How to configure an Arduino GPIO as an input

Hi Sean,

I'd do the same as James mentions, heavily reduce the 47k resistor. Also, you could check with your 'scope if you're picking up electrical noise, since it's highly likely with model railroad that you've got mains wiring nearby, on the floor, for example mains cables and power supplies. Twisted pair might not be very effective for electric field based noise, coax would be better.

Also, it doesn't help that the threshold for logic high is quite low, perhaps just a fraction of a volt (with some 3.3V logic families, or a bit higher for 5V). There are more elaborate circuits for inputs, that could involve using a transistor and resistors arranged to switch at a higher threshold (e.g. several volts to be a logic '1'). In other words, behave more like (say) RS232 levels instead of 5V CMOS etc. Also, although technical overkill, the simplest way could just be to use an optocoupler if you just wanted a simple quick-to-build (but more expensive) life.

None of this addresses debouncing, but the methods mentioned by everyone above would work (or just do it in software). There are nice ways to combine hardware and software to have a hybrid approach, but that increases software development time and hardware time. But would be very rugged options. One hybrid approach is to use an I2C I/O expander. They have an interrupt pin. You can trigger on interrupt, and then read the inputs. Apart from the fact that it needs the I2C library, it actually simplifies the software structure since there's no need to do polling.

Hi Sean,

I'd do the same as James mentions, heavily reduce the 47k resistor. Also, you could check with your 'scope if you're picking up electrical noise, since it's highly likely with model railroad that you've got mains wiring nearby, on the floor, for example mains cables and power supplies. Twisted pair might not be very effective for electric field based noise, coax would be better.

Also, it doesn't help that the threshold for logic high is quite low, perhaps just a fraction of a volt (with some 3.3V logic families, or a bit higher for 5V). There are more elaborate circuits for inputs, that could involve using a transistor and resistors arranged to switch at a higher threshold (e.g. several volts to be a logic '1'). In other words, behave more like (say) RS232 levels instead of 5V CMOS etc. Also, although technical overkill, the simplest way could just be to use an optocoupler if you just wanted a simple quick-to-build (but more expensive) life.

None of this addresses debouncing, but the methods mentioned by everyone above would work (or just do it in software). There are nice ways to combine hardware and software to have a hybrid approach, but that increases software development time and hardware time. But would be very rugged options. One hybrid approach is to use an I2C I/O expander. They have an interrupt pin. You can trigger on interrupt, and then read the inputs. Apart from the fact that it needs the I2C library, it actually simplifies the software structure since there's no need to do polling.

Thanks for the commentary. My application of an Arduino's to support animation in model railroading is all about simplicity. I'm currently conducting a workshop with a local model railroad club using video conferencing. The workshop is one workshop session each week for five weeks. The goal is to provide sufficient information for them to determine if microcontrollers are something they want to invest in for their layouts. Most participants are in their 60's with little to no technology type backgrounds.

All those that attend have NO microcontroller experience. The group has managed to gain enough knowledge and comfort to successfully program the blink routine. In the next three weeks they will explore lights, motion (motors) and sound. This involves building the circuits, deploying code and then if it doesn't work determining is the problem in the physical world or the coding world.

The issue with transient triggering causes me concern only because the participants have little experience with electronics and microcontrollers to troubleshoot issues. The circuits they are demo'ing are simple with minimal construction. I have to be cognitive of solutions to the problem so it can help and not hinder my target audience.

Microcontrollers as logical switching devices are new to me. I fostered a career in relays and TTL controllers. I haven't seen the de-bounce issue with Pi projects so it was a surprise to me.

The support has been great. Before I award the atta-boy award (Question Answered) I wanted to give the solutions a try. I like both the code and the resistor. The resistor being the simple solution.

When I was using an RPi last summer, I found that the inputs tended to float.

Making sure that you have the inputs and outputs properly grounded is a must do.

DAB

I have used the internal pull-up with some success.

I now have a buffer interface between the Pi and external connections. Working with groups of people that have little experience with electronics the buffer devices has saved replacing Pi's.