The RoboRoach operates using PWM (Pulse Width Modulation) with controlled amplitude via a digital potentiometer. Instead of directly regulating stimulation current, the system delivers a biphasic PWM signal to the cockroach’s antennae. This allows voltage to be alternately injected and removed, which avoids DC biasing and prevents harm to the cockroach.
Variable Stimulation Voltage
The stimulation voltage is not fixed; rather, it varies based on the frequency of the stimulation pulses and the overall signal amplitude, both of which are influenced by several variable factors.
Current Pathway
The electrical current follows this path:
- A 3V DC battery supplies power.
- Power reaches the microcontroller, which outputs stimulation pulses via a GPIO pin (at battery voltage), controlled through a smartphone app.
- The signal passes through a digitally controlled variable resistor (digital potentiometer), which sets the pulse amplitude.
- It continues through a series capacitor, which:
- Shapes the current waveform
- Prevents DC biasing
- Improves biological safety by reducing electrolysis and tissue damage
- The current flows through a silver wire electrode, connected to the cockroach’s antenna. Impedance here varies with insertion depth, contact quality, and tissue interface.
- The signal travels through the cockroach’s body, which has biological and variable impedance based on the individual specimen.
- The return path completes through the ground back to the battery, which includes some equivalent series resistance (ESR).
Impedance Variability
Because of variable and uncontrolled impedance, particularly from biological tissue and electrode contact, the exact current the exact current through the antenna cannot be accurately known or controlled.
- The RoboRoach system modulates frequency and amplitude, but not the current directly.
- This design accounts for biological variability while maintaining safety.
More Information
For detailed circuit schematics and technical documentation about the RoboRoach backpack, please refer to the official PDF:
