera.  Now finding a lens that has a 29″ depth of field (from 1″ to 30″) is challenging.  Of course, the barcode reader could use autofocus, but with a normal lens, that adds a lot of complexity, cost, and still isn’t perfect.  One Microscan 2D barcode reader had a halfway solution: the reader could cycle through a preset set of focus positions until it found a good read.  I wasn’t impressed (although to be fair, I never tried that model).

To make matters worse, Datamatrix codes are often used in direct marked applications; for example, using a laser or ball-peen to create a barcode directly on a metal aircraft part.  Creating lighting that is affordable, compact, and can work on anything from a shipping box to a reflective metal part is hard.

I’ve thought for a long time that liquid lenses (now available from optical suppliers such as Linos) could solve the depth of field problem by allowing affordable and rapid autofocus.  Well, they’re here (and both claim to be “the first”): Cognex has the Dataman 200 series, and Microscan has the QX Hawk with liquid lens and modular zoom.

I think this is a big deal; for example, the QX Hawk claims a read range of 1″ to infinity.  Unfortunately I don’t have any personal experience with either reader, but if I need to read 2D barcodes in the future, I will definitely check both out.

IDEC LW7L Push Buttons

Industrial style does matter.   That’s one reason I like IDEC’s LW7L flush mount pushbuttons.  Recently I was looking at some of our old equipment with Telemecanique pushbuttons that stick out over 5/8″ — those buttons are functional, but look dated.

The LW family of buttons is extensive (well over 10,000 combinations are available), but the models I like are the  LW7L-M1C64MG and similar.  What is good about them?

• They only need a light touch to operate (lighter than some other IDEC push buttons such as the HW2L series)
• High quality
• Long life LED lights available in amber, green, red, blue, white, and yellow.
• Powered directly by 24V (no resistors to worry about — I’ve destroyed LED lights from other companies).  6V, 12V, 120V, and 240V models are available, but I always use 24VDC.
• They are easy to install.
• The price is reasonable (around $30).  The Telemecanique buttons were much more expensive.   They aren’t the cheapest (e.g. the HW2L buttons are about $20), but I think the difference is well worth it because of the next point.
• They look great, with the square shape and flush mounting.  The traditional round, stick out 22mm push button makes equipment look like a retro-encabulator from the 1950′s.  I consider the extra cost over the HW2L buttons a marketing expense.

I also really like IDEC’s XW series of E-STOP switches — especially the models with a LED light.

Today’s focus is piezoelectric motors.

A piezoelectric material generates an electrical potential when stress is applied.  The reverse piezoelectric effect is when applying an electrical potential creates a stress in the material, changing its size slightly (typically by 0.1% or less).  This change in shape can be used in several different ways to create motion.

I first heard about piezoelectric motors back in the 1980′s when Canon introduced the traveling wave ultrasonic motors with their EOS autofocus camera system.

The first industrial piezo motors I heard about where piezo actuators, which just use the change of size in the piezo material to create movement.  This motor type is highly accurate (<1.0 nm), but the maximum move size is very small (typically <100 micron, although I’ve seen up to 500 microns).   For longer moves, you have to combine a traditional stage with the piezo actuator.  A variety of companies make this motor type; the ones I think of first are PI (Karlsruhe, Germany) and Mad City Labs (Madison, WI, USA).

Then I heard about the Nanomotion (Yokneam, Israel).  Nanomotion motors work by driving a piezo leg against a ceramic plate in an ellipse at high frequency.  Their industrial motor capabilities include:

• The same motor can be used for linear or rotary motion (with circular drive strip).
• When power is off, the motor holds the current position.
• Travel up to 2000 mm, speeds of over 200mm/sec
• Force up to 3.2 kg-f
• Motor can be operated in DC (actuator) mode to provide nanometer level precision.
• Good for some specialized applications, since the motors are non-magnetic, and vacuum-compatible versions are available.

You must use a Nanomotion amplifier; analog input is standard,  but  a CANOpen interface is available (it’s more expensive, since it uses the same analog amplifiers internally).  The amplifiers generate the high voltages (around 300V IIRC) required to drive the motors.

Nanomotion also sells high precision linear and rotary stages.  The rotary stages start around US$5000; just a motor and drive combo is around $1000 (but as always, check with Nanomotion for exact pricing).  Allmotion is now selling drives (controller and amp) for the Nanomotion HR series; pricing starts at $395.

A few years ago Nanomotion was acquired by Johnson Electric, a large Hong Kong-based manufacturer of motors and such, since Johnson Electric wanted to use their technology for cell phone camera modules.  Now Nanomotion produces small motors, zoom lenses modules, zoom camera modules, and custom driver ASICs, although you might need to be a high volume OEM to buy some of those products.

Next I heard about Piezo Motor AB (Uppsala, Sweden) which makes the Piezo LEGS and PiezoWave motors, which are also sold by Faulhaber (MicroMo in the US).  This Faulhaber link gives a nice summary of the standard PiezoWave linear motor and Piezo Legs linear and rotary motors.

At Photonics West a few years ago, I discovered DTI Piezotech (Sarasota, FL, USA) and New Scale Technology’s (Victor, NY, USA) Squiggle motor.

The Squiggle motor works by creating ultrasonic vibrations that cause a nut to travel in or out.  They are oriented towards small, large volume applications.  New Scale’s standard motors range from 6mm travel and 0.3N force to 50mm travel and 5N force.

New Scale has an extensive product line, including standard motors, custom motors, driver ASICs, driver boards, development kits, USB control and driver,  standard stages, and magnetic position sensors.

New Scale has a web store that sells a variety of their products — I like it!

DTI Piezotech is part of Discovery Technology International which makes bioinstrumentation.  Their initial product was a rotary motor (the first I heard about); IIRC, initially they only sold the motor as part of a complete, high precision stage.  Now they have really broadened their product line, with a variety of sizes  of both linear and rotary motors.

Standard rotary motors range from 2 mM-m to 6 N-m force; linear motors go up to 50N-m and 1,000 mm/sec.  Like Nanomotion, DTI linear motors can also operate in actuator mode for ultra precise positioning.   I couldn’t find much information on their drivers, but they do have development kits, with controller boards, available.

One of my readers (thanks, Bob!) mentions yet another company, Elliptec (Dortmund, Germany), with yet another approach (piezo controlled lever moving a gear seems like a decent description).

I took a quick look at PI’s web site; they now sell a broad range of piezo motors, including actuators, rotary motors, and linear motors.

Finally, while doing research for this post, I came across PCB Motor (Hillerod, Denmark) which makes parts that can assembled on PCBs to create motors on printed circuit board.  They have on-line ordering of their development kits.

BTW, the wikipedia piezoelectric motor page is pretty weak – it doesn’t cover most of the companies or approaches I cover.

I learned a lot writing this blog post – I hope you enjoy it!

Update Feb 2011: Another company making piezo motors is CEDRAT of France.  They make short range piezo actuators with their own technology, such as the APA (amplified piezo actuators).

PI’s products are definitely not inexpensive, typically at least several thousand dollars for motor and controller (that’s not to say they aren’t worth it, but I like to have an idea of costs).