Description:   
The Model 4D Digital Stimulus Isolation Amplifier (SIU) is a low-noise optical isolation amplifier design to optically isolate electrical stimulating currents.  

Highlights:   
ZERO leakage current, high compliance (72 VDC), ZERO power on spikes (maintains short circuit across electrode when off), battery load test function, good step response.  

Theory of operation:  
Inputs: The input mode is digital. TTL or CMOS 0V to 5V. Input connector is isolated BNC.  
Output: Output is a current source. Therefore unit operates as a Digitally controlled Current Source. Output connector is also an isolated BNC.  
Range: Three output ranges are 0-0.1mA, 0-1mA or 0-10mA. The output is adjust with a 10-turn potentiometer where the value of the pot reflects the value of the output current when a digital pulse is applied. e.g. when the range is 0-1mA and the pot is set at 6 turns the output current will be 0.6mA during the time that the digital input is at a "high" logic level. The range is set from a three position toggle switch.  
Power: Powered by 10 9Volt alkaline batteries.