add pinouts and schematic

2026-09-11 18:50:26 -07:00
parent 8629ba2d22
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+# Baby toy → DFPlayer audio trigger
+
+Interfacing a battery-powered toy's button and LED matrix (4.8V, 3×AAA,
+active-high buttons / active-low LEDs) with a DFPlayer Mini (active-low,
+3.3V-pulled trigger pins) and a Seeed XIAO nRF52840.
+
+## Schematic
+
+![Wiring diagram: toy buttons through a darlington array to the DFPlayer, and toy LEDs through diodes to the XIAO](schematic.svg)
+
+## Bill of materials
+
+| Part | Notes |
+|---|---|
+| Toy button/LED PCB | Existing hardware. 4.8V from 3×AAA. Buttons short to +4.8V, LEDs short to GND. |
+| DFPlayer Mini | Trigger pins are active-low, internally pulled high. |
+| Seeed XIAO nRF52840 | 3.3V logic. Reads LED sense lines; optional UART link to DFPlayer for extra tracks. |
+| ULN2003A (7ch) or ULN2803A (8ch) | Through-hole DIP darlington array. Pick based on how many button lines you need; spare channels can also drive LEDs if a GPIO can't sink enough current. |
+| 100 kΩ resistors (optional) | One per button line, only if that pin floats when unpressed. |
+
+## Button → DFPlayer path (via darlington array)
+
+Each toy button input goes straight into a ULN200x input pin — no external
+resistor needed, it's built in (~2.7 kΩ, rated well above 4.8V). The
+corresponding output pin goes straight to a DFPlayer trigger pin.
+
+| Toy button | ULN200x input (pin) | ULN200x output (pin) | DFPlayer trigger pin |
+|---|---|---|---|
+| Button 1 | IN1 (1) | OUT1 (16) | IO1 / K1 |
+| Button 2 | IN2 (2) | OUT2 (15) | IO2 / K2 |
+| Button 3 | IN3 (3) | OUT3 (14) | K3 |
+| Button 4 | IN4 (4) | OUT4 (13) | K4 |
+| ... | ... | ... | ... |
+
+Input and output pins are mirrored (IN1 pairs with OUT1, not OUT7) — check
+your chip's datasheet pinout before wiring, it's easy to get backwards.
+
+Pin 8 is chip GND. Pin 9 (COM) isn't needed for this application — it's
+only relevant when driving inductive loads like relays or motors.
+
+## LED drive path (XIAO → toy LEDs)
+
+The XIAO drives the LEDs directly (random/sequential blink pattern) — it
+doesn't sense them. The toy originally lit each LED by grounding its pin,
+so the XIAO just needs to sink that same pin to reproduce that behavior.
+
+| XIAO GPIO | Driver | Toy LED pin |
+|---|---|---|
+| GPIOx | direct pin, or spare ULN200x channel | LED 1 |
+| GPIOx | direct pin, or spare ULN200x channel | LED 2 |
+| GPIOx | direct pin, or spare ULN200x channel | LED 3 |
+
+If the toy board already has a current-limiting resistor in series with
+each LED (likely, since the pin was safely grounded directly before), a
+bare GPIO configured as output and driven low may be enough — check the
+LED's current draw against the nRF52840 pin's sink rating first. If it's
+too high, route that line through an unused channel on the same
+ULN2003A/2803A used for the buttons instead, same wiring pattern, just
+with the XIAO as the input source.
+
+To turn an LED off, leave the pin undriven (input / Hi-Z) rather than
+driving it HIGH — at 3.3V vs. the toy's 4.8V rail, a driven-high pin may
+not fully extinguish the LED depending on its forward voltage.
+
+## Common ground
+
+Toy battery GND, ULN200x GND (pin 8), DFPlayer GND, and XIAO GND must all
+be tied together. Without a shared ground reference, none of the switching
+above works.
+
+## Notes
+
+- **Floating button lines**: if a button pin doesn't idle at a defined
+  level when unpressed, add a 100 kΩ pull-down per line to prevent
+  spurious triggers.
+- **Optional UART link**: the XIAO can also drive the DFPlayer directly
+  over UART for tracks beyond what the hardware trigger pins support,
+  independent of the darlington-array trigger path above.