Cool Components VI: Non-Moving Metal Buttons
While looking into ESD-safe buttons, I discovered quite a few metal buttons with no moving parts.Â These buttons do have some potential advantages including:
- Easier to use in ESD-safe applications (since there is only one part to ground, and many models are made of conductive metal).
- Great durability, up to 50 million cycles or more, since there is no mechanical wear.
- Better washdown and cleaning for medical and similar applications, because they have fewer cracks to hide nasty stuff.
- Better resistance against vandals (since the exposed part is made from one piece of metal).
Potential disadvantages include:
- No tactile feedback; great feedback is one of the best features of a good pushbutton.
- Very limited current switching ability; many mechanical switches can easily handle 10A currents.
- Potential problems with gloved fingers not actuating the button, or with water or nearby objects actuating the button.Â I suspect in most cases you won’t have these problems, but you should verify first, starting with the datasheet.
- 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.Â 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.Â 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.Â Cases are made of plastic, anodized aluminum, or stainless steel.Â Illumination options are none, spot (1 LED), and ring.Â 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.Â 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.Â 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.Â Illumination options are none, point, and ring.Â 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 use a sensing technique similar to capacitive touchscreens.Â They can have problems with gloved fingers; however, Atmel claims that many gloves (including typical household, medical, and clean room types) should work fine.Â 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.Â The CSE 16 models were round metal switches, while the uG models were designed to be used under glass.Â 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.Â The CP line will be available in 16 mm, 19 mm, and 22 mm sizes with anodized aluminum cases.
- Texzec‘s ActiveMetal buttons use ultrasonic energy trapped in resonant cavities. Â Available materials are stainless steel, aluminum, plastic, and zinc alloy.Â Sizes include 19mm, 22mm, and 30mm.Â 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).
I haven’t seen any metal ones, but there are some plastic models, such as theseÂ from Banner Engineering.