2-XL's new brain will be a stack of the following three boards:

• Proto Shield (for preamp circuit) w regular male headers
• Wave Shield with female stacking headers
• Metro 328 with female headers

For easier wiring, we want the Proto Shield to be on top of the stack, Wave Shield in the middle, and Metro on the bottom. To accommodate this arrangement, we'll need to assemble the boards in a specific way …

Header Swap

The Proto Shield kit includes stacking female headers which we'll solder to the Wave Shield.  We'll then take the male headers from the Wave Shield kit and solder them to the Proto Shield.

So, to assemble these two boards:

• Follow the Proto Shield's guide - but solder regular male headers pins to the PCB, and omit the 6-pin ICSP male header.

• Follow the Wave Shield guide - but solder stacking female header pins to the PCB.

Preamp circuit

The Echo's audio out signal is a bit too low for usage on the Metro's analog inputs.  To remedy this, we'll boost the signal using a simple audio amplifier circuit built on the Adafruit Proto Shield.

The amplifier uses a classic LM386 audio amplifier IC along with some resistors and capacitors.

While we're at it, we'll also include two additional resistors which will be used for connecting to 2-XL's facial LEDs:

Layout & Soldering

Using the above layout, mount all the components on the Proto Shield and solder them in place. Solder additional connections (show in green above) on the underside of the board using spare leads or solid core wire.

Next, use solid core jumper wire to make the remaining connections on the top side of the board (seen below in pink).

We'll be soldering more connections to the Proto Shield and Wave Shield later on, but first we'll tend to some software tasks …