Appendix: POLY555 from Scratch


This appendix is for folks making their POLY555 from scratch without buying the kit.

under construction

More so than the other parts of the assembly guide, this part is especially a work-in-progress.




Some components may have a different designation in Kicad's BOM.

S21Slide switch1SS12D02
D21, D1, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, D14, D15, D16, D17, D18, D19, D20LED_ D5.0mm21 *LED
C62, C1, C4, C7, C10, C13, C16, C19, C22, C25, C28, C31, C34, C37, C40, C43, C46, C49, C52, C55, C58C_Disc D5.0mm_W2.5mm_P5.00mm21.1uF
BT1PinHeader 1x02_P2.54mm Vertical19v snap
C59, C56, C53, C50, C47, C44, C41, C38, C35, C32, C29, C26, C23, C20, C17, C14, C11, C8, C5, C2CP_Radial D5.0mm_P2.00mm204.7uF
U21TO-220F-3 Horizontal_TabDown1L7805
RV21, RV1, RV2, RV3, RV4, RV5, RV6, RV7, RV8, RV9, RV10, RV11, RV12, RV13, RV14, RV15, RV16, RV17, RV18, RV19, RV20Trim pot211k
R83Resistor L6.3mm_D2.5mm_P2.54mm Vertical110
R82Resistor L6.3mm_D2.5mm_P10.16mm Horizontal1100
R81, R1, R5, R9, R13, R17, R21, R25, R29, R33, R37, R41, R45, R49, R53, R57, R61, R65, R69, R73, R77Resistor L6.3mm_D2.5mm_P2.54mm Vertical21220
C64CP_Radial D8.0mm_P3.50mm1220uF
C63C_Disc D5.0mm_W2.5mm_P5.00mm147nF
C61C_Disc D5.0mm_W2.5mm_P5.00mm1.22uF
C60, C3, C6, C9, C12, C15, C18, C21, C24, C27, C30, C33, C36, C39, C42, C45, C48, C51, C54, C57C_Disc D5.0mm_W2.5mm_P5.00mm2010nF
R79, R75, R71, R67, R63, R59, R55, R51, R47, R43, R39, R35, R31, R27, R23, R19, R15, R11, R7, R3Resistor L6.3mm_D2.5mm_P2.54mm Vertical20100
U1, U2, U3, U4, U5, U6, U7, U8, U9, U10, U11, U12, U13, U14, U15, U16, U17, U18, U19, U20DIP-8_W7.62mm20555
S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, S11, S12, S13, S14, S15, S16, S17, S18, S19, S20SW_TH_Tactile_Omron_B3F-10xx206x6x6 tactile
R2, R6, R10, R14, R18, R22, R26, R30, R34, R38, R42, R46, R50, R54, R58, R62, R66, R70, R74, R78Resistor L6.3mm_D2.5mm_P2.54mm Vertical20100k
R4, R8, R12, R16, R20, R24, R28, R32, R36, R40, R44, R48, R52, R56, R60, R64, R68, R72, R76, R80Resistor L6.3mm_D2.5mm_P2.54mm Vertical2010k

* 21 LEDs total in 3 colors: 1 for on/off indicator, 12 for natural notes, 8 for accidental


SocketDIP-821For 555s and 386
Plexiglass136mm x 92mm x 2.5mm12mm and 3mm also work
1" screw4-40 1" long4
1/4" screw4-40 1/4" long2
Square nut4-406


Almost all components on the POLY555 are jelly bean parts, except...



  • Low voltage options are better for battery performance.
  • Voltage regulator's output should fall within supply voltage. This likely won't be a problem.
  • Frequency range needs to cover the full spectrum of notes.


ModelObserved frequency range *
TLC555CP **147.1 - 769.2
LMC555CN **147.1 - 877.2
LM555CN73.42 - 862.1

* With default component values from schematics.

** Kits ship with one of these.

If using a different 555, breadboard the timer circuit first to determine its range, adjusting the other components if necessary to get to the desired note range. The downside to a wider frequency range is that it's harder to tune!

Tactile switches#

These are common enough. Make sure actuator height is 6mm, otherwise you'll be editing BUTTON_HEIGHT.


The speaker is a SC700208, measuring 71mm x 41mm x 25mm. Its shape is some kind of standard; there are others that are nearly identical, like the S15X25VA.

Crucially, the depth of the cone and magnet diameter fit perfectly into the enclosure. The mounting screw holes are currently unused, though I may change that in future versions.

Using a speaker with different dimensions will necessitate modifying the enclosure to fit.


IDK what the model is called but they look like this and are readily available in bulk on eBay:

Example trimpots

It is not the Bourns 3306 series.

Since it's used for both the tuners and the volume control, you may need to modify the volume wheel to fit if using a different pot.