How to shield a live wire at 240V ?

[marconi]

q12x Good afternoon. I spent a couple of hours on my version 3, the one which uses pulsed ir light rather than continuous illumination in versions 1 and 2. The pulsing is about 100kHz. The received waveform produced by the ir sensor array is displayed in yellow in the video clip below. The amplitude of the received waveform, which is the combined output of the four photodiodes, varies with the proximity of the hand. I cannot remember if I showed you this variation before. What I did this afternoon is construct a peak detection circuit the output of which is displayed as the blue horizontal line on my scope sitting on top of the peak amplitude of the yellow waveform. Unless my finders are in front of the array it is detecting the side of my scope. You can see the voltage output by the peak detector in Blue following the amplitude of the received Yellow waveform. It is this Blue signal which I will input to my 8 comparators. I will look at the output of the comparators only when the ir illuminators send a pulse of light in order to distinguish between this illumination and background illumination.

How are you getting on? Regards

marconi

 

[marconi]

q12x. Good afternoon Sir.

I thought you might like to see a little more progress albeit at a snail’s pace. You know in Version 3 I pulse the ir illuminators on and off and its is this reflected flashing light which the photodiodes receive as well as any background ir light. The photo current of these photodiodes is converted to a voltage which is passed to a peak voltage detector. I thought I would plot the peak voltage at the output of the detector against distance for ir illuminations on and off. The simple test rig is in the first image and the plot in the second. The white piece of paper in the blue clamp is my test ‘hand’ moved along the 15 inch rule towards the sensor array. The steady voltage in red for ir illuminators off is about 60mV and shows the background ir is making no difference to the peak voltage detector output as the hand is moved. You can see the On peak voltage signal is clearly separated from the ambient only off signal. With further signal processing l hope to make Version 3 tolerant to background ir illumination.

 

[marconi]

-q12x- I have attached a picture of my V3 comparator board to demonstrate to you I am making progress. It uses this comparator which interestingly can operate from both dual tailed supplies and single tailed 0-5V ones.

https://www.ti.com/lit/ds/symlink/lm311.pdf?ts=1620973425640&ref_url=https%3A%2F%2Fwww.google.com%2F

 

[marconi]

q12 A little more progress. The second attachment is a view of the breadboard for Version 3 with circuitry to produced pulsed ir illumination, reception of ir pulsed reflections, peak reflected signal detection and a to d conversion to drive the rule of 8 LEDs. You can see in the first attachment the rule of 8 LEDs lighting up as the hand is moved closer and further away from the sensor. This set up is showing permanent pulsation of the ir illumination. The next step is to have repeated bursts of ir pulsed light so that in between bursts one can detect just the ambient background ir received by sensor.

 

[marconi]

q12x. Good morning from rainy London.

A little more explanation. Version 3 uses pulsed ir illumination. But of course as well as the pulsed ir being reflected off anything in front of the sensor array producing a received signal component Rp there will also be received a component of reflected ambient ir Ra and direct ambient ir light Da. The total received signal is therefore Tb = Rp + Ra + Da. This is what is detected during the bursts of ir illumination.

Between bursts the illumination is off so what is received is only Ra + Da = T

If then one detects, measures and stores Tb and T, then the difference can be produced Tb - T which is the signal Rp just due to ir illumination reflected off the hand.

The next step then is to measure T.