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.
Quickly breadboarding this little gem I decided to see how portable I could make the actual build. As such I give you the…
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 surprisingly 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 rechargeable, result (courtesy of my son DJ Huck):
Details
Power
- 3.7v, 350mAh lipo battery from Adafruit.
- 9v rail using a boost switching supply based on the TI LM2735 1.6MHz DC-DC regulator.
- 3.3v rail using a linear regulator: MCP 1700.
- Microchip's MCP73833 lipo charge management controller to charge the battery from a USB Mini B connector.
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 it's hardly worth the space taken up by the extra PCB.
Audio
- TI's two-555-in-one IC the LM556 in a 14-SOIC package.
- TI LM386 Audio amplifier.
- The handsfree speaker from a dissected BlackBerry Curve (8300).
- 2 Philmore 500k linear taper potentiometers.
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 than 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:
Generated using the online SPICE engine at EveryCircuit.com
3.7 to 9v Power Supply
MPC-9v-schematic
| 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