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08 : Electronics Production<


Hero Shot<


Learning Outcomes<

What did I learn this week ?

  • PCB production :
    • Using the Bantam machine
  • Soldering :
    • First real soldering experience !
  • Design
    • Be carefull about RX and TX port connections !


Assignments<

This eigth week's asignments are :

  • Group :
    • Characterize the design rules for your in-house PCB production process: document the settings for your machine.
    • Document the workflow for sending a PCB to a boardhouse
    • Document your work to the group work page and reflect on your individual page what you learned
  • Individual :
    • Make and test a microcontroller development board that you designed

1. Group Assignment<

I did not have time to document it yet. For now, check Fabio's website.

2. Individual Assignment<

2.1. Design correction<

For the individual assignment, I will produce the PCB I designed during the sixth week :

However, I will first fix the few problems Axel noticed after I showed him the design :

  • The pin of the I²C port supposed to be connected to the 5V VCC is not
  • The GND pin of the left 6 pin header is not connected to the ground plane

2.2. PCB production<

For the production we used a OM10004 Bantam machine and its dedicated CAM software Bantam Tools.

After a first pass, I noticed it was not correctly engraved. We discussed with Axel and he noticed the board moved a bit when we pushed on it. Indeed, the double face tape was not uniformly installed below the board.

I then did a second pass just a bit deeper and it worked fine.

I cleaned the board to avoid short-cricuit.

And I tested the continuity with a multimeter. Everything was working and I did not detect any short-circuits.

2.3. Hardware overview<

ATTINY412<

First of all, to place the microcontroller correctly, I had to know identify the VCC pin. It is supposed to be marked by a dot like one can see on the datasheet picture below.

However I could not find it. I asked to Thomas, a electronics engineer working in our Fab Lab and he hardly found it. It is really small and just aside text which makes the task harder.

LED<

Then I had to compute the required value of the LED resistance. I looked for a LED in our electronics material and then looked for its datasheet.

In its datasheet, the max current is said to be 40mA therefore after a small computation I chose a 220 Ohm resistor.

Bypass Capacitor<

Bypass capacitor explanation

2.4. Soldering<

Microcontroller<
LED resistor<
LED and FTDI resistor<
First 6-pin header<
Remaining pin headers<
Capacitor<

2.5. Testing<

Here is the FTDI USB converter that allows me to program and communicate with the microcontroller using an USB port.

I connected it to my board :

And then Axel connected it to its computer. He uploaded a the basic blinking led program from Arduino and it worked !

We then tried to use the communication port. However, I inverted the RX and TX port. I plugged the RX pin of my microcontroller to the RX pin of the FTDI converter thinking they should be together but an RX port is a receiver and a TX port is a transmitter. Therefore, the receiver port of the microcontroller should be connected to the transmitter port of the FTDI converter.

We used then use cables to connect my board to the FTDI converter and... Oops we inverted the VCC and ground pins. The micrcontroller burnt ! I was not reactive enough to take a picture of the magic smoke :( ...