Four-Step Octaved Sequencer

As featured in the blog post "Prototype Post-Mortem: Four-Step Octaved Sequencer", these are the prototype PCB designs for a (yet to be totally finished) fun little noise toy.

The PCB and its electronics are possibly available as a DIY electronics kit. This repo serves as the assembly guide for the kit, as well as the EAGLE project so you can fabricate your own from scratch, should you want to!

Demo video: https://vimeo.com/501110534

Assembly guide

Schematic

Annotated BOM

Part	Value	Device	Marking	Purpose
C1	10uF	Polarized, electrolytic capacitor		Tempo timer
C2	.1uF	Ceramic capacitor	104	556 IC bypass
C3	10nF	Ceramic capacitor	103	Pitch timer
C4	.1uF	Ceramic capacitor	104	4017 IC bypass
C5	.1uF	Ceramic capacitor	104	4040 IC bypass
C6	220uF	Polarized, electrolytic capacitor		Amplifier
D1		Diode		Step 1 output
D2		LED		Step 1 indicator
D3		Diode		Step 2 output
D4		LED		Step 2 indicator
D5		Diode		Step 3 output
D6		LED		Step 3 indicator
D7		Diode		Step 4 output
D8		LED		Step 4 indicator
IC1	556	556 Dual 555 timer		Timers for tempo (on left) and pitch (on right)
IC2	4017	4017 counter/divider		Decade counter for steps
IC3	4040	CD4040 or MC14040, 12-stage binary/ripple counter		Divides pitch frequency into octaves
IC4	386	LM386, low voltage audio power amplifier		Amplifier
J1	ON/OFF	Header connection		For external switch (not included)
J2	- 9V +	Header connection		9v battery snap
J3	- SPK +	Header connection		To 8ohm speaker
R1	680	Resistor	Blue Grey Brown	Max tempo
R2	220	Resistor	Red Red Brown	Tempo timer
R3	5.6k	Resistor	Green Blue Red	Pitch timer
R4	10k	Resistor	Brown Black Orange	Counter pulldown
R5	1K	Resistor	Brown Black Red	For step 1 LED
R6	1K	Resistor	Brown Black Red	For step 2 LED
R7	1K	Resistor	Brown Black Red	For step 3 LED
R8	1K	Resistor	Brown Black Red	For step 4 LED
R9	10k	Resistor	Brown Black Orange	Mixer for octave 1
R10	10k	Resistor	Brown Black Orange	Mixer for octave 2
R11	10k	Resistor	Brown Black Orange	Mixer for octave 3
R12	10k	Resistor	Brown Black Orange	Mixer for octave 4
SW1		4 position SPST DIP Switch		Octave mutes
VR1	50K	Variable resistor	503	Tempo
VR2	50K	Variable resistor	503	Step 1 pitch
VR3	50K	Variable resistor	503	Step 2 pitch
VR4	50K	Variable resistor	503	Step 3 pitch
VR5	50K	Variable resistor	503	Step 4 pitch
VR6	1K	Variable resistor	102	Volume

Notes:

• Be sure to match polarity on electrolytic caps, diodes, and LEDs! The longer leg of the LED is positive
• The four ICs don't solder directly to the PCB. Instead, solder the included sockets, then insert ICs.
• IC3 may be marked as either CD4040 or MC14040. The two models are pin-for-pin compatible.
• The J1 (on/off) header is included for convenience if you have a switch you'd like to use. If not, short the two pads together.

Hacking

All done? Try these ideas:

• Swap out for a bigger speaker to really hear the bass
• Increase gain on the 386 with a 10uF cap between pins 1 and 8
• Try bigger pots for the step tuners
• Increase R1 for reaaalllly looongggg steeeppsssssssss
• Swap R9-12 with pots to get individual volume controls for each octave as they mix together
• The 4040 has 12 "octave" outputs but we're only using four...

Known issues

This PCB was last updated April 2018. In addition to the issues from the post-mortem:

• Some footprints are slightly mis-sized and require bending leads
• Volume control is linear instead of logarithmic, so range sweep isn't great
• Battery and speaker wires need relief holes to prevent breakage over time

Version log

• 1.1.2: Adds IC, header, and polarity labels; reorders octaves
• 1.1.1: Adds mounting screw holes and a header for on/off switch (not included)
• 1.1: Initial version featured in the blog post

License

Designed by Oskitone. Please support future synth projects by purchasing from Oskitone.

Creative Commons Attribution/Share-Alike, all text above must be included in any redistribution. See license.txt for additional details.