An optically coupled power stimulus isolation unit with high voltage and fast rise time output

Abstract

Recent technological developments have created new devices that could improve and simplify the construction of stimulus isolators. HEXFET transistors can switch large currents and hundreds of volts in nanoseconds. The newer opto-isolators can give a pulse rise time of a few nanoseconds, with output compatible with MOSFET devices, in which delays are reduced to nanoseconds. Integrated DC/DC converters are now available. Using these new resources we developed a new electrical stimulus isolator circuit with selectable constant-current and constant-voltage modes, which are precise and easy to construct. The circuit works like a regulated power supply in both modes with output switched to zero or to free mode through an opto-isolator device. The isolator analyses showed good practical performance. The output to ground resistance was 10 11 ohms and capacitance 35 picofarads. The rise time and fall time were identical (5 µs) and constant. The selectable voltage or current output mode made it very convenient to use. The current mode, with higher output resistance values in low current ranges, permits intracellular stimulation even with tip resistances close to 100 megaohms. The high compliance of 200 V guarantees the value of the current stimulus. The very low output resistance in the voltage mode made the device highly suitable for extracellular stimulation with low impedance electrodes. Most importantly, these characteristics were achieved with a circuit that was easy to build and modify and assembled with components available in Brazil. Correspondence

StimDuino: An Arduino-based electrophysiological stimulus isolator

“…2A), we used the simplified design of Brasil and Leal-Cardoso (1999). The original design included the possibility for different modes of stimulation: (a) controlling the current (constant current mode), (b) controlling the voltage (constant voltage mode), (c) stimulation mode in which the user can adjust both the voltage and the current ("automatic" mode) (Brasil and Leal-Cardoso, 1999). Since the constant current is the preferable mode of stimulation for electrophysiological experiments (brain slice and in in vivo field potential recordings), we omitted the possibility of constant voltage and "automatic" modes.…”

“…2 and 4 step 7) and the voltage drop on the shunt resistor (Fig. 4, step 6) are read from the Arduino Uno analog ports (potentiometer reference voltage from pin A0 defined as 'sensorPin'; shunt voltage from pin A1 defined Brasil and Leal-Cardoso (1999). The digital part shows the connection of the Arduino UNO to the A4988 stepper motor driver, bipolar stepper motor and relays (RL1 and its switching contacts, RL1.1, RL1.2 are depicted in red, RL2 and its switching contacts are depicted in green).…”

“…Among the presented devices (Table 1), only A365 (World Precision Instruments, FL, USA) stimulus isolator complies with the requirements of the electrophysiological experiments. As alternative solution to the commercial stimulus isolators, several low cost customized devices have been proposed previously (Baird, 1967;Brasil and Leal-Cardoso, 1999;Land et al, 2004;Millar and Barnett, 1988;Millar et al, 1994). Among these devices, the stimulus isolator of Brasil and Leal-Cardoso (1999) provides an excellent solution to many electrophysiological applications: high (up to 200 V) compliance, the ability to operate in constant current or constant voltage mode, short (about 5 s) rise time of the applied stimulus (and, as a result, brief stimulation artifact).…”

“…However, the implementation and programming of microcontrollers could be beyond the abilities of students or researchers with a minimal knowledge of digital electronics. Here, we describe a personal computer (PC)-controlled, Arduinointegrated modification of the stimulator of Brasil and Leal-Cardoso (1999) -the StimDuino, developed in our laboratory and designed to overcome the abovementioned shortcomings of the available commercial and customized stimulators. Arduino is a flexible, open-source electronics platform designed to build and control a wide spectrum of devices, which interact with the environment.…”

Universal serial bus powered and controlled isolated constant-current physiological stimulator

“…Other custom stimulators that produce constant voltage, and constant voltage and small constant currents, were described by Land et al 1 and Brasil et al, 2 respectively, among others. Both of these stimulators are geared toward pacing or single pulse generation.…”