Initially there was some problem with the pads being too big which was fixed by changing the settings in the design review configuration
I tried experimenting with routing on two layers, but eventually gave up because it’ll probably be obnoxious to flip the board and align it properly. Certainly more complicated than just adding a few zero ohm resistors.
Here is the single layer board layout which I ended up settling on, there are a few changes compared to the “real” first working boards, but almost all the components are in their same places.
The motor is driven by an H-Bridge, the Allegro MicroSystems, LLC A4953ELJTR-T.
David A. Mellis has a arduino ide plugin which adds support for programming ATTinys: https://github.com/damellis/attiny
It has a rigid pin mapping which is incompatible with some libraries.
I’m using SpenceKonde’s ATTinyCore (https://github.com/SpenceKonde/ATTinyCore) which has configurable pinouts
The “Alternative Pinout” corresponds to the ATTinyCore pinout, whereas the normal one is the damellis one.
Grace Copplestone suggested increasing the default on_delay duration from 3us to 30us, which seemed to make it work.
David Mellis has a good tutorial for setting up the Arduino IDE for use with the ATTiny: http://highlowtech.org/?p=1695
But I think ATTinyCore has better features, so I used http://drazzy.com/package_drazzy.com_index.json as the board manager URL instead
I was getting this error trying out the watchdog code from https://github.com/sparkfun/H2OhNo/blob/master/firmware/H2OhNo/H2OhNo.ino
It turns out that according to the datasheets, WDTCR has been renamed to WDTCSR
http://www.nongnu.org/avr-libc/user-manual/group__avr__watchdog.html
wdt_reset()
WDTO_15MS, WDTO_30MS, WDTO_60MS, WDTO_120MS, WDTO_250MS, WDTO_500MS, WDTO_1S, WDTO_2S, WDTO_4S, WDTO_8S
avr/sleep.h: Power Management and Sleep Modes
http://www.nongnu.org/avr-libc/user-manual/group__avr__sleep.html#ga3775b21f297187752bcfc434a541209a
Servos apparently use ~100mA idling with no load, and about 1A in operation according to http://www.rcuniverse.com/forum/rc-radios-transmitters-receivers-servos-gyros-157/2357551-how-much-power-does-servo-use.html
We definitely want to be using /much/ less power than that when idling, so we need some way of switching off the whole servo apparatus.
Apparently the Sevo.detach() method doesn’t actually do anything as most servos are not designed with the case that PWM stops in mind http://www.modsbyus.com/how-to-properly-detachturn-off-a-servo-with-arduino/.
So I think the right thing to do is to have some sort of MOSFET to switch on/off the servo part of the board.
P-Channel MOSFET: https://www.fairchildsemi.com/datasheets/ND/NDS356AP.pdf
When using a MOSFET, you can switch at either the high side (toggling connectivity to power) or low side (toggling connectivity to ground). You would use P-Channel for switching the high side, and N-Channel for switching the low side.
I think if I want to switch 5V with a P-Channel MOSFET, the transition happens around 5V - Vgs, which seems to be about 1.6V
But we’re running the microcontroller at 3.3V, so there’s a good chance we can’t actually switch between the modes.
It looks like we’ll have to use a low-side configuration.
In computer programming jargon, a heisenbug is a software bug that seems to disappear or alter its behavior when one attempts to study it.
From https://en.wikipedia.org/wiki/Heisenbug
avrdude: Expected signature for ATtiny44 is 1E 92 07
Double check chip, or use -F to override this check.
Error while burning bootloader.
avrdude: error: usbtiny_receive: Operation timed out (expected 128, got 0)
avrdude: error: usbtiny_receive: Operation timed out (expected 4, got 0)
avr_read(): error reading address 0x0000
read operation not supported for memory "flash"
avrdude: failed to read all of flash memory, rc=-2
the selected serial port avrdude: failed to read all of flash memory, rc=-2
does not exist or your board is not connected
Then it worked when I tried again.
Here you see the final gear assembly with the orthogonal channel for the locking pin and the hole filled with hot glue attached to the motor.
The motor is a Jameco 253471: DC Motor with Gearhead 12VDC 74mA (MOTOR,DC,GEAR,12V,50/1,120RPM, 1100G-CM,74MA)
The individual modules consist of a brushed DC motor from Jameco found in the Fab inventory. DC Motor with Gearhead 12VDC 74mA
The motor drives a spool for monofillament illusion thread Beadalon Supplemax 0.40mm Nylon Bead Stringing Material, 50m, Clear.
Here’s a minimal code snippet for accessing a serial device through the fab mods serialserver.js protocol. http://mods.cba.mit.edu/js/serialserver.js
mkdir serialserver
cd serialserver
wget http://mods.cba.mit.edu/js/serialserver.js
npm init
npm install ws serialport
node serialserver.js 127.0.0.1 1234
This is code meant to run on a browser, and since it accesses websocket it must be run from a local server (not file:///).
var serial = {
address: '127.0.0.1',
port: '1234',
device: '/dev/cu.usbmodem1411',
baud: 115200
}
var url = "ws://"+serial.address+':'+serial.port
var socket = new WebSocket(url)
console.log('connecting to', url)
socket.onopen = function(){
open_socket()
}
var buffer = ''
socket.onmessage = function(event){
buffer += event.data;
if(event.data == '\n'){
console.log(buffer)
buffer = ''
}
}
function open_socket(){
var msg = {}
msg.type = 'open'
msg.device = serial.device;
msg.baud = serial.baud;
msg.flow = 'none'
socket.send(JSON.stringify(msg))
console.log('opening socket', serial.device, '@', serial.baud + ' baud')
}
function send_string(str){
var msg = {}
msg.type = 'string'
msg.string = str
socket.send(JSON.stringify(msg))
}
