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Teacher's Guide

This page holds the Purchasing Guide section of the Teacher's Guide for Open Study Buddy.

Purchasing Guide

The Study Buddy's 2.1-inch round GC9B72 display showing a clock and a two-day weather forecast, held on an acrylic stand

The whole book runs on one kit, the Study Buddy base kit: a Raspberry Pi Pico 2 WH, a 2.1-inch 360×360 round color display (GC9B72), an INMP441 I²S microphone, a MAX98357A I²S amplifier with a small speaker, three push buttons, a breadboard and wiring. One kit costs about $28 at single-unit prices and about $21 per student for a class of 20. Every part except the Pico ships from China in 8–12 days (median 9) in our 2026 AliExpress orders, so order at least three weeks before the hardware chapters start, and four to five weeks ahead for a full classroom set.

Prices checked October 2026

Component prices move, and marketplace listings turn over constantly. Treat every figure here as a planning estimate, not a quote. Each part shows the low and high AliExpress prices we found in web searches on October 20, 2026, with eBay and Amazon prices for comparison. Figures marked estimate could not be confirmed from a current listing, and each one says why.

Don't order the wrong one: a 360×360 SPI display with the GC9B72 controller

The kit's driver (lib/gc9b72.py) only works with the 2.1-inch, 360×360, 4-wire SPI round display built on the GC9B72 controller. Marketplaces list 2.1-inch round 480×480 panels (ST7701, RGB or MIPI interface) and 1.28-inch GC9A01 round displays right beside it, with nearly identical photos. Neither will work. Look for "GC9B72" and "360x360" in the listing title.

Summary of Parts List

Required

Optional

None. Every part above is used by the kit's tests, and the base kit has no battery, enclosure or SD card yet.

Price ranges and lead times at a glance:

Part Qty Price range AliExpress lead time
Raspberry Pi Pico 2 WH 1 AliExpress $3.53–$31.09 (genuine "original" boards $20.75); eBay ~$15–$23; Amazon $13.99 (no headers)–$18.95 (WH); Micro Center $6.99 Not recommended from AliExpress. Micro Center: same-day pickup, or ships in 5–7 business days
2.1-inch round display (GC9B72) 1 AliExpress $5.39–$6.12; eBay ~$8–$15 (estimate); Amazon: no matching listing found 8–12 days (median 9). Glass panel, so allow for a breakage spare
INMP441 microphone 1 AliExpress $0.99–$4.39; eBay ~$3–$8; Amazon $8.54–$9.99 per 3-pack ($2.85–$3.33 each) 8–12 days (median 9)
MAX98357A amplifier 1 AliExpress $0.93–$1.53; eBay ~$2–$6 (estimate); Amazon $6.88 per 2-pack to $11.99 per 6-pack ($2.00–$3.44 each) 8–12 days (median 9)
Speaker, 3525 8 Ω 2 W 1 AliExpress $0.58–$2.80; eBay $1.47 + $3.50 shipping; Amazon $12.99 per 10-pack ($1.30 each) 8–12 days (median 9). Small sealed speaker, no magnet or battery shipping rules
6×6 mm push buttons 3 AliExpress ~$0.01–$0.03 each in 100-packs (estimate); eBay ~$3–$6 per 100 (estimate); Amazon $4.99 per 100 8–12 days (median 9)
830-point breadboard 1 AliExpress $0.68–$2.61; eBay ~$2–$7 (estimate); Amazon $19.99 per 10-pack ($2.00 each) 8–12 days (median 9). Bulky for its weight: ten boards ship as a larger parcel
Male-to-male jumper set 1 set AliExpress/eBay/Amazon 65-piece sets $1.99–$5.50 8–12 days (median 9)
Dupont ribbon, 40-wire M-F 20 cm 8 wires AliExpress from ~$0.99; eBay ~$2–$4 (estimate); PiShop US $2.95 8–12 days (median 9)
Micro-USB data cable 1 AliExpress ~$0.80–$2.00 (estimate); eBay ~$2–$4 (estimate); Amazon $7.49–$9.44 per 3-pack ($2.50–$3.15 each) 8–12 days (median 9), or buy on Amazon

Estimated total per kit:

Kit One kit Per student, class of 20
Study Buddy base kit ~$28.33 ~$21.12

The one-kit figure uses each part's single-unit price. If you are building just one kit, the real out-of-pocket cost is higher (about $40) because buttons, cables and breadboards come in packs. The class figure rounds each order up to the pack, and the Pico 2 WH stays at its fixed $6.99 retail price at any quantity.

Raspberry Pi Pico 2 WH

Raspberry Pi Pico W, which looks nearly identical to the Pico 2 W

Shown: the original Pico W, which looks nearly identical to the Pico 2 W. Photo by SparkFun Electronics, CC BY 2.0.

Used in: Study Buddy base kit (×1)

Used for: Chapter 4: The Pico Kit Hardware and Wiring and every chapter after it, including Wi-Fi in Chapter 13: Wi-Fi, HTTP, and Connecting to the Agent. It runs the student's MicroPython and talks to every other part.

The Pico 2 W is Raspberry Pi's RP2350 microcontroller board with 2.4 GHz Wi-Fi and Bluetooth. Buy the WH version, which has its header pins already soldered so it drops straight into the breadboard. The plain "Pico 2 W" has bare pads.

Requirements: It must be a Pico 2 W (RP2350). The older Pico W (RP2040) and the plain Pico 2 (no Wi-Fi) look almost the same in listing photos. The book's audio, FFT and Wi-Fi chapters assume the RP2350's 520 KB of RAM and the wireless chip. The radio is 2.4 GHz only, so confirm with your school's IT team that a 2.4 GHz network is available.

Prep work: None for the WH. A plain Pico 2 W needs its headers soldered on (about 15 minutes).

Cost: ~$6.99 each in quantity 1 (Micro Center "Pico 2W with Header", SC1634) · ~$6.99 each in a classroom order of 20+ · ~$6.99 at district scale (estimate: we assume the fixed retail price holds). Price range: AliExpress $3.53–$31.09 (the low end is a promotional listing of uncertain origin; listings titled "100% New Original" were $20.75); eBay about US$15–$23 (eBay Australia listings at AU$23.75–AU$34.98; we could not load US eBay results); Amazon $13.99 for the Pico 2 W without headers and $18.95 for a pre-soldered version.

AliExpress lead time: Not recommended. Marketplace Picos cost two to four times the Micro Center price and are the boards most likely to be relabeled. Micro Center stores have it the same day, and its online store lists "usually ships in 5–7 business days".

Trusted sellers: Micro Center, Adafruit, SparkFun, Digi-Key and PiShop.us. Genuine boards say "Pico 2 W" on the silkscreen and carry an RP2350 chip.

Search keywords: Raspberry Pi Pico 2 WH, Pico 2 W with header, SC1634

Where to buy:

2.1-inch Round Display (GC9B72, 360x360)

The 2.1-inch round GC9B72 display showing a large clock and weather icons, with its 10-pin header at the bottom

Used in: Study Buddy base kit (×1)

Used for: Chapter 5: Display Basics: Pixels, Color, and Frame Size and Chapter 6: Drawing Directly to Display Regions, then the face, text and level meter in every later chapter.

A 2.1-inch round IPS color screen with 360×360 pixels and a GC9B72 controller, driven over 4-wire SPI at 3.3 V. The module has a 10-pin header (GND, VCC, SCL, SDA, RST, DC, CS, BL, SDO, TE). The kit uses the first eight. GalaxyCore has never published a GC9B72 datasheet, so the book's driver was ported from the one known-good public init sequence. That makes the exact controller matter more than usual.

Requirements: It must say GC9B72, 360x360 and SPI. The 480×480 2.1-inch round panels need an RGB or MIPI interface that the Pico does not have.

Prep work: None. The header comes soldered. Peel off an 8-wire strip of the ribbon cable for it (see below).

Cost: ~$6.12 in quantity 1 (the AliExpress listing we bought from, US$6.12) · ~$5.39 each in a classroom order of 20+ (the lowest current AliExpress search price) · no district tier found. Price range: AliExpress $5.39–$6.12 (TZT's own store lists it at $3.45); eBay ~$8–$15 (estimate: we could not load current US eBay results); Amazon: no matching 360×360 GC9B72 listing found, only the 480×480 panels that will not work. A European marketplace lists it at €14.64 plus shipping.

AliExpress lead time: 8–12 days (median 9), the same as our other AliExpress packages. The glass panel ships in a bigger padded box, and a cracked screen means reordering and another 9 days, so buy one or two spares.

Spotting a bad batch: A blank screen with the backlight on usually means a wiring mistake, so run test 04 first. A panel with a dead line or a dark sector after a correct test is a defect. Set it aside and use a spare.

Search keywords: GC9B72 2.1 inch round display 360x360, 2.1 inch round TFT SPI GC9B72

Where to buy:

INMP441 I2S Microphone

INMP441 microphone breakout board, round, with a loose six-pin yellow header beside it

Used in: Study Buddy base kit (×1)

Used for: Chapter 8: I2S Audio: Recording and Playing Sound, Chapter 11: Microphone Calibration and Push-to-Talk and Chapter 12: Wake-Word Detection. It turns the student's voice into 24-bit samples.

A digital MEMS microphone with its own ADC, sending samples straight to the Pico over I²S. Buy the INMP441 by name. The "INMP441-compatible" MS3625 and MS4030 boards are cheaper, but the kit's calibration numbers were measured on the INMP441. It is a 3.3 V part: VDD goes to 3V3, never to VBUS.

Prep work: Some minor soldering required. Most listings ship with the six-pin header loose, as in the photo, and soldering it takes about 5 minutes per board. Listings sold as "solderless" have the header fitted and are worth the extra few cents for a no-solder kit. Tie the L/R pin to GND.

Cost: ~$3.00 in quantity 1 (AliExpress singles at $2.19–$4.39) · ~$1.00 each in a classroom order of 20+ (AliExpress listings around $0.99) · ~$0.89 each at district scale (an Alibaba tiered listing at $0.89 for 10–999 pieces). Price range: AliExpress $0.99–$4.39 (coin-deal listings as low as $0.33 are for new shoppers only); eBay ~$3–$8 (UK listings at £5.82–£5.99, Germany €2.28 plus €1.60 shipping); Amazon $8.54–$9.99 per 3-pack.

AliExpress lead time: 8–12 days (median 9).

Spotting a bad batch: A dead or badly soldered microphone reads as all zeros, which looks exactly like the swapped-wire fault in the kit README. Check the wiring, then the solder joints, then swap in a spare.

Search keywords: INMP441 I2S microphone module, INMP441 MEMS omnidirectional, INMP441 solderless

Where to buy:

MAX98357A I2S Amplifier

MAX98357A I2S amplifier breakout, top side MAX98357A I2S amplifier breakout, bottom side

Used in: Study Buddy base kit (×1)

Used for: Chapter 7: Buttons, State Machines, and Device Modes (the volume beep) and Chapter 8: I2S Audio: Recording and Playing Sound, then every chapter where the buddy speaks. It turns I²S audio from the Pico into power for the speaker.

A digital-to-analog converter and a 3 W class-D amplifier on one small board, with seven pins (LRC, BCLK, DIN, GAIN, SD, GND, VIN) and a two-screw output terminal. The kit drives its GAIN pin from GP18 so software can pick 6, 9 or 12 dB. Buy the mono MAX98357A breakout, not the analog PAM8403 boards or the larger stereo TDM boards that show up in the same searches.

Prep work: Some minor soldering required on most listings. The seven-pin header and the screw terminal usually ship loose, which takes about 10 minutes per board. Some listings are sold as "pre-soldered" for about the same price, and we recommend those for a no-solder kit.

Cost: ~$1.53 in quantity 1 · ~$0.99 each in a classroom order of 20+ (most AliExpress listings) · no district tier found. Price range: AliExpress $0.93–$1.53 (pre-soldered listings about $0.99); eBay ~$2–$6 (estimate: we could not load current US eBay results; Adafruit's genuine breakout is $5.95); Amazon $6.88 for a 2-pack, $7.59 for 3, $8.54 for 4 and $11.99 for 6 ($2.00–$3.44 each).

AliExpress lead time: 8–12 days (median 9).

Spotting a bad batch: No sound with test 05 is almost always the I²S pin rule (LRC must be the pin right after BCLK) or a loose screw terminal. If test 02 reports no warnings and the speaker is known good, swap the board.

Search keywords: MAX98357A I2S amplifier module, MAX98357 I2S 3W class D pre-soldered

Where to buy:

Speaker (3525, 8 ohm, 2 W)

Photo pending. See the image brief.

Used in: Study Buddy base kit (×1)

Used for: Chapter 8: I2S Audio: Recording and Playing Sound and every chapter where the buddy beeps, plays back a recording or speaks.

A small sealed "3525" cavity speaker, 35 × 25 mm, with a red and black lead ending in a 2-pin JST PH 2.0 plug. The kit's speaker is the 8 Ω, 2 W version: it was measured at 7.4 Ω DC resistance. The same listings also sell a 4 Ω, 3 W version. Either works with the MAX98357A, but the 8 Ω one is quieter and draws less current from the Pico's USB supply, so stay with it.

Prep work: About 2 minutes. Cut off the JST plug, strip 5 mm from each wire, and clamp the wires in the amplifier's screw terminal (red to +).

Cost: ~$1.09 in quantity 1 · ~$0.58 each in a classroom order of 20+ (the lowest current AliExpress search price) · no district tier found for this exact speaker. Price range: AliExpress $0.58–$2.80 (the $2.80 listing is the one the prototype kit came from); eBay $1.47 plus $3.50 shipping (a UK listing); Amazon $12.99 for a 10-pack ($1.30 each).

AliExpress lead time: 8–12 days (median 9). The speaker is small and has no battery, so it ships like any other small packet.

Search keywords: 3525 speaker 8 ohm 2W, 3525 cavity speaker JST PH2.0

Where to buy:

Momentary Push Buttons (6x6 mm)

Momentary tactile push button with a round cap and four leads

Used in: Study Buddy base kit (×3: Mode, Up and Down)

Used for: Chapter 7: Buttons, State Machines, and Device Modes and push-to-talk in Chapter 11.

Standard 6×6 mm, four-leg, through-hole tactile switches. Each one connects GP13, GP14 or GP15 to GND and uses the Pico's internal pull-up, so no resistor is needed. Colored caps are optional but help students tell Mode from Up and Down.

Prep work: None. They are breadboard-ready as shipped. Show students that the four legs are two connected pairs, so a button wired with both wires on the same side reads "pressed" all the time.

Cost: ~$0.15 for three in quantity 1 (a 100-pack is $4.99 on Amazon) · ~$0.05 each in a classroom order of 20+ (one 100-pack covers 20 kits with 40 spares) · ~$0.04 each at district scale (Alibaba switches at a 1,000-piece minimum order). Price range: AliExpress ~$0.01–$0.03 each in 100-packs (estimate: not re-checked this month); eBay ~$3–$6 per 100 (estimate); Amazon $4.99 per 100.

AliExpress lead time: 8–12 days (median 9).

Spotting a bad batch: Legs bent too short to seat, or switches that never click. Discard the odd bad one; the 100-pack has plenty of spares.

Search keywords: 6x6mm tactile push button 4 pin, tact switch 6x6x5 DIP

Where to buy:

Solderless Breadboard (830 Point)

Full-size 830-point solderless breadboard, transparent, with power rails along both edges

Photo: oomlout, CC BY-SA 2.0 via Wikimedia Commons

Used in: Study Buddy base kit (×1)

Used for: Chapter 4: The Pico Kit Hardware and Wiring and every wired test after it.

A full-size 830 tie-point breadboard ("MB-102"). Buy the full size: the Pico, microphone, amplifier and three buttons do not fit on a 400-point half-size board, and the chapter's advice to keep the microphone's wires away from the amplifier's needs the room.

Prep work: None. Optionally mark the 3V3 and GND rails with a permanent marker; the microphone is damaged by 5 V.

Cost: ~$2.00 in quantity 1 (an Amazon 10-pack at $19.99) · ~$1.10 each in a classroom order of 20+ · ~$0.40 each at district scale (Alibaba listings at $0.40 for 5–49 pieces, plus a flat shipping charge). Price range: AliExpress $0.68–$2.61 (most around $0.99–$1.21); eBay ~$2–$7 (estimate; a single board is $6.94 from Circuit Specialists); Amazon $19.99 per 10-pack.

AliExpress lead time: 8–12 days (median 9). Breadboards are light but bulky, so a 20-board order arrives as a larger parcel. Some sellers split it into several packages that arrive on different days.

Spotting a bad batch: A rail or row clip that is not bent properly, so wires will not seat. Test each board with a jumper on arrival and throw out the odd bad one.

Search keywords: 830 point solderless breadboard, MB-102 breadboard

Where to buy:

Male-to-Male Jumper Wires

A bundle of male-to-male breadboard jumper wires in assorted colors

Used in: Study Buddy base kit (×1 set)

Used for: Chapter 4: power and ground rails, the buttons, and the microphone and amplifier wiring on the breadboard.

A mixed-length set of male-to-male jumpers. The kit needs about 20 wires, so a 65-piece set leaves spares.

Prep work: None.

Cost: ~$2.00 per set in quantity 1 · ~$2.00 per set in a classroom order of 20+ · ~$1.00 per set at district scale (estimate: no current bulk listing found). Price range: 65-piece sets at $1.99–$5.50 across AliExpress, eBay and Amazon (October 2026 checks for our FFT kit; not re-checked per site).

AliExpress lead time: 8–12 days (median 9).

Spotting a bad batch: Pin ends that wobble in their crimp cause intermittent faults that look like code bugs. Throw out any jumper whose tip moves.

Search keywords: breadboard jumper wires male to male, 65 pcs jumper wire kit

Where to buy:

Dupont Ribbon Cable (Male-to-Female, 20 cm)

A multicolored Dupont ribbon cable with male pins on one end and female sockets on the other

Used in: Study Buddy base kit (×8 wires, one-fifth of a 40-wire ribbon)

Used for: The display cable in Chapter 5: Display Basics: Pixels, Color, and Frame Size.

A 40-wire ribbon of Dupont jumpers with a female socket on one end and a male pin on the other. Peel off an 8-wire strip for the display: the female ends push onto the display's header and the male ends go into the breadboard. config.py records a color for each display wire (SCL orange, SDA yellow, RST green, DC blue, CS purple, BL gray, VCC red), so peel the strip where those colors line up. One ribbon makes cables for five kits.

Prep work: Peel the ribbon into 8-wire strips, about 1 minute per kit. Keep the strip intact: it stays in pin order and is far harder to miswire than loose jumpers.

Cost: ~$2.95 per ribbon in quantity 1 (PiShop US) · ~$1.00 per ribbon in a classroom order of 20+ (AliExpress from about $0.99), about $0.20 per kit · ~$0.65 per ribbon at district scale (an Alibaba listing). Price range: AliExpress from ~$0.99; eBay ~$2–$4 (estimate); PiShop $2.95.

AliExpress lead time: 8–12 days (median 9).

Spotting a bad batch: Female sockets too loose to grip a header pin. Test-fit one strip on the display when the order arrives.

Search keywords: dupont jumper wire 40 pin male to female 20cm, M-F dupont ribbon cable

Where to buy:

Micro-USB Data Cable

USB-A to Micro-USB cable, showing both plugs

Photo: Electronicgrup, CC BY-SA 3.0 via Wikimedia Commons

Used in: Study Buddy base kit (×1)

Used for: Chapter 4 and every chapter after it. It powers the kit and carries the Thonny connection.

The Pico 2 WH has a Micro-USB port, not USB-C. The cable must carry data: charge-only cables look identical and are the most common reason a Pico "isn't detected" on day one. If your laptops have only USB-C ports, buy USB-C to Micro-USB cables. A computer USB port supplies about 500 mA, which is enough for this kit at the volumes the tests use.

Confirm it says data or sync

Look for "data", "sync" or "480 Mbps" in the listing. A cable sold only as a "charging cord" may have no data wires at all.

Prep work: None. Test each cable with a Pico in Thonny on arrival and discard any that only charge.

Cost: ~$2.50 in quantity 1 (Cable Matters 3-pack, $7.49 on Amazon) · ~$2.50 each in a classroom order of 20+ (seven 3-packs) · ~$1.00 each at district scale (estimate). Price range: AliExpress ~$0.80–$2.00 (estimate: not checked this month); eBay ~$2–$4 (estimate); Amazon $7.49–$9.44 per 3-pack.

AliExpress lead time: 8–12 days (median 9). Cables are the easiest part to buy domestically the week of the lab if a few are missing.

Search keywords: micro USB data sync cable 3ft, USB-C to Micro-USB data cable

Where to buy:

Purchasing Strategy

Ordering lead time

These figures are based on our 2026 AliExpress orders to Minnesota: 8 packages, measured from order date to delivery.

Source Orders measured Typical delivery Notes
AliExpress 8 packages 8–12 days (median 9) Every 2026 package arrived within two weeks
Micro Center — same day in store; online "ships in 5–7 business days" The place to buy the Pico 2 WH
Amazon — 1–3 days with Prime (estimate, not measured) The fallback for cables, buttons and breadboards

The per-part notes above flag the parts that ship differently: the display (fragile glass in a larger padded box) and the breadboards (bulky, sometimes split into several packages). The kit has no batteries, so no part is held up by lithium shipping rules. If a later version adds a battery pack, expect it to ship separately and take longer.

Our recommendation: place AliExpress orders at least three weeks before you need the parts, and four to five weeks ahead for a full classroom set. Eight packages is a small sample, and the extra weeks mean a lost package or a cracked display can be reordered and still arrive in time. Use Micro Center or Amazon for last-minute gaps. Expect longer delays around Lunar New Year, when Chinese factories and shipping largely stop for two weeks or more.

Buy one, then buy twenty. Order a single display, microphone and amplifier from a seller first, confirm they are the GC9B72 360×360 display, a genuine INMP441 and a mono MAX98357A, then place the classroom order with the same sellers.

Order spares. Add 10–15% over the class count for the display, microphone, amplifier and Pico. Two spares of each add about $30 to a class order.

Watch the pack sizes. Buttons come in hundreds, breadboards in tens and cables in threes. Round the order up to the pack, not to the roster.

Buy boards from authorized resellers. Micro Center sells the genuine Pico 2 WH for less than any marketplace listing we found.

Expect the odd bad unit, not a bad order. Test every part on arrival with the kit's numbered tests (01–07) and discard the occasional dud.

Check your district's purchasing rules first. Many districts cannot reimburse AliExpress orders and require a domestic vendor with a W-9. If so, the Amazon and Micro Center prices are your real prices. The round display has no Amazon listing we could find, so a district with that rule will need an exception for it or a different domestic seller.

Classroom Order Worksheet

Part Required? Used in kits Qty per student Qty for 20 students Est. cost for 20
Raspberry Pi Pico 2 WH Required Study Buddy base 1 20 $139.80
2.1-inch round display (GC9B72) Required Study Buddy base 1 20 $107.80
INMP441 microphone Required Study Buddy base 1 20 $20.00
MAX98357A amplifier Required Study Buddy base 1 20 $19.80
Speaker, 3525 8 Ω 2 W Required Study Buddy base 1 20 $11.60
6×6 mm push buttons Required Study Buddy base 3 100 (1 pack of 100) $4.99
830-point breadboard Required Study Buddy base 1 20 $22.00
Male-to-male jumper set Required Study Buddy base 1 set 20 sets $40.00
Dupont ribbon, 40-wire M-F 20 cm Required Study Buddy base 1/5 ribbon 4 ribbons $4.00
Micro-USB data cable Required Study Buddy base 1 21 (7 three-packs) $52.43
Total $422.42

Per student: ~$21.12. Add about $30 for two spares each of the Pico, display, microphone and amplifier.

Shared classroom tools

These are bought once and reused for years, so they are kept out of the per-student figure.

Tool Cost How many
Soldering iron and solder (for microphone and amplifier headers, unless you buy pre-soldered boards) $15–40 1 per 4–6 students
Wire strippers (for the speaker leads) $8–15 1 per table
Small flat screwdriver (for the amplifier's screw terminal) $2–5 1 per table