<<<

abstract

This week assignement is
redraw the echo hello-world board,

• add (at least) a button and LED (with current-limiting resistor)
• check the design rules, and make it
• extra credit: simulate its operation

Circuit analysis

chip

the chip is a ATtiny44-ssu: the technical datasheet will help us to set up the circuit correctly :
In the starting circuit, 4 pins are free: PB2 and PA7 (at the left), at the right PA2 and PA3
The two ports (A and B) are bi-directional with integrated pullup resistors.
Port A contains 8bit pins
and Port B 4 bits . This caracteristics are indiferent for us because we don't use the ADC functionnality.

Led

I will use a Red Led. From the datasheet :

• continuous forward current = 30mA
• threshold voltage = 2V

So, because the circuit will be supplied in 5V, I must add a resistor :

Button

button is a switch NO (normaly open)
I checked the datasheet form pads not mistaken sense because it has 4 pins.
I connect it directly to the tiny because I plane to use the internal pullup resistor from controller.

Circuit design

As fabmodules do (almost) anything, it is possible to design PCB with the form of a descriptive language component: it is a HDL: Hardware description language.
I start from the original File hello.ftdi.44.cad and I hack it by moving a few components, and adding my own:

 
LED1=LED_1206('RLED')
pcb=LED1.add(pcb,XTAL1.x+0.05,XTAL1.y-.22,z,angle=-90)
 
pcb = wire(pcb,w,
   LED1.pad[1],
   IC1.pad[5])
 
R2 = R_1206('R2\n100');
pcb=R2.add(pcb,LED1.x-0.07,LED1.y-.15,z,angle=0)
 
pcb = wire(pcb,w,
   LED1.pad[2],
   R2.pad[2])
 
 
BUTTON1=button_6mm('BTON1')
pcb=BUTTON1.add(pcb,XTAL1.x+0.08,XTAL1.y-.55,z,angle=0)
 
 
pcb = wire(pcb,w,
   BUTTON1.pad[4],
   point(IC1.pad[6].x-0.1,IC1.pad[6].y,z))
 
pcb = wire(pcb,w,
   point(IC1.pad[6].x-0.1,IC1.pad[6].y,z),
   IC1.pad[6])
 

For the processing of the PCB, I used make_cad_png
as I found it a bit austere, I added my personal touch:

 
class flower(part):
   def __init__(self,r=.05,npetals=5):
      self.value = ''
      self.pad = [point(0,0,0)]
      self.labels = []
      d = r/2
      p = d*1.1
 
      self.shape = circle(p,0,d)
      for i in range(1,npetals):  	 
	 self.shape = add(self.shape,rotate_z(circle(p,0,d), float(360*i/npetals)))
      self.shape=subtract(self.shape,circle(0,0,d*0.9))
 

thus

 
LOGO=flower(0.05,5)
pcb=LOGO.add(pcb,x+0.14,y+0.85,z)

draw a beautyfull flower.

helloworld.cedric.cad

Simulation

I try two softwares for simulate the comportemzent of components that I added

with Qucs

Qucs it's free electronic simulation software.
I followed the e tutorial on the project site.
Qucs seems easy enough to learn, but I guess it can quickly become very complicated to simulate complex circuits.

File:HelloWorld.led.button.sch.zip
As there was no led in the library (as diodes and I could not find my settings led), I simulated one with a resistor (the time scale on which I'm studying the diagram, it makes no difference).
I then added the probes, which appear as voltmeters.
Then I placed a "transient simulation" of type linear, starting at 0 and ending at 1 ms, 2 steps to have the values ​​in the circuit in two button states: open and closed.
In the settings of the button component, I set the "time" parameter to 1ms, which is the time it takes to change state.
Finally, I placed a table and selected values ​​to display. Then I started the simulation.

conclusion
The result corresponds to what I expected: in the PA7 input, the pull-up resistor causes a voltage of 5V when the switch is open. When closed, it goes to 0V.
For the LED, this simulation confirms that the selection of a resistance of 100 ohms will cause a voltage 2V across it.

with CircuitLab

CircuitLab is an online software for electrical simulation.
It is used in a web browser, and is a bit simpler than Qucs, albeit more limited too.

I just had time to redo the schema before being asked to register ;)

Fabrication

Milling the board

I milled the circuit with the modela and fabmodules.
As with fabISP I used a spear tip.
Against by this point is worn, it is now wider than 0.4mm, so the card was ill-defined traces: below, the missed and the guilty ...

Unfortunately I have not yet received strawberries spare, so to circumvent the problem, so I set the size of the tool to 0.45mm.
This dimension is more coherent with the true size of the tip.
Fortunately it is not worn more as 0.5mm, because I saw that in fabmodules separations between tracks disappear with a tool larger than that ...
Finally, I arrived at a fairly satisfactory result:

soldering components

I'm progressing slowly in soldering SMD components.
It's not so difficult: we need only a good music ...

until we recieve 100 Ohm resistors, I put a 499 after the led: it will turn on a little less strongly.