How would you add a hand sensor to this glass?
T Chap
Posts: 4,198
Hello all. I make several custom touch screens out of 1/8" glass that is back painted using a silk screen. There is a PCB on the back that has reverse mounted LED that send light through the graphics( white area). I am re designing the process and getting a UV flatbed printer to print the graphics on the back instead of silkscreen which is such a pain to do for a number of reasons. On the re design I want to add a hand wave sensor that detects a hand within 4-5". I use a Avago(Broadcom APDS-9960 gesture sensor on some LCD type user interfaces and it works great but those methods allow for the sensor to mount in a recesses area in the plastic bezel around the LCD. On the glass, I am trying to avoid having to make a jig on the CNC to create the hole(oval shape) which involves having to cut with water. I've done it a lot but dont want to do that process anymore. The goal is to make a new PCB for that includes the touch sensor copper plane areas, but include some method of hand sensor on the board or attachable to the board. The APDS-9960 specifies max glass thickness of 1mm. I haven't tested the 1/8" glass but assume it wont work well, usually IR reflections from the top surface of the glass bounce back.
Using something like a Qprox QT1081 touch sensor IC( or similar newer variants), you have to be careful putting signals near the copper plane connected to sensor ICs so I am assuming IR is the best method. I can print the solid black ink and leave a small circle open for an IR sensor on the back to look through assuming something will work in 1/8" clear glass. Radar, Ping, laser TOF, RF all seem problematic. I will have a Prop1 on the PCB on the glass with lots of free pins. Ideally, an off the shelf small diameter IR sensor would be great. Small as in 3/8" diameter clear circle on the glass(no ink), mount the sensor behind the glass.
Any suggestions appreciated. 
Comments
This is the APDS-9960, works great with thin overlay, not with thick material.
I found something very interesting on Digikey. Mentions working through glass, even "smudged" glass. Minimum detection 10mm. Max 330cm.
"If a cover glass is used, the crosstalk calibration is needed also". No mention yet of how many reads per second, still looking. Also no mention of glass thickness, only that it works through cover glass.
Great form factor, very small. I2C.
file:///Users/newowner/Downloads/vl53l3cx.pdf
You might want to checkout the Si labs Si1153
Thanks DigitalBob. I looked at it and will give it more thought, it is certainly in the family of sensors used with overlays.
The family of ST sensors includes one that is better(simpler) suited to my goal which also includes working through glass.
https://www.pololu.com/file/0J961/VL6180X.pdf
This is a time of flight short range LIDAR type plus ambient light sensor designed for touch screens. There are a lot of registers to study, but conveniently someone has already uploaded SPIN files to P1 Github! I will order the eval boards for this and try it out this week.
My friends made this zombie hand scanner, it uses the Qtouch chips from memory
https://www.thekoshertonystark.com/project/zombie-infection-scanner/
I think the optical distance scanner should work fine too. Some of the more recent models have multi-target detection, where they can ignore the first reflection
I have been following this post, a great project.
We need keypads, and all kinds of HMI devices to compete with China products. I sincerely hope you expand on this product line and bring it to market.
As an aside, I have made it a top priority to use only USA designed & manufactured component parts ( alternately NOT made in CHINA ) in all my electronic designs. IMHO, when Taiwan goes, so does all, (or most), of the stuff we buy every day... Beyond scary.