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HC-05 Pinout T-Shirt
“Your RX Wants 3.3 V.”
A nerdy electronics tee: the HC-05 ZS-040 breakout pinout, the 1k / 2k divider that turns a 5 V TX into 3.33 V for its RX, the STATE pin and the LED blinks.
from $27
Plus shipping, shown at checkout. US sales tax included where it applies.
Print: 11.3 × 13.2 in, front only.
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On the shirt
What it teaches
- The HC-05's radio is a 3.3 V part. Its RXD input is rated to 3.3 V plus 0.4 V, so a 5 V signal from a 5 V board is over the limit.
- A 1 kΩ resistor in series and a 2 kΩ resistor to ground turn 5 V into 5 × 2 / (1 + 2) = 3.33 V, comfortably inside what RXD reads as high.
- On the common ZS-040 board the pins read STATE · RXD · TXD · GND · VCC · EN, and the board itself is printed "Power: 3.6V–6V · LEVEL: 3.3V". Other breakouts use other orders, so read your silkscreen.
- STATE is low when nothing is connected and high when a device is connected (some boards don't wire it).
- A fast-blinking LED means the module is waiting for a connection; a slow blink means it is in AT command mode, at 38400 baud.
Sources
Where every fact comes from
The shirt
Fabric, fit and printing
Bella+Canvas 3001 unisex tee: combed and ring-spun cotton (heather colours are a cotton/poly blend), printed direct-to-garment and made to order. Care: wash cold, inside out; tumble dry low; don't iron the print.