MEAP 4b hardware description


MEAP's circuit board was designed using the fantastic open source softwareKicad. If you really want to know what is going on in the hardware world of MEAP, the best way is to open the design files (which are located within the hardware design folderon the MEAP Github) in Kicad, however this page will provide a surface level summary.


important chips used:


Schematic





PCB Pads





Hackable bits


Auxiliary multiplexer

MEAP includes an extra 8-input multiplexer that is by default not hooked up to anything. Any extra analog or digital inputs such as switches or potentiometers can be soldered to it. Use the meap.readAuxMuxDigital() or meap.readAuxMuxAnalog() reads all channels of this multiplexer as digital or analog values respectively and store the results in the meap.aux_mux_vals array. The 2x4 grid of inputs in the top right of your board correspond to the indices of the array as shown below (ie. if you want to retrieve the value of the input soldered into the top left inlet it will be located at meap.aux_mux_vals[4])
._ ._
|0|/1\
|_|\_/
._ ._
/3\/2\
\_/\_/
._ ._
/6\/4\
\_/\_/
._ ._
/5\/7\
\_/\_/

Secret bonus multiplexer pads

The back side of the MEAP board contains pads for an extra multiplexer (74LV4051D in SOIC16 3.9mmx9.9mm package). It is connected to the same address pins as all other multiplexers on the board. If it is used, it is recommended to add strain relief(eg. hot glue) to any wires soldered to the surface mount pads.


Unused GPIO Pins

Several unused GPIO pins are broken out for analog/digital input or output.


Repurposing used GPIO Pins

If you need more pins for your project, some of the pins used by MEAP can be repurposed without too much trouble.


I2C Pins

GPIO pins 21 (SDA) and 14 (SCL) are configured as an I2C port which is used to configure the audio codec. Other I2C devices can be added to the same data and clock lines. You could mayyyybe use these pins for other purposes so long as they are still able to send messages to the audio codec on boot.


Adding additional multiplexers

The multiplexer address pins A, B and C are broken out on the board. These can be connected to any other 8-channel multiplexers wired on auxilliary circuit boards for additional inputs.


External power

If you have an external 5v power supply you want to use to power your MEAP, you can solder it directly into the V_IN pin. The back of the board contains pads to solder on a power regulator for any external power source over 5v. A TLV1117-50 along with two 22uF 1210 ceramic capacitors can be soldered on to use this. The external power source that needs to be regulated can be soldered onto HI_IN and GND. Input voltage can technically be up to 16V but I wouldn't recommend going above 9. I have not had great success with getting smooth power out of this regulator so I've been happy sticking to USB power for now!


SGTL5000 Bonus I/O

The audio codec chip used has two separate outputs whose volume can be controlled independently.

The audio codec chip also has two inputs, but only one can be active at a time.