msi1259 wrote: > Years ago, I worked on a ECG pickup that vibrated about a 3" diameter > piezo-electric disk by applying a frequency to the outer diameter and > connections to the center of the disk were rectified to power the > patient side of the ECG leads. I think the designer had previously > worked on Sonar. > > John Snider > > Forrest Christian wrote: > >> >> So, the question is this: Is there such a beast? That is a truly >> isolated relay closure input which does not require a separate power >> supply on the relay side - oh and one final requirement, it has to be at >> least somewhat reasonably inexpensive >> >> > > These devices are easily confused with standard opto-isolators. These devices are actually photovoltaic devices. Their input is a small current driving an IR emitter, but the internal secondary is a series of PV cells wired in series so that the output is a voltage. The voltage is dependent on the current of the input, but on most devices it ranges from 3 to 30VDC. The rub is that the output current is almost NIL, but it will drive FETs directly. Look at Digikey's P/N TLP191BF-ND; it is a fine device that I use frequently, made by Toshiba, the TLP191B. While its spec indicates 7V, driving 5V thru a 330-ohm resistor at the input gives a 20+ volt output, enough to drive any MOSFET I know of. Costs $2.70 USD in singles. --Bob Axtell -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist