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colin
2022-06-30 23:52:28 -07:00
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README.md
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@@ -12,13 +12,13 @@ Foot presses create mechanical waves. Piezoelectrics can turn these waves into v
Method 1b: Surface acoustic waves Method 1b: Surface acoustic waves
--------- ---------
Use a piezoelectric device to insert an acoustic wave onto the pad, and an array of piezos to detect its phase/amplitude at locations along the border. Pressure differences from standing feet will affect the phase/amplitude, and you can create a pressure map of the surface. Use a piezoelectric device to insert an acoustic wave onto the pad, and an array of piezos to detect its phase/amplitude at locations along the border. Pressure differences from standing feet will affect the phase/amplitude, and you can create a pressure map of the surface.
See: https://en.wikipedia.org/wiki/Surface_acoustic_wave_sensor See: <https://en.wikipedia.org/wiki/Surface_acoustic_wave_sensor>
Method 2a: Capacitive displacement sensing Method 2a: Capacitive displacement sensing
--------- ---------
Two parallel conductive plates form a capacitor. If pressure on the top plate deforms it, that changes the capacitance. Measure this and triangulate it to find foot locations. Two parallel conductive plates form a capacitor. If pressure on the top plate deforms it, that changes the capacitance. Measure this and triangulate it to find foot locations.
This is sort of like turning the pad into a giant microphone, but with triangulation. This is sort of like turning the pad into a giant microphone, but with triangulation.
See: https://en.wikipedia.org/wiki/Capacitive_displacement_sensor See: <https://en.wikipedia.org/wiki/Capacitive_displacement_sensor>
WORK SO FAR WORK SO FAR
@@ -26,9 +26,9 @@ WORK SO FAR
Method 1a is demonstrated. It works on rigid surfaces. See doc/data/itm-on-table-drop-30lb-halfway-through.wav: this was achieved using 181.5 clock single-ended ADC sampling with delay(1) between each sample with no external amplification. The piezo was held in place using an empty water glass. Method 1a is demonstrated. It works on rigid surfaces. See doc/data/itm-on-table-drop-30lb-halfway-through.wav: this was achieved using 181.5 clock single-ended ADC sampling with delay(1) between each sample with no external amplification. The piezo was held in place using an empty water glass.
On pad: doc/data/itm-on-pad-heavy-hit-halfway-through.wav demonstrates the same setup on a Polish pad on carpet but with a full glass of water. On pad: <doc/data/itm-on-pad-heavy-hit-halfway-through.wav> demonstrates the same setup on a Polish pad on carpet but with a full glass of water.
doc/data/itm-on-pad-tape-big-hit-4clock-1024buffer.{wav,png} shows what we get with a BIG stomp if the sensor is taped to a pad <doc/data/itm-on-pad-tape-big-hit-4clock-1024buffer.wav> and <doc/data/itm-on-pad-tape-big-hit-4clock-1024buffer.png> shows what we get with a BIG stomp if the sensor is taped to a pad
it's really hard to get. it's really hard to get.
Tried using flat piezos and the L-shaped ones, both behave similarly. Really difficult to get reliable waves. Tried using flat piezos and the L-shaped ones, both behave similarly. Really difficult to get reliable waves.
@@ -40,14 +40,14 @@ Try:
- Borrow UW's oscilloscope - Borrow UW's oscilloscope
- Buy a cheapo scope? - Buy a cheapo scope?
doc/data/itm-sandwich-51medianfilt.png shows results after taping a piezo to a flat surface, loosely setting an acryllic plate on top of it, and then tapping the plate moderately. <doc/data/itm-sandwich-51medianfilt.png> shows results after taping a piezo to a flat surface, loosely setting an acryllic plate on top of it, and then tapping the plate moderately.
There is median filtering on the device side, plus additional filtering on the PC side. There is median filtering on the device side, plus additional filtering on the PC side.
Median filter seems to be key. Even without the plate, the device can _detect_ stomps from 4-5 inches away, though not quite as cleanly. Median filter seems to be key. Even without the plate, the device can _detect_ stomps from 4-5 inches away, though not quite as cleanly.
Placing the piezo such that half of it is in air seems to help detection. I suspect if the whole platform is oscillating, I want the other end of the piezo somewhere that's more fixed, in order to detect the oscillation of the platform itself. Alternatively, I believe a longer piezo element attached all to the surface could help. A smaller element should still receive everything, but the high frequencies are attenuated. Perhaps then, a HPF could be installed to mitigate this attenuation? Placing the piezo such that half of it is in air seems to help detection. I suspect if the whole platform is oscillating, I want the other end of the piezo somewhere that's more fixed, in order to detect the oscillation of the platform itself. Alternatively, I believe a longer piezo element attached all to the surface could help. A smaller element should still receive everything, but the high frequencies are attenuated. Perhaps then, a HPF could be installed to mitigate this attenuation?
Could also try replacing the device-side median filter with a more tuned filter (HPF) Could also try replacing the device-side median filter with a more tuned filter (HPF)
data/itm-pad-drop-weight-3in-away-covered-tape.png: shows clear signal dropping a 30lb weight near the sensor, even when the sensor is fully attached to the pad. Whole signal is about 5 ms. <doc/data/itm-pad-drop-weight-3in-away-covered-tape.png>: shows clear signal dropping a 30lb weight near the sensor, even when the sensor is fully attached to the pad. Whole signal is about 5 ms.
51-median filt device side 51-median filt device side
5000-sample DC removal PC side 5000-sample DC removal PC side
timescale is accurate timescale is accurate
@@ -59,7 +59,7 @@ Resources (acoustic touch screen):
Because of the reflections from the edges of the surface, it's able to work with just one sensor. Because of the reflections from the edges of the surface, it's able to work with just one sensor.
- https://www.elotouch.com/touchscreen-components/catalog-product-view-id-82.html - https://www.elotouch.com/touchscreen-components/catalog-product-view-id-82.html
off-the-shelf SAW touchscreens (for sale?) off-the-shelf SAW touchscreens (for sale?)
- http://a-touch.com.tw/product-saw.htm - <http://a-touch.com.tw/product-saw.htm>
shows how SAW touch screen works (it's like I thought: transmit -> interfere (from finger) -> receive shows how SAW touch screen works (it's like I thought: transmit -> interfere (from finger) -> receive
Resources (using Piezos) Resources (using Piezos)