This message was in the PICList discards list - and there seem to be quite a few other valid ones there just recently as well. This message does not SEEM to have turned up on list other than this version )sometimes there is a discarded and an accepted version for some reason). So I'll post it and people can tell me why I shouldn't have. Are people finding that their messages are going missing more than usual just lately? Olin reported one and therte look to be others. Comments welcome. Russell _________________________________ ----- Original Message ----- From: "Michael Algernon" To: "Microcontroller discussion list - Public." Sent: Saturday, November 22, 2008 8:08 PM Subject: [EE]: DIY opto-isolator furrgetaboutit I have built a do-it-yourself opto-isolator using twoT13/4 red LEDs pointing at each other. Thanks to suggestions from the PIClist , it occurred to me to add a 2N4401 transistor to the circuit to increase the current gain. I used a 74C14 ( CMOS hex inverter with schmitt triggers ) to make an oscillator and a detector. This is only useful to automate turning the driving LED on and off. see http://oh-god.com:5080/dir/diy-optoiso/ 001.jpg is the schematic. I used RsubF and CsubF to set the period for an on-off oscillator at about 1Hz. RsubL is 1K ohms. V+ is 7 volts. So about 5ma is going thru the LED on the left. RsubB is 100K ohms. And it works ! yeaaaa. 002.jpg shows an out of focus photo of the breadboard. Used a MacBook and the PhotoBooth application. The silver thingie consists of the two LEDs glued ( superglue gel ) together facing each other and coated with silver paint. I thought the paint might block external light and maybe reflect internal light. The 2N4401 has a red blob on it and the 74C14 is to the right. I used 1K ohm resistors for zero ohm jumpers where 1K ohm was essentially zero in the circuit. 003.jpg shows the silver thingie thru a magnifying glass. I plan to use spare inverters on the 74C14 to differentially drive small transformer at 100KHz. The rectified DC voltage on the other side of the transformer will be regulated by the opto-isolator turning off the 100KHz oscillator when the voltage is high enough. Thus I achieve a low current isolated DC supply for my truck to power $2 DMMs I bought at Harbor Freight. The DMMs don't work unless they are isolated from the truck ground. MA WFT Electronics Denver, CO 720 222 1309 " dent the UNIVERSE " All ideas, text, drawings and audio , that are originated by WFT Electronics ( and it's principals ), that are included with this signature text are to be deemed to be released to the public domain as of the date of this communication . -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist