Ingestible event marker systems

An ingestible event marker comprising:

• a battery section including two electrodes configured to supply a battery voltage upon contacting a body fluid by generating a current between the two electrodes using the body fluid as a conductive medium;
• an integrated circuit (IC) coupled to the battery section and configured to store an identification code;
• and
• wherein the IC comprises:
• a transmission switch transistor coupled to the two electrodes;
• a control logic configured to control the transmission switch transistor to control an impedance between the two electrodes to alter the current flowing through the body fluid to transmit a coded signal representing the identification code using binary phase-shift keying (BPSK) modulation via a carrier frequency generated by an oscillator;
• a power supply circuit coupled to the control logic;
• and
• a capacitor coupled to the control logic and the power supply circuit, the capacitor configured to be chargeable by the battery voltage.