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A blog about mobile, maker, and embedded development.


Minty Punk Console

Being the digital creature I am by day I wanted to play around with something purely analog at night. Some Googling surfaced a fun toy, the "Hello World" of analog synthesizer projects; The Atari Punk Console.

Circuit diagram of an implementation of Atari Punk Console

Quickly breadboarding this little gem I decided to see how portable I could make the actual build. As such I give you the…

The Minty Punk Console (MPC)

About the Design

I always have Adafruit permaproto boards for Altoids Smalls on hand so I decided to use this form factor. Next I sourced the knobs and pots by feel rather then by brand (I found some $2 Philmore pots at Frys that actually felt better then much more expensive parts I bought on Digikey). Given the space constraints I went with all SMT passives and ICs, sandwiching the SOIC adapters directly onto the perf board. Finally, after a fruitless search for a 3.7 to 9v DC/DC power module that could source 500mA and fit on half a minty board I was forced to go with a more complex design. Using TI’s suprisingly useful WEBBENCH Power Designer I generated an integrated design built around the LM2735 1.6MHz DC-DC regulator. With this rather expensive part ($2.80 on Digikey, actually the most expensive single part on the MPC) I was finally able to supply enough voltage and current from a 3.7v, 350mAh lipo battery to drive a speaker connected to the LM386 amplifier I had on hand.

Here’s the full portable, and rechargable, result (courtesy of my son DJ Huck):

Details

MPC in hand small.jpeg

Power

MPC callout side.png

The big lesson from this part of the build was the awesomeness of the MCP73833. It’s completely standalone (except for a couple of resistors to program the output) and the datasheet describes a circuit that should be useful for just about any portable maker project using lipo batteries. You can buy a breakout for this chip from Adafruit but the chip is so simple that its hardly worth the space taken up by the extra PCB.

Audio

MPC callout front.png

I made two improvements to the APC design when stuffing it into the mint tin. The first is to use the LM386 both to drive a speaker and to provide the proper output bias given a ground reference input and a single voltage supply. The original APC design simply used a serial capacitor on the output which makes the voltage offset frequency dependent. Using a properly biased amp means this design’s output response should be far flatter then the naive implementation.

The second feature was the breakout of the two 555 timers' output in a mini "patch bay" on the front. This adds some educational utility to the toy by allowing scopes, instered at each stage, to show how the two square waves interfere to produce the MPC’s shrill tones.

Materials

APC Values for a 3.3v Supply

For the MPC I decided to run the 555 timers using 3.3 volts. The Wikipedia design is based on a 9v supply so I had to recalculate the passives:

MPC 3.3v APC values.png
Figure 1. Generated using the online SPICE engine at EveryCircuit.com

3.7 to 9v Power Supply

MPC 9v schematic.png
Part Manufacturer Part Number Quantity Notes

Cf

Yageo America

CC0805KRX7R9BB821

1

Cin

MuRata

GRM188R60J106ME47D

1

Cout

MuRata

GRM21BR61C106KE15L

1

D1

Diodes Inc.

B220-13-F

1

VFatIo 0.5V Io 2A VRRM 20V

L1

Bourns

SRN6045-6R8Y

1

L 6.8uH DCR 0.047Ohm IDC 2.8A

Renable

Vishay-Dale

CRCW040210K0FKED

1

Resistance: 10kOhm Tolerance: 1% Power: 0.063W

Rfbb

Vishay-Dale

CRCW040210K0FKED

1

Resistance: 10kOhm Tolerance: 1% Power: 0.063W

Rfbt

Vishay-Dale

CRCW040261K9FKED

1

Resistance: 61.9kOhm Tolerance: 1% Power: 0.063W

U1

Texas Instruments

LM2735XMF/NOPB

1

"MCP", "Minty Punk Console", and all designs licenced CC 4.0 Attribution CC 4.0 Attribution