Week 11. input devices
Assignment
- group project: measure the analog levels and digital signals in an input device
- measure something: add a sensor to a microcontroller board that you have designed and read it.
group assignment
see FabLab Kamakura's group assignment page.
temperature sensor via SPI interface
I need a temperature sensor with my surFABoard to measure seawater temperature. Neil's example was one for ambient temperature and not suitable for my purpose. So, I decided to use K-type thermocouple converter, MAX6675 (and MAX31855, eventually).
I tried to design a knockoff MAX6675 module and combine it with ATtiny45 with reference to this circuit.
board design/production
MAX6675 connects with a microprocessor through SPI interface. As I couldn't find an example for SPI interface in Fab Academy archive, I designed it with reference to a MAX6675 breakout board.
Eagle schematic/PCB layout and toolpathes for traces/interior: archived format (.zip)
making my board Arduino compatible
problem#1: burning bootloading error
I want to use my board as an Arduino compatible. I tried to burn bootloader, but I've got an error message saying...
Arduino: 1.8.5 (Mac OS X), Board: "ATtiny25/45/85, ATtiny45, Internal 8 MHz"
/Applications/Arduino.app/Contents/Java/hardware/tools/avr/bin/avrdude -C/Applications/Arduino.app/Contents/Java/hardware/tools/avr/etc/avrdude.conf -v -v -v -v -pattiny45 -cusbtiny -e -Uefuse:w:0xff:m -Uhfuse:w:0xdf:m -Ulfuse:w:0xe2:m
avrdude: Version 6.3, compiled on Jan 17 2017 at 12:01:35
Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
Copyright (c) 2007-2014 Joerg Wunsch
System wide configuration file is "/Applications/Arduino.app/Contents/Java/hardware/tools/avr/etc/avrdude.conf"
User configuration file is "/Users/kwhrjn/.avrduderc"
User configuration file does not exist or is not a regular file, skipping
Using Port : usb
Using Programmer : usbtiny
avrdude: usbdev_open(): Found USBtinyISP, bus:device: 020:045
AVR Part : ATtiny45
Chip Erase delay : 4500 us
PAGEL : P00
BS2 : P00
RESET disposition : possible i/o
RETRY pulse : SCK
serial program mode : yes
parallel program mode : yes
Timeout : 200
StabDelay : 100
CmdexeDelay : 25
SyncLoops : 32
ByteDelay : 0
PollIndex : 3
PollValue : 0x53
Memory Detail :
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
----------- ---- ----- ----- ---- ------ ------ ---- ------ ----- ----- ---------
eeprom 65 6 4 0 no 256 4 0 4000 4500 0xff 0xff
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
----------- ---- ----- ----- ---- ------ ------ ---- ------ ----- ----- ---------
flash 65 6 32 0 yes 4096 64 64 4500 4500 0xff 0xff
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
----------- ---- ----- ----- ---- ------ ------ ---- ------ ----- ----- ---------
signature 0 0 0 0 no 3 0 0 0 0 0x00 0x00
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
----------- ---- ----- ----- ---- ------ ------ ---- ------ ----- ----- ---------
lock 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
----------- ---- ----- ----- ---- ------ ------ ---- ------ ----- ----- ---------
lfuse 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
----------- ---- ----- ----- ---- ------ ------ ---- ------ ----- ----- ---------
hfuse 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
----------- ---- ----- ----- ---- ------ ------ ---- ------ ----- ----- ---------
efuse 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
----------- ---- ----- ----- ---- ------ ------ ---- ------ ----- ----- ---------
calibration 0 0 0 0 no 1 0 0 0 0 0x00 0x00
Programmer Type : USBtiny
Description : USBtiny simple USB programmer, http://www.ladyada.net/make/usbtinyisp/
avrdude: programmer operation not supported
avrdude: Using SCK period of 10 usec
CMD: [ac 53 00 00] [ff ff ff ff]
CMD: [ac 53 00 00] [ff ff ff ff]
avrdude: initialization failed, rc=-1
Double check connections and try again, or use -F to override
this check.
avrdude done. Thank you.
Error while burning bootloader.Yamamoto-san, a FabLab Kamakura's electronics GURU, said that a CS (Chip Select) pin should be pulled up with a resistor. Otherwise, the pin would be floating state, which might cause the bootloading error.
After I soldered a 10K pull-up resistor as he said, I could burn bootloader.
arduino sketch
problem#2: Chip Select pin remaining HIGH
I used a MAX6675 library and modified an example sketch to use serial monitor.
After loading my sketch, temperature sensor reading was 0 degree in Celsius, which meant it's not working...
One of the reasons I found was that CS pin should be LOW state while reading a data from MAX6675 via MISO, but CS remained HIGH state.
I checked my circuit schematic and wiring over and over, but I couldn't find the reason why.
breadboard test
To test my board more flexible, I reconfigured my design onto a breadboard. I used SOP-DIP breakout board for ATtiny45 and MAX6675.
Sadly, the test result was the same, CS stayed HIGH and the zero reading.
I removed a MAX6675 chip and uploaded a simple sketch to monitor whether CS state could change its state. I could check ATtiny was working properly.
I decided to ditch MAX6675 and use a MAX31855 breakout board (adafruit) instead.
problem#3: ATtiny45 doesn't support SPI.h
I tested ATtiny45 with MAX31855 breakout board on a breadboard.
I used a MAX31855 library and modified an example sketch. I tried to compile it but I couldn't. MAX31855 library includes SPI library, but the problem was that ATtiny didn't support it.
problem#4: memory map difference
I went back to a MAX6675 library. I thought I might be able to use MAX 6675 library with MAX31855 chip because they seemed to be same difference to me.
The result was a sort of successful but not perfect. Thermocouple sensor sent back a sort of reading data, but it's not stable at all. Reading data changed between a sort of proper value and nan(no data) intermittently.
I delved into their datasheets (MAX6675, MAX31855) and what I found (with significant support from Yamamoto-san, again) were that MAX31855 and MAX6675 had different memory maps. MAX31855 and MAX6675 send back 32 bits and 16 bits data, respectively. MAX31855 has 14-bit temperature data and, MAX6675 has 12-bit.
In MAX6675's library, a function dealt with 16-bit data, so I modified to be able to deal with 32-bit data for MAX31855. In addition to that, I used bit shift "V >>= 2" to ignore D17/D16 and read 14-bit temperature data (from D31 to D18).
Originally in case MAX6675 "v >>= 3" ignores from D2 to D0 to read 12-bit temperature reading( D14 to D3 ).
double MAX6675::readCelsius(void) {
uint16_t v;
uint16_t v1; //added
digitalWrite(cs, LOW);
_delay_ms(1);
v = spiread();
v <<= 8;
v |= spiread();
v1 = spiread(); //added
v1 <<=8; //to read
v1 |= spiread(); //lower 16bits
digitalWrite(cs, HIGH);
if (v & 0x1) { //modified from "if (v & 0x4)"
// uh oh, no thermocouple attached!
return NAN;
//return -100;
}
v >>= 2; //modified from "v >>= 3;"
return v*0.25;
}
Now I've got proper readings!!!
my ATtiny board and commercial MAX31855 breakout board
I redesigned circuit schematic to put a pull-up resistor, milled a PCB and soldered all componemts. I connected it with MAX31855 breakout board via SPI interface.
And here is the hero shot.
I could read the temperature from oscilloscope! Yellow wave was SCK, and blue wave was MISO.
files
ATtiny45 with MAX6675 board (Eagle schematic/PCB layout; toolpaths for traces/interior): archived format (.zip)
modified attiny board : archive format (.zip)
modified MAX6675 libraries: archived format (.zip)
Arduino sketch: Arduino IDE format (.ino)