10 July 2021

PROJECT: Half-Life 2 AR2, Update #11 - Receiver Sensor PCBA's

"Quick" update, I have just finished designing the left & right reciever sensor PCBA's (the ones that figure out position of solenoid plunger/firing pin). Next step was to place them into the AR2 assembly to check for possible collisions (see first section), and to see how well the IR LED & IR sensor pair are expected to function (see second section)

PCBA & Solenoid Plunger Collision

From my AR2 prototype I noticed that the solenoid plunger (pink thing below) has quite a bit of slop, and at the extreme case can move around by ~1mm

The components that are of most concern are the electrolytic capacitors (Nichicon UCQ1E100MCL1GB), as these are the highest items on the PCBA (coming in at a whooping 4.6mm). Below I found that on the IR sensor PCBA was heading for a collision, so I had to move the electrolytic capacitor (on both PCBA and AR2 assembly) as far down as I possibly could

IR LED & IR Sensor Viewing Angle

As mentioned in a previous post, I am using two IR LED & IR sensor pairs (in a line of sight arrangement) to figure out the location of the solenoid plunger

Doing a quick test with my selected LED (Stanley Electric VTAN1116P-TR) I saw that the 40° viewing angle should not be an issue, as at no point can a single IR sensor see light from both IR LEDs (think viewing angle cones having too much overlap)

However if you increase the IR LED viewing angle to 60° (SunLED XZTNI53W-8) you will have issues with loading configuration D and possibly E, as here the viewing angle cones overlap too much and so can confuse the IR sensors

But wait there is more! If you have a closer look at the datasheet for 40° viewing angle IR LED (Stanley Electric VTAN1116P-TR), you will see that: 

  • At 40° the LED has a 50% relative intensity
  • At 140° the LED has a 20% relative intensity

Meaning I am likely to run into the overlap issue with configuration D, as the IR sensor will probably pickup the stray IR light. I won't know if this is a problem till I build the reciever assembly, but if it is then I could either:
  1. Narrow the viewing angle of IR LED by making a cylindrical cover
  2. Read the analog voltage of the IR sensor (via ADC or comparator) and then trigger on a set threshold

To finish off... Believe it or not but the IR sensor (WE 1540601NEA200) also has a viewing angle, which is 120°. Luckily with the IR LED & IR sensor PCBA configuration (not angle between the two boards) should not have any issues