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• Battery Isolator:  This circuit uses a few p-channel power FETs and a new IC from Linear Technology.  It allows an alternator to charge two different lead-acid batteries but isolates the individual battery loads, so that loads on one battery do not draw power from the other battery.  This configuration is often used on recreational vehicles.  It is rated at 28v and up to 50 amps

• Fully Isolated 50/60Hz Sync Generator
  This circuit will produce a single pulse at the zero voltage cross points of the power line voltage.  An opto-coupler provides a very safe 5KV isolation.

• HONEYBEE COUNTER
  I designed a circuit similar to this one a long time ago to help a beekeeper count the number of bees going into or out of a hive. The low power circuit uses a slotted opto-sensor to detect the passing bees. The circuit advances an electronic counting module whenever a honeybee passes through the sensor. The device only counts the number of bees going through the sensor. A different circuit would be needed to count the number of bees only going out or only coming into the hive.

• MACHINE POWER LOSS BEEPER
  For some medical equipment it is important for an operator when power is lost to the machine. The beeper is powered from a 9v battery and requires the machine to have a power switch with a third set of contacts.

• Negative 0.5 Volt Supply 
  With the component values shown, this simple circuit will provide a negative 0.5 volts at about 2 milliamps.  It is perfect for rail to rail op amp circuits, where a true 0 volt output is needed.

Analog Opto Isolator:  (circuit / schematic added 2/03)

Battery Powered Amplifier has Optical Isolation:  06/06/96 EDN Design Ideas  / (added 6/03)  When you interconnect scientific instruments, especially older ones, you often need both gain and galvanic isolation for the analog interface functions.

Circuit compensates optocoupler temperature coefficient:  11/22/01 EDN Design Ideas  /  (added 1/05)  When using an optocoupler in a linear application, you should consider its gain drift with temperature. Traditional single- and dual-transistor-output devices have a notable gain drift with temperature. In recent years, some temperature-compensated optocouplers have appeared. However, another option is to use two optocouplers or a dual optocoupler with appropriate feedback to make the dri... ...

Circuit Protects Computer's Input:  05/26/94 EDN-Design Ideas  / (Electronic Circuit diagram added 03/03)   The circuit in Fig 1 performs input protection, level translation, isolation, and debouncing. The circuit allowed the output of a relay driver to connect to a computer even though the relay driver delivered a voltage as high as 24V and the relay driver had no ground connection. With the values in Fig 1 the low and high thresholds at the circuit's input were approximately 8 and 16V, respectively. The cutoff frequency was high enough to allow counting 1200 counts/min. The input withstood 110V ac continuously—the optoisolater's withstand voltage is 3 kV. I tested the debouncing function with a microswitch....    

Circuit Widens octocoupler's Response to 1 MHz:  12/21/95 EDN-Design Ideas / (Electronic Circuit diagram added 03/03)

Drive High Voltage Varactor Diodes From just 5V:  03/27/97 EDN-Design Ideas / (Electronic Circuit diagram added 03/03)   -- How to connect two International Rectifier (El Segundo, CA) PVI1050s photovoltaic-isolator ICs in series to provide a20-Volt tuning drive for the varactor diode

Light Powers Isolation Amplifier:  01/21/99 EDN-Design Ideas  / (added 11/05)  Self-powered isolation amplifiers, which need no external isolated power supply, provide versatile and convenient interfaces in many applications that require galvanic isolation of the signal source. Examples of such applications include circuits that serve in industrial or medical environments, in which isolation is necessary for noise reduction or safety. You can use a variety of isolated signal-coupling techniques for the signal paths of these amplifiers. Transformers, differential-capacitor, and opto- isolator schemes are all popular choices. For the internal isolated power supply, transformer coupling is virtually universal, despite the problems inherent in inductively coupled circuits. These problems include relatively high interwinding stray capacitance and a tendency to couple switching noise into the signal. In contrast, the self-powered amplifier in Figure 1 is different in that it incorporates optoisolators to effect communication of both signal and power around the isolation barrier....