Table of Contents

Lab 4

In lab_3 we built a prototype of our microphone-servo board. Now let's design the schematic of our own PCB. We'll draw an Eagle schematic of the microphone amplifier and servo supply / connector from lab 3, using the PCB design tool Eagle. It is not a very super powerful tool but installs very quickly, comes in a freeware version with limited functionality, can run on multiple platforms, and has lots of user-developed parts libraries. In lab_5 after the long Easter break, we'll complete the layout of this board.

This is an individual exercise and each student must complete it on their own laptop.

Preparation (before lab exercise)

  1. See pcb for the links to download the freeware and limited version of Eagle.
  2. Download and unpack the copper board Eagle schematic. You can use this copper schematic (PDF version here) to start to build your daughterboard, which will have a female connector to the bronze board, which has slightly different bronze board schematics as a PDF file, as shown below:

Bronze board header.


In this exercise we'll draw an Eagle schematic of the microphone amplifier and servo supply / connector from lab_3:

Microphone amplifier and servo supply

Remember that you actually modified some resistor values in lab_3 to bring the LM324 output more in the middle of it working range (see datasheet extract below).

  1. Install Eagle - see pcb.
  2. Open the Eagle dashboard by launching Eagle.
  3. Open the copper board schematic. You should see something like this view: Editing the copper board schematic.
  4. Save it off to a new schematic called mic-servo.sch.
  5. Modify your schematic so that the DIL32 header is correct for the bronze board (since we have more of these boards we will use it as the motherboard).
  6. Add or use gates (symbols) for a resistor, polarized capacitor, LM324 opamp, microphone, and 3 pin header. You have several of these already. Others you will have to either find in the libraries (and thereby learn how to search for parts), or you might have to create a gate symbol.
  7. Delete the unused symbols.
  8. Wire up the parts according to the sketch above.
  9. Ensure your designators and values are correct.
  10. Place a large label indicating the design name and designer name (your name).


When you are finished with your board schematic, send your schematic file (.sch) to schematic for Electronics for Physicists II

Eagle tips

LM324 tip

The input range of the LM234 is limited:

Input range of LM324

Data sheets