9. Input Devices

Goals

group assignment:

  • [x] probe an input device’s analog levels and digital signals

individual assignment:

  • [x] measure something: add a sensor to a microcontroller board that you have designed and read it

Tools Used

TLDR; Nice images

Group Project

I probed by photo sensor using a multimeter and an oscilloscope. I found the small oscilloscope in our lab hard to use but one of the other team members had a desktop one that was much easier to use.

The most interesting results were using a torch to illuminate the sensor while it was connected to the oscilloscope. The sensor was able to detect the light and the oscilloscope showed a clear signal.

Summary

The step by step can be found on the group site.

Individual Project

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1. Visible Light Phototransistor

I have been struggling with the electronic portion of the assignments so I have decided to focus on simple boards that have already been designed so that I can focus on learning the details of making the board.

To this end I am one again using the work of Adrián and I made his photo sensor module.

A phototransistor is a special type of transistor that reacts to light instead of electrical signals. When light hits it, it allows more current to flow, making it useful for detecting light levels.

1.0 (re)Design

I downloaded the relevant files from Adrian’s Fab Xiao Page This included Eagle files and PNG’s

I wanted to use KiCAD a bit this week so I opened the Eagle files using File->Import Non-KiCad Project

The schematic is relatively simple but it was useful for determining the value of the resistor required and the orientation of the photodiode.

Once I understood the schematic, I wanted to add my personal touch to the PNG’s so I added my company logo into the PNG in GIMP

1.1 CAM

For the CAM, as described last week we were short of 0.4mm endmills so I made use of my strategy using the 60deg V-Bit.

  • 0.05mm depth of cut
  • 20% stepover
  • 7no offsets
  • 240mm/min feedrate

I think the low stepover combined with the high number of offcuts makes sure that the copper is isolated from the rest of the board, even with a low depth of cut.

1.2 Making

After cutting my board I retreved my components from the workbench.

used a small vice while soldering. I feel like my technique is improving here. they key steps I am following

  • 420deg on the iron
  • place the component nearby on the board, within poking distance of the pad.
  • Hold the tip to the pad
  • Count to 5 in my head
  • Add solder to the pad (not the tip as I was prone to do before)
  • Poke the component into the pad
  • Position the component so that it lines up with any other pads it needs to connect to
  • Hold component in place using tweezers and remove iron.
  • Say a little prayer
  • Then repeat the first few steps on the other pads, making sure to let the pad heat up first.

Continue soldering components until all pads are connected.

I was unsure of the orientation of the phototransistor so I checked the data sheet and the green marks on the ‘collector’ side of the sensor point towards the pin where the other side points to ground.

Completed board with much improved soldering.

1.3 Testing

I used the multimeter to check the continuity of the circuit and all was good.

I wanted to test out the code that Adrián used to read values from the sensor but he was written in Arduino C and I am trying to work in Micro Python as that is what ill be using for my final project.

So with some help from ChatGPT, I was able to convert the code to Micro Python.

I then modified the code to output the values to the prompt every 2 seconds as that was easier to test with covering the sensor with my hand for photographs

And thats the completed board with the sensor running.

In Summary

This week was a big improvement for me. Soldering is starting to become slightly more natural and I am starting to understand the logic behind the code better.

The cutting of the board was also much easier than last time. I think for my next board that I am designing I will be studying exactly how Adrians board was set up so I can replicate it.

Things I would do differently next time

The last two weeks I have leaned pretty heavily on pre designed boards so for next week I need to get outside my comfort zone and try to design my own board.

See below link to to files created this week:

Week 9 Files

End

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