This week’s EYE ON NPI (video) is gonna spin you right round, baby, right round like a record player – it’s C&K’s ENC Series Optical Rotary Encoder Switches – a high-reliability encoder with strong detents, that’s great for medical and industrial equipment, automotive, and more, where longevity and reliability is important.
Rotary encoders are a popular user interface element that engineers use to add a tactile increment/decrement control. We find they’re much more intuitive to use than touch screens, especially when you want to increase or decrease a value precisely: its a lot easier to twist the knob by one detent than it is to press a touch screen once. Rotary encoders can also be used hands-free or when observing some output because the tactile feedback is strong.
The most common rotary encoders used for user input are mechanical style, usually with detents. They can be ring-style like the famous iPod Clickwheel or knob style. These are two mechanical rotary encoders in that there is a little leaf spring connected to the knob and the “common” pin, and the body has a metal-cutout piece, that when rotated connects and disconnects the two side pins from the common. The two pins pulse high and low to indicate motion and direction. Usually two interrupt pins are connected to the rotary encoder to catch the pulses and track the counter increment or decrement.
Super fun and easy right? Except….that little leaf spring contact ends up rubbing against the gray code wheel and even good quality springs have a contact life of maybe 500,000 contacts. that’s only 10,000 full turns – each turn is 2 x 24 contacts. if you’re turning the knob 10 times a day the encoder will fail after 1000 days, about three years. And rotary encoders do fail, a lot! Heck, even our favorite scope we got right out of school has a broken encoder on the channel 1 zoom select (not surprising, since channel one is the most used and its turned constantly to zoom into the signal). A bad encoder may not be user-serviceable at all, and requires some care to desolder and replace – unless it’s on a detachable cable or module, it can be a very serious repair. Flaky encoders are also a little dangerous – they can increment instead of decrement, which can be confusing and cause incorrect settings.
If you’re designing a medical device or a car where there’s a knob that will be used daily, having it fail after 3 to 5 years is not going to be an option – especially since the failure can happen instantly. Not a good look when a $2000 product is taken down by a $2 encoder failure. Enter the optical encoder! Optical encoders solve the contact rating issue by replacing the leaf spring with two LEDs and an optical sensor. Instead of mechanically contacting the two grey code bits, the optical sensor provides the pulses without the risk of wear and tear. These cost a few dollars more than your everyday mechanical encoder but give you rock solid reliability.
These C&K ENC optical encoders look and feel just like mechanical encoders. With 24 detents, they’re a drop-in replacement. You can panel mount them and there’s even a quick-replace connector with JST SH 6-pin socket, for easy replacement in the field.
The C&K ENC Series Optical Rotary Encoder Switches are in stock right now for immediate shipment from Digi-Key! Order today and you’ll be reliably twistin’ and turnin’ by tomorrow afternoon – don’t forget to pick up some JST SH cables as well!
