E72 Lab


PCB Construction

In this lab you will be putting together the PCB (Printed Circuit Board) that you laid out in the first lab of the semester.  You should bring a copy of your schematic and circuit layout to lab.

Construction Techniques.

In this lab you will put together the circuit that you designed in the first lab.    You will be soldering the components to the PC board and putting everything in a case.  Later in the semester we will be adding to this circuitry.  The directions below will get you acquainted with some construction techniques.

Soldering irons, wire, PC board holders and other supplies are in Hicks 310.   The soldering irons are on timers so that they can't accidentally be left on, but you should try to remember to turn them off when you are done. The sponges should be wet so you can clean the tips of the soldering irons.  The components you need to construct your circuit are in a cabinet in Hicks 310 near the soldering stations.

If you have never soldered before, read up on circuit construction techniques, and ask me or Ed Jaoudi to demonstrate the soldering for you.

*Important:* If you are unsure about any steps in the construction (how to do it, which parts to use...) please ask me.  It is possible to correct many mistakes in PCB construction

Building your board.

The solder side of the board.

*Important:* You must do this first, before mounting any parts on the component side of the board.

The board you will be constructing is a bit unusual because is has components on both the bottom and the top of the board.  Make an appointment with Ed Jaoudi so he can show you how to attach the surface mounted components.

There are five components that must be mounted on the solder side of the board (the side without text).  There are four LED's (in PLCC-4 packages - Plastic Leadless Chip Carrier) and a LM555 oscillator (this is another relaxation oscillator) integrated circuit (in an SOIC-8 package - Small Outline Integrated Circuit).  It is critically important to get the orientation of these parts correct.  The diagram below shows the PCB layout of the board I designed (recall, green lines are on the component (or top) side, and red lines are on the solder (or bottom) side of the board) as seen from the top of the board.

If we flip the board over, we see the solder side of the board (this picture is a view from the back of the board where the surface mount items are).

 

The four LED's are mounted as shown, with the triangular notch aligned as shown (the two "Anodes" at the bottom of the PLCC package should be on the solid solder pad at the bottom of the PLCC part).   The 555 is mounted so that the line at the top of the device is aligned with the notch on the silkscreen pattern (magenta) on the device outline on the PCB.

*Important:* It is critical that you mount these parts with correct polarity.

The rest of the parts go on the component side of the board (the side with text).

The component side of the board

*Important:* Don't put any parts on the component side of the board until the surface mount components are completely installed.

The rest of the components are installed from the top of the board.  The top of the board should have writing on it.  If you are not sure, come talk to me.

On your board there are several devices that need to be installed in a specific manner.  These are described below.  Pay special attention to the ones marked "*Important*".

Testing your board

Install a 9 volt battery and then install the jumpers labeled "JPwr" and "JSlow" in my design.  If everything is working properly, the LED connected directly to the 555 should blink and the rate of blinking should change as you turn the potentiometer.

Demonstrate the board to me.


Programming the μcontroller

Important: The MSP430 (our microcontroller) is powered by 3.3V.  The breadboard power is +5V.  Be very careful attaching any signals directly from the breadboard to the microcontroller.

Programming the MSP430

  1. Make sure you have gone through the MSP430 Launchpad quickstart
  2. The schematic has 750 Ω resistors for R13, R14 and R15.  You should use 220 Ω resistors instead.
    Add 220 Ω resistors at R13, R14 and R15 to the E72 board you started building last week.  Also add a three color LED (make sure you get the polarity correct - ask if you are uncertain).
  3. Put (without soldering) 10 pin female headers with long (about 0.3" pins) into the E72 board and the connect to Launchpad (this aligns pins).  Let me know if you can't find them. *Important* It should look like the image below before soldering:

    Now solder the connectors from the top of the board.
  4. Write a program on the processor that uses both the pushbutton on the LaunchPad board and the three color LED (Connected to pins 2.2, 2.4 and 2.5) on your board.  Also make sure you connect the internal pullup resistor to the pushbutton (Port 1, Bit 3). The specific program is up to you - this just proves that everything is working.  Demonstrate for me.  Note: you don't need to plug your PCB into the wall, you can power everything through the MSP430's USB connection.

No write up this week.