A warning about pushbutton encoders

[Braeden108]

So I recently had an issue with a push button encoder, and I figured out the issue. I'm just passing this information along to everyone so they can avoid this issue if they should come across it.

 

So a push button encoder has 5 pins. 2 for the push button 3 for the encoder. You would think they don't need each other to function.

 

This isn't true. One of the pins on the push button side is the common for the whole encoder. The middle pin of the encoder side is just a duplicate of signal pin. Of course this may not be the case for your encoder, so check your datasheets.

 

But be warned that is a thing.

 

Anyone else have any advice about weird parts? Could be cool to make an advice thread.

Edited April 14, 2017 by Braeden108

[FSFIan]

Anyone else have any advice about weird parts? Could be cool to make an advice thread.

 

The LED backlights of small character LCDs come in different variants.

 

1) Some displays might have two pins that expect a certain voltage to turn on the backlight (i.e. the board includes some form of current limiting, either a resistor or a constant current source).

 

2) These units have two pins labelled "LED" that can be connected with a jumper to turn on the backlight (one is VCC, the other goes through a built-in current limiting resistor to the backlight). If you want an adjustable backlight, you can connect a potentiometer to the pins instead.

 

3) Some displays just have the LED pins exposed directly and you are responsible for limiting the current.

 

Confusing one variant for another can lead to short circuits or fried components.

 

Even if the backlight works, check the current with a multimeter. I connected 5V directly to a variant 3) once, so I was powering the LEDs without current limiting. After a few hours of experimenting, the wall wart I was using to power the whole setup broke. I switched over to my lab power supply. A few minutes later the fan of my power supply turned on -- I was startled because I didn't even know it had one. That finally made me check the current going through the backlight. It was close to 1 amp. I facepalmed and added a resistor to get it down to 20 mA. The lifetime of that poor LED is probably significantly reduced now :D

[Braeden108]

Hall effect sensors aren't wired Ground-Analog Voltage(output)-Voltage like a potentiometer. They're wired Ground-Voltage-Analog voltage(output)

 

I thought they were set up like a pot, and I fried my shiny new hall effect sensors.

[zaelu]

I have for several years 3 encoders connected to a bodnar board and they work without any issues, especially the bush buttons. The rotaries are a bit twitchy and I had to tweak them with a small software for them downloaded from Leo Bodnar site.

 

However, I would like to mod my G940 with hall sensors but I'm afraid I don't kow how to wire them :).

[JG14_Smil]

I usually use these:

 

http://www.allelectronics.com/item/re-30/30-detent-rotary-encoder-with-switch/1.html

 

I think they are Alps. I forget which type I defined them as but they work pretty well. There are some QC clunkers, so I buy a couple extra.

 

Oh! Never trust a power supply polarity. I bought one that was labeled backwards. Use that meter. :)

Edited April 14, 2017 by JG14_Smil

[Sokol1_br]

Opera resume: always check component datasheet. :)

[Krinje]

Mechanical Keyboard Switches (cherry mx) make poor switches for Nav/INU panels (like a PVI-800), far too much travel and not enough click, they may be good for a number pad on a keyboard, not so much on a panel (IMO).

 

Lessons learned right?

[Braeden108]

Yeah, you all are right. I got a little screwed with my encoder. The common ground between the switch and encoder is a right pain in the ass. (I get this one time to use colorful language based on how much of a headache its giving me.)