Touch Sensor Module

Since Origin / Contributor Maintainer Source
2019-07-20 ChiliPeppr John Lauer touch.c

The touch sensor module enables you to easily interact with ESP32's built-in 10 touch sensors. The touch pad sensing process is under the control of a hardware-implemented finite-state machine (FSM) which is initiated by software (polling mode) or a dedicated hardware timer (interrupt mode). By using the interrupt mode you can offload the sensing away from the main CPU. There are several examples in the docs below on how to implement your code.

For further information please refer to the ESP-IDF docs for Touch Sensor https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/peripherals/touch_pad.html

Click the YouTube video below for a tutorial on how to use this touch library including sample touch sensors, how to set your touch counter thresholds, and what the touch counters look like in the touched/untouched state of a sensor pad.

YouTube Touch Tutorial

The touch sensors are on the following GPIO pins

Touch Pad Number GPIO Touch Pad Number GPIO
0 GPIO4 5 GPIO12
1 GPIO0 6 GPIO14
2 GPIO2 7 GPIO27
3 GPIO15 8 GPIO33
4 GPIO13 9 GPIO32

Example Lua Code

Example code showing how to configure 8 pads. - Main run file touch_8pads_showlist_test.lua - Library touch_8pads_showlist.lua

Example code showing how to use 5 touch pads to jog a stepper motor at different frequencies depending on which pad is touched: - Main run file touchjog_main.lua - Library touchjog_touch.lua - Library touchjog_jog.lua - Library touchjog_jog_drv8825.lua

touch.create()

Create the touch sensor object. You must call this method first. Only one touch object may be created since most settings on the touch driver are global in nature such as threshold trigger mode, interrupt callbacks, and reference voltages.

Syntax

tp = touch.create({
  pad = 0 || {0,1,2,3,4,5,6,7,8,9}, -- 0=GPIO4, 1=GPIO0, 2=GPIO2, 3=GPIO15, 4=GPIO13, 5=GPIO12, 6=GPIO14, 7=GPIO27, 8=GPIO33, 9=GPIO32
  cb = yourFunc, -- Callback on interrupt
  intrInitAtStart = true || false, -- Turn on/off interrupt at start.
  thres = 0..65536, -- All pads set to this thres. 
  thresTrigger = touch.TOUCH_TRIGGER_BELOW || touch.TOUCH_TRIGGER_ABOVE,
  filterMs = 0..4294967295 -- Filter is only available in polling mode. 
  lvolt = touch.TOUCH_LVOLT_0V4 || touch.TOUCH_LVOLT_0V5 || touch.TOUCH_LVOLT_0V6 || touch.TOUCH_LVOLT_0V7,
  hvolt = touch.TOUCH_HVOLT_2V4 || touch.TOUCH_HVOLT_2V5 || touch.TOUCH_HVOLT_2V6 || touch.TOUCH_HVOLT_2V7, 
  atten = touch.TOUCH_HVOLT_ATTEN_0V || touch.TOUCH_HVOLT_ATTEN_0V5 || touch.TOUCH_HVOLT_ATTEN_1V || touch.TOUCH_HVOLT_ATTEN_1V5 
  isDebug = true || false
})

Parameters

List of values for configuration table:

  • pad Required. padNum || {table of padNums}. Specify one pad like pad = 4, or provide a table list of pads. For example use pad = {0,1,2,3,4,5,6,7,8,9} to specify all pads. Pads allowed are 0=GPIO4, 1=GPIO0, 2=GPIO2, 3=GPIO15, 4=GPIO13, 5=GPIO12, 6=GPIO14, 7=GPIO27, 8=GPIO33, 9=GPIO32.
  • cb Optional. Your Lua method that gets called on touch event. myfunction(pads) will be called where pads is a table of pads that were touched. The key is the pad number while the value is true, i.e. pads = {[2]=true, [3]=true} if pad 2 and 3 were both touched at the same time. When you specify a callback, interrupt mode is automatically turned on. You can specify intrInitAtState = false to manually turn on the interrupt later. If no callback is provided or nil is specified, then polling mode is active where you must call tp:read() to get the touch pad values.
  • intrInitAtStart Optional. Defaults to true. Turn on interrupt at start. Set to false to if you want to configure the touch sensors first and then manually turn on interrupts later with tp:intrEnable().
  • thres Optional. Defaults to 0. Range is 0 to 65536. Provide a threshold value to be set on all pads specified in the pad parameter. Typically you will set thresholds per pad since pad size/shape/wire legnth influences the counter value per pad and thus your threshold is usually differnt per pad. You can set thres later per pad with tp:setThres(padNum, thres).
  • thresTrigger Optional. Defaults to touch.TOUCH_TRIGGER_BELOW.
  • touch.TOUCH_TRIGGER_BELOW
  • touch.TOUCH_TRIGGER_ABOVE
  • filterMs Optional. Range is 0 to 4294967295 milliseconds. Used in polling mode only (if you provide a callback polling mode is disabled). Will filter noise for this many ms to give more consistent counter results. When filterMs is specified you will receive a 2nd return value in the raw, filter = tp:read() call with the filtered values in a Lua table.
  • lvolt Optional. Low reference voltage
  • touch.TOUCH_LVOLT_0V4
  • touch.TOUCH_LVOLT_0V5
  • touch.TOUCH_LVOLT_0V6
  • touch.TOUCH_LVOLT_0V7
  • hvolt Optional. High reference voltage
  • touch.TOUCH_HVOLT_2V4
  • touch.TOUCH_HVOLT_2V5
  • touch.TOUCH_HVOLT_2V6
  • touch.TOUCH_HVOLT_2V7
  • atten Optional. High reference voltage attenuation
  • touch.TOUCH_HVOLT_ATTEN_0V
  • touch.TOUCH_HVOLT_ATTEN_0V5
  • touch.TOUCH_HVOLT_ATTEN_1V
  • touch.TOUCH_HVOLT_ATTEN_1V5
  • isDebug Optional. Defaults to false. Set to true to get debug information during development. The info returned while debug is on can be very helpful in understanding polling vs interrupts, configuration, and threshold settings. Set to false during production.

Returns

touch object

Example 1 - Polling

-- Touch sensor with 5 touch pads for polling counter state

tp = touch.create({
  pad = {0,1,2,3,4}, -- pad = 0 || {0,1,2,3,4,5,6,7,8,9} 0=GPIO4, 1=GPIO0, 2=GPIO2, 3=GPIO15, 4=GPIO13, 5=GPIO12, 6=GPIO14, 7=GPIO27, 8=GPIO33, 9=GPIO32
  lvolt = touch.TOUCH_LVOLT_0V5, -- Low ref voltage TOUCH_LVOLT_0V4, TOUCH_LVOLT_0V5, TOUCH_LVOLT_0V6, TOUCH_LVOLT_0V7 
  hvolt = touch.TOUCH_HVOLT_2V7, -- High ref voltage TOUCH_HVOLT_2V4, TOUCH_HVOLT_2V5, TOUCH_HVOLT_2V6, TOUCH_HVOLT_2V7
  atten = touch.TOUCH_HVOLT_ATTEN_1V, -- High ref attenuation TOUCH_HVOLT_ATTEN_0V, TOUCH_HVOLT_ATTEN_0V5, TOUCH_HVOLT_ATTEN_1V, TOUCH_HVOLT_ATTEN_1V5 
  isDebug = true
})

function read()
  raw = tp:read()
  print("Pad", "RawVal")
  for key, value in pairs(raw) do
    print(key, value)
  end
end

read()

Example 2 - Polling with Filtering

-- Touch sensor with 3 touch pads for polling with filtering

tp = touch.create({
  pad = {4,5,6}, -- pad = 0 || {0,1,2,3,4,5,6,7,8,9} 0=GPIO4, 1=GPIO0, 2=GPIO2, 3=GPIO15, 4=GPIO13, 5=GPIO12, 6=GPIO14, 7=GPIO27, 8=GPIO33, 9=GPIO32
  filterMs = 20, -- Polling mode only. Will filter noise for this many ms to give more consistent counter.
  lvolt = touch.TOUCH_LVOLT_0V5, -- Low ref voltage TOUCH_LVOLT_0V4, TOUCH_LVOLT_0V5, TOUCH_LVOLT_0V6, TOUCH_LVOLT_0V7 
  hvolt = touch.TOUCH_HVOLT_2V7, -- High ref voltage TOUCH_HVOLT_2V4, TOUCH_HVOLT_2V5, TOUCH_HVOLT_2V6, TOUCH_HVOLT_2V7
  atten = touch.TOUCH_HVOLT_ATTEN_1V, -- High ref attenuation TOUCH_HVOLT_ATTEN_0V, TOUCH_HVOLT_ATTEN_0V5, TOUCH_HVOLT_ATTEN_1V, TOUCH_HVOLT_ATTEN_1V5 
  isDebug = true
})

-- You will get 2 parameters from tp:read() when filterMs is specified in create()
function read()
  raw, filter = tp:read()
  -- Use sjson to make pretty output
  print("Touch raw:", sjson.encode(raw))
  print("Touch filt:", sjson.encode(filter))
end

-- Filtered vals will be similar to raw vals on first read.
read()
-- Read a second later to see how filtered vals are more stable.
tmr.create():alarm(1000, tmr.ALARM_SINGLE, read)

Example 3 - Interrupt Touch / Untouch

-- Touch sensor with 1 pad for touch / untouch using threshold trigger mode
-- Swap TOUCH_TRIGGER_BELOW / TOUCH_TRIGGER_ABOVE on each callback
-- NOTE: Can only use this technique with 1 pad

pad = 6 -- 6=GPIO14

padState = 0 -- 0 means untouched
tp = nil -- Holds our touch sensor object

function onTouch(pads)

  if padState == 0 then
    -- we just got touched
    -- swap trigger mode to TOUCH_TRIGGER_ABOVE so we get interrupt
    -- on untouch
    padState = 1
    tp:setTriggerMode(touch.TOUCH_TRIGGER_ABOVE)
    print("Touch")
  else
    -- we just got untouched
    -- swap trigger mode to TOUCH_TRIGGER_BELOW so we get interrupt
    -- on touch
    padState = 0
    tp:setTriggerMode(touch.TOUCH_TRIGGER_BELOW)
    print("Untouch")
  end

end

function init()
  tp = touch.create({
    pad = pad, -- pad = 0 || {0,1,2,3,4,5,6,7,8,9} 0=GPIO4, 1=GPIO0, 2=GPIO2, 3=GPIO15, 4=GPIO13, 5=GPIO12, 6=GPIO14, 7=GPIO27, 8=GPIO33, 9=GPIO32
    cb = onTouch, -- Callback will get Lua table of pads/bool(true) that were touched.
    intrInitAtStart = false, -- Turn on interrupt at start. Default to true. Set to false to config first. Turn on later with tp:intrEnable()
    thresTrigger = touch.TOUCH_TRIGGER_BELOW, -- TOUCH_TRIGGER_BELOW or TOUCH_TRIGGER_ABOVE. Touch interrupt happens if ctr value is below or above.  
    lvolt = touch.TOUCH_LVOLT_0V5, -- Low ref voltage TOUCH_LVOLT_0V4, TOUCH_LVOLT_0V5, TOUCH_LVOLT_0V6, TOUCH_LVOLT_0V7 
    hvolt = touch.TOUCH_HVOLT_2V7, -- High ref voltage TOUCH_HVOLT_2V4, TOUCH_HVOLT_2V5, TOUCH_HVOLT_2V6, TOUCH_HVOLT_2V7
    atten = touch.TOUCH_HVOLT_ATTEN_1V, -- High ref attenuation TOUCH_HVOLT_ATTEN_0V, TOUCH_HVOLT_ATTEN_0V5, TOUCH_HVOLT_ATTEN_1V, TOUCH_HVOLT_ATTEN_1V5 
    isDebug = true
  })

end

function read()
  local raw = tp:read()
  print("Pad", "Val")
  for key,value in pairs(raw) do 
    print(key,value) 
  end
end

-- Do not touch during config
function config()
  local raw = tp:read()
  -- set threshold to 20% of baseline read state
  local thres = raw[pad] - math.floor(raw[pad] * 0.2)
  tp:setThres(pad, thres)
  print("Pad is at " .. raw[pad] .. " when not touched")
  print("Will trigger at thres: " .. thres)
  tp:intrEnable()
end

init()
read()
config()

Example 4 - Interrupt Touch / Untouch with Timer

-- Touch sensor with 1 pad for touch / untouch using timer
-- Shows how to detect a touch and then an untouch

m = {}

m.pad = {8} -- 8=GPIO33

m._tp = nil -- will hold the touchpad obj
m._padState = 0 -- 0 means untouched
m._tmr = nil -- will hold the tmr obj
m._tmrWait = 50 -- ms to wait for no callback to indicate untouch

-- We will get a callback every 8ms or so when touched
-- We will reset the tmr each time and after 50ms will presume untouched event
function m.onTouch(pads)

  if m._padState == 0 then
    -- we just got touched
    m._padState = 1 -- 1 means touched
    m._tmr:start()
    print("Touch")
  else -- m._padState == 1
    -- we will get here on successive callbacks while touched
    -- we get them about every 8ms
    -- reset the tmr so it doesn't timeout yet
    m._tmr:stop()
    m._tmr:start()
  end

end

function m.onTmr()
  -- if we get the timer triggered, it means that we timed out
  -- from touch callbacks, so we presume the touch ended
  m._padState = 0
  print("Untouch")
end

function m.init()
  m._tp = touch.create({
    pad = m.pad, -- pad = 0 || {0,1,2,3,4,5,6,7,8,9} 0=GPIO4, 1=GPIO0, 2=GPIO2, 3=GPIO15, 4=GPIO13, 5=GPIO12, 6=GPIO14, 7=GPIO27, 8=GPIO33, 9=GPIO32
    cb = m.onTouch, -- Callback will get Lua table of pads/bool(true) that were touched.
    intrInitAtStart = false, -- Turn on interrupt at start. Default to true. Set to false in case you want to config first. Turn it on later with tp:intrEnable()
    thresTrigger = touch.TOUCH_TRIGGER_BELOW, -- TOUCH_TRIGGER_BELOW or TOUCH_TRIGGER_ABOVE. Touch interrupt will happen if counter value is below or above threshold.  
    lvolt = touch.TOUCH_LVOLT_0V5, -- Low ref voltage TOUCH_LVOLT_0V4, TOUCH_LVOLT_0V5, TOUCH_LVOLT_0V6, TOUCH_LVOLT_0V7 
    hvolt = touch.TOUCH_HVOLT_2V7, -- High ref voltage TOUCH_HVOLT_2V4, TOUCH_HVOLT_2V5, TOUCH_HVOLT_2V6, TOUCH_HVOLT_2V7
    atten = touch.TOUCH_HVOLT_ATTEN_1V, -- High ref attenuation TOUCH_HVOLT_ATTEN_0V, TOUCH_HVOLT_ATTEN_0V5, TOUCH_HVOLT_ATTEN_1V, TOUCH_HVOLT_ATTEN_1V5 
    isDebug = true
  })

  -- Setup the tmr for the callback process
  m._tmr = tmr.create()
  m._tmr:register(m._tmrWait, tmr.ALARM_SEMI, m.onTmr)

end

function m.read()
  local raw = m._tp:read()
  print("Pad", "Val")
  for key,value in pairs(raw) do 
    print(key,value) 
  end
end

-- Do not touch pad during config
function m.config()
  local raw = m._tp:read()
  -- set threshold to 20% of baseline read state
  local thres = raw[m.pad] - math.floor(raw[m.pad] * 0.2)
  m._tp:setThres(m.pad, thres)
  print("Pad is at ", raw[m.pad], " as baseline")
  print("Will trigger at thres: ", thres)
  m._tp:intrEnable()
end

m.init()
m.read()
m.config()

touchObj:read()

Read the touch sensor counter values for all pads configured in touch.create() method.

Syntax

raw, filter = tp:read()

Parameters

None

Returns

  • raw Lua table of touch sensor counter values per pad
  • raw, filter A 2nd Lua table of touch sensor filtered counter values per pad is returned if filterMs is specified during the touch.create() method.

Example 1 - Raw

raw = tp:read()
print("Pad", "Val")
for key,value in pairs(raw) do 
  print(key,value) 
end

Example 2 - Raw / Filter

-- You get a filter Lua table if you specified filterMs in touch.create()
raw, filter = tp:read()
print("Pad", "Raw", "Filt")
print("---", "---", "----")
for key,value in pairs(raw) do 
  print(key,value,filter[key]) 
end

touchObj:setThres(padNum, thresVal)

Set touch sensor interrupt threshold per pad. The threshold only matters if you are in interrupt mode, which only activates if you specify a callback in the touch.create() configuration.

Syntax

tp:setThres(padNum, thresVal)

Parameters

  • padNum Required. One pad number can be specified here. If you did multiple pads you must call this per pad.
  • thresVal Required. The threshold value to set for the pad interrupt trigger. If you set touch.TOUCH_TRIGGER_BELOW then the interrupt occurs when the touch counter goes below this threshold value, or vice versa for touch.TOUCH_TRIGGER_ABOVE.

Returns

nil

Example 1

-- Set threshold for pad 2 where baseline counter is around 800 and 
-- when touched is around 200, so trigger at mid-point around 500
tp:setThres(2, 500)

Example 2

-- Configure by reading baseline, then setting threshold to 30% below base
local raw = tp:read()
print("Pad", "Base", "Thres")
for key,value in pairs(raw) do 
  if key ~= nil then
    -- reduce by 30%
    local thres = raw[key] - math.floor(raw[key] * 0.3)
    tp:setThres(key, thres)
    print(key, value, thres) 
  end
end
-- Now enable interrupts since our thresholds are correct
tp:intrEnable()

touchObj:setTriggerMode()

Set the trigger mode globally for all touch pads. The trigger mode only matters in interrupt mode where you can tell the hardware to give you an interrupt if the counter on the pad falls above or below the threshold you specify.

Syntax

tp:setTriggerMode(mode)

Parameters

  • mode Required. touch.TOUCH_TRIGGER_BELOW or touch.TOUCH_TRIGGER_ABOVE can be specified. If your pad's baseline counter value is around 600 when not touched, and sits around 300 when touched, then you would set your threshold around 450. If you set touch.TOUCH_TRIGGER_BELOW then when the counter drops to 300 it would fall BELOW the threshold of 450, thus triggering the interrupt. This process works in the reverse for touch.TOUCH_TRIGGER_ABOVE.

Returns

nil

Example 1

-- Trigger callback when pad counter goes above threshold value
tp:setTriggerMode(touch.TOUCH_TRIGGER_ABOVE)
-- Trigger callback when pad counter goes below threshold value
tp:setTriggerMode(touch.TOUCH_TRIGGER_BELOW)

Example 2

-- Configure touch hardware to callback on TOUCH_TRIGGER_BELOW during touch.create()
-- Then on first callback swap to TOUCH_TRIGGER_ABOVE when detecting touch
-- Then will get 2nd callback on untouch due to mode change
-- This only works with 1 pad since trigger mode is global for all pads

padState = 0 -- Set start padState

function onTouch(pads)

  if padState == 0 then
    -- we just got touched
    -- swap trigger mode to TOUCH_TRIGGER_ABOVE so we get interrupt
    -- on untouch
    padState = 1
    tp:setTriggerMode(touch.TOUCH_TRIGGER_ABOVE)
    print("Got touch")
  else
    -- we just got untouched
    -- swap trigger mode to TOUCH_TRIGGER_BELOW so we get interrupt
    -- on touch
    padState = 0
    tp:setTriggerMode(touch.TOUCH_TRIGGER_BELOW)
    print("Got untouch")
  end

  print("Pads:", sjson.encode(pads))

end

touchObj:intrEnable()

Enable interrupt on the touch sensor hardware. You can specify intrInitAtStart=false during touch.create() and thus you would want to call this method later on after configuring your pad thresholds.

Syntax

tp:intrEnable()

Parameters

None

Returns

nil

Example

tp:intrEnable() -- Enable interrupt

touchObj:intrDisable()

Disable interrupt on the touch sensor hardware.

Syntax

tp:intrDisable()

Parameters

None

Returns

nil

Example

tp:intrDisable() -- Disable interrupt