Unfortunately, I dont have that many options to work with. My friend casted a lot of faces before he came up with the idea of making them play audio. And since they are concrete, we cant drill into them to add some form of button(could crack them). So I have to use capacitive touch in proximity mode.
Don't you still have to drill them, or is the touch sensor on top?
Don't you still have to drill them, or is the touch sensor on top?
No, we can't drill the castings. The sensor would be on the back of each face. Not looking for persision, just when someone places there hand on a face, the sensor chip will detect it
How are you attaching the touch pad to the faces? Perhaps it could be made larger to increase the change in capacitance.
I was thinking of trying epoxy first, to see how well it sticks. But as a last resort, using tapcons to hold abs plastic sheets that have foil tape on them to act as the proximity sensor. I have done some work with aluminum foil, I can get the sensor chip to detect my hand over 12 inches away, using a 6" x 6" piece of foil. But that is not accounting for 3"-4" of concrete.
Epoxy or PLPremium should be fine for holding aluminum foil on the back of each face. I wonder if using a cmos 555 timer as an oscillator/driver on each face would work better. The propeller could detect the change in frequency when a hand is placed on the face.
Epoxy or PLPremium should be fine for holding aluminum foil on the back of each face. I wonder if using a cmos 555 timer as an oscillator/driver on each face would work better. The propeller could detect the change in frequency when a hand is placed on the face.
The main issue I am worried about is how long this art project will be up and running. My friend is saying he would like to put it in a local park, and for it to be up for a few years. I am worried about how the capacitance changes over time, and with temperature. That is the only reason I want to use a chip that is designed for touch sensing. It can calibrate it self, the prop doesn't have to do a thing.
Epoxy or PLPremium should be fine for holding aluminum foil on the back of each face. I wonder if using a cmos 555 timer as an oscillator/driver on each face would work better. The propeller could detect the change in frequency when a hand is placed on the face.
The main issue I am worried about is how long this art project will be up and running. My friend is saying he would like to put it in a local park, and for it to be up for a few years. I am worried about how the capacitance changes over time, and with temperature. That is the only reason I want to use a chip that is designed for touch sensing. It can calibrate it self, the prop doesn't have to do a thing.
If you can get the CAP to work for your application that is definitely the way to go.
On the other hand the 555 timer is a very rugged and reliable chip and you could probably connect as many as 24 or 25 of them to a single propeller with only one signal wire for each face, so 40 to 42 rather than 125 chips for 1000 touch sensors. Since putting a hand on the face will result in an immediate change in frequency the software can self calibrate for frequency drift by keeping a longer term average frequency to compare to each single reading.
This chip is not that bad. Simple, and looks like it would do a good job. But a couple down sides I can see.
1) It needs a external capacitor (CPC) to set the sensitivity. That would be fine if the area in front of the sensor was the same, like a panel or something. But these faces have a different thickness from face to face. It would be impossible to change the capacitor in the field, by an artist, not an electronics guy.
2) The cost would be higher then using the CAP1188. 1000 chips * $0.705 (each chip) = $705 for the PCF8883T, compared to, 125 chips (125 chips * 8 channels) * $0.93 = $116.25 for the CAP1188
This is a nice chip. Little strange on what it needs to work though... from the datasheet
the FDC2112, FDC2114, FDC2212, and FDC2214 employ an L-C resonator, also known as L-C
tank, as a sensor.
So this chip needs a L-C circuit to work?! I think that could be a little over board for this setup. Plus the cost would be horrible. 250 chips (250 chips * 4 channels) * $4.97 = $1242.50
I really do appreciate the options though. It is a challenge trying to design this by myself, and I am glad I have everyone on here to brainstorm with.
Comments
No, we can't drill the castings. The sensor would be on the back of each face. Not looking for persision, just when someone places there hand on a face, the sensor chip will detect it
I was thinking of trying epoxy first, to see how well it sticks. But as a last resort, using tapcons to hold abs plastic sheets that have foil tape on them to act as the proximity sensor. I have done some work with aluminum foil, I can get the sensor chip to detect my hand over 12 inches away, using a 6" x 6" piece of foil. But that is not accounting for 3"-4" of concrete.
The main issue I am worried about is how long this art project will be up and running. My friend is saying he would like to put it in a local park, and for it to be up for a few years. I am worried about how the capacitance changes over time, and with temperature. That is the only reason I want to use a chip that is designed for touch sensing. It can calibrate it self, the prop doesn't have to do a thing.
If you can get the CAP to work for your application that is definitely the way to go.
On the other hand the 555 timer is a very rugged and reliable chip and you could probably connect as many as 24 or 25 of them to a single propeller with only one signal wire for each face, so 40 to 42 rather than 125 chips for 1000 touch sensors. Since putting a hand on the face will result in an immediate change in frequency the software can self calibrate for frequency drift by keeping a longer term average frequency to compare to each single reading.
http://www.mouser.com/ProductDetail/NXP-Semiconductors/PCF8883T-1118/?qs=sGAEpiMZZMs3uAJYYmvlKwtKN4fpBO8yzeonQ6OxnV4=
4channel (new product)
http://www.mouser.com/ProductDetail/Texas-Instruments/FDC2114QRGHTQ1/?qs=sGAEpiMZZMs3uAJYYmvlKzJTNoqGYBBPT9vkJFvF4qijBQC4BecaDA==
This chip is not that bad. Simple, and looks like it would do a good job. But a couple down sides I can see.
1) It needs a external capacitor (CPC) to set the sensitivity. That would be fine if the area in front of the sensor was the same, like a panel or something. But these faces have a different thickness from face to face. It would be impossible to change the capacitor in the field, by an artist, not an electronics guy.
2) The cost would be higher then using the CAP1188. 1000 chips * $0.705 (each chip) = $705 for the PCF8883T, compared to, 125 chips (125 chips * 8 channels) * $0.93 = $116.25 for the CAP1188
This is a nice chip. Little strange on what it needs to work though... from the datasheet
So this chip needs a L-C circuit to work?! I think that could be a little over board for this setup. Plus the cost would be horrible. 250 chips (250 chips * 4 channels) * $4.97 = $1242.50
I really do appreciate the options though. It is a challenge trying to design this by myself, and I am glad I have everyone on here to brainstorm with.
TC