A walkthrough of how to write a driver for a gesture sensor integrated circuit in JavaScript running on Tessel. Full driver is here: https://github.com/jiahuang/apds-gesture

1. JS Gesture Sensor Driver
@jia | Jia Huang | co-founder & developer Technical Machine

2. Tessel is a WiFi-enabled microcontroller
that runs JavaScript.

4. Gesture
sensor
+
Tessel DIY
module

7. ???

8. Sensor block diagram

9. Sensor block diagram
some
stuff

10. Sensor block diagram
some
stuff

11. Hardware communication busses
I2C SPI UAR
T

12. I2C
I2C{SC
L
SDA

13. I2C
I2C{SC
L
SDA
Clock
Data

14. I2C
I2C{SC
L
SDA
Clock
Data

15. I2C
I2C{SC
L
SDA
Clock
Data
binary 0 1 0 0 0 0 0 1 0

16. I2C
I2C{SC
L
SDA
Clock
Data
binary 0 1 0 0 0 0 0 1 0
= 0x42

17. I2C
I2C{SC
L
SDA
Clock
Data
binary 0 1 0 0 0 0 0 1 0
= 0x42WRONG

18. The devices support
the 7-bit I2C-bus
addressing protocol.
(datasheet pg 8 … out of 38)
RTFM

19. I2C
I2C{SC
L
SDA
Clock
Data
binary 0 1 0 0 0 0 0 1 0
MS
B
0 = write
1 = read
ACK

20. I2C
I2C{SC
L
SDA
Clock
Data
binary 0 1 0 0 0 0 0 1 0
MS
B
0 = write
1 = read
ACK

21. I2CI2C on Tessel
var i2c = new tessel.port[‘A’].I2C ( address )

22. I2CI2C on Tessel
i2c.send ( txBuffer, callback )
var i2c = new tessel.port[‘A’].I2C ( address )

23. I2CI2C on Tessel
i2c.send ( txBuffer, callback )
i2c.receive ( rxLength, callback )
var i2c = new tessel.port[‘A’].I2C ( address )

24. I2CI2C on Tessel
i2c.send ( txBuffer, callback )
i2c.receive ( rxLength, callback )
i2c.transfer ( txBuffer, rxLength, callback )
var i2c = new tessel.port[‘A’].I2C ( address )

25. I2C
(7 bit addressing)

26. Data?
I2C
(7 bit addressing)

27. ACK ACK ACK
RTFM

28. RTFM
Start 0x39 write
ACK
Register to write Data to write
ACK ACK

29. RTFMRegisters

30. RTFMRegisters

31. RTFMRegisters

32. Values
from
sensor

33. Values
from
sensor
Read these

34. Read these
Values
from
sensor
“host begins to read
0xFC and reads until
the FIFO is empty
(pg 33 of datasheet)

35. How the sensor works

36. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math

37. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math
var tessel = require('tessel');
// 0x39 is device address
var i2c = tessel.port['A’].I2C(0x39);
i2c.transfer(new Buffer([0x92]), 1, function(err, data){
console.log('data', data);
if (data[0] == 0xAB) {
console.log('found a gesture sensor!');
}
});
1
2
3
4
5
6
7
8
9

38. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math
var tessel = require('tessel');
// 0x39 is device address
var i2c = tessel.port['A’].I2C(0x39);
i2c.transfer(new Buffer([0x92]), 1, function(err, data){
console.log('data', data);
if (data[0] == 0xAB) {
console.log('found a gesture sensor!');
}
});
1
2
3
4
5
6
7
8
9

39. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math
Get gesture
direction
● Enable Register (0x80)
● Gesture Proximity Enter Threshold Register (0xA0)
● Gesture Exit Threshold Register (0xA1)
● Gesture Pulse Count and Length Register (0xA6)
● Gesture Control Enable (0xAB)

40. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math
Get gesture
direction
Gesture Status Register (0xAF)
bit # 0 1 2 3 4 5 6 7

41. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math
Gesture Status Register (0xAF)
bit # 0 1 2 3 4 5 6 7
GVALID
(1 = valid data)

42. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math
Gesture Status Register (0xAF)
bit # 0 1 2 3 4 5 6 7
GVALID
(1 = valid data)
GFOV
1 = FIFO overflow

43. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math
Gesture Status Register (0xAF)
bit # 0 1 2 3 4 5 6 7
Reserved
GVALID
(1 = valid data)
GFOV
1 = FIFO overflow

44. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math
Gesture Status Register (0xAF)
bit # 0 1 2 3 4 5 6 7
Reserved
GVALID
(1 = valid data)
GFOV
1 = FIFO overflow
i2c.transfer(new Buffer([0xAF]), 1, function(err, data){
console.log('data', data);
if (data[0] && 1) {
console.log(valid gesture data');
}
});
1
2
3
4
5
6

45. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math
1. Get gesture data size
2. Read 4x amount of gesture data

46. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math
1. Get gesture data size
2. Read 4x amount of gesture data
Gesture FIFO Level Register (0xAE)
Start reading from 0xFC (up dir)

47. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math
1. Get gesture data size
2. Read 4x amount of gesture data
Gesture FIFO Level Register (0xAE)
Start reading from 0xFC (up dir)
i2c.transfer(new Buffer([0xAE]), 1, function(err, fifoLevel){
var fifoLen = fifoLevel[0]*4;
i2c.transfer(new Buffer([0xFC]), fifoLen, function(err, gData){
console.log(’gesture data’, gData);
});
});
1
2
3
4
5
6

48. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math

49. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math
threshold

50. Sensor present?
Enable sensor
Valid gesture?
Read gesture
registers
Math
threshold
start time end time
up_down = (data[up][start_time] - data[down][start_time]) -
(data[up][end_time] - data[down][end_time])
left_right = (data[left][start_time] - data[right][start_time]) -
(data[left][end_time] - data[right][end_time])

51. I2C
Demo?

52. I2C
Questions?
github.com/jiahuang/apds-gesture
@jia | jia@technical.io