Handheld half of a two-part RF finder. Pressing the button sends a fixed-ID code that the paired bike unit answers with a beep.
Power: 12 V A27 battery. The button (SW1) is in series with the battery, so the circuit draws nothing until pressed. Code: EV1527 learning-code encoder, factory-set 20-bit ID, 330k oscillator resistor. A 0 ohm link selects button input K0; K1-K3 are left open. Transmitter: one-transistor SAW oscillator (2SC3356 with R433A 433.92 MHz SAW resonator), keyed on and off by the EV1527 data output through 47k. The PCB loop antenna (about 47 nH) is the collector load. Indicator: red LED with 4.7k, lit while transmitting.
Status: schematic only. Netlist checked against the design connection list. KiCad ERC not yet run. No PCB layout, not bench-tested. Open items: RF part values are starting values and C3 is tuned on the board; L1 is a PCB track with no footprint; battery clip footprint not assigned; check the 2SC3356 pinout and its voltage rating against a fresh 12 V battery; radio compliance not assessed.
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