UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Reverse engineering Lumenition optical switch

Uncle Bulgaria · 8th May 2020, 8:03 pm

Thanks, Chris! That's very interesting to see the power module in bits, too.

As you can see in my initial post, my two optical bits are obviously different colours. However, either I recorded them entirely wrongly or in this case the LED and the detector are reversed (detector clear, LED orange) as there will be no emission if 7.5V is across the LED and the 5k resistor, as my circuit surmise suggested. I've had some work to do today, but have been attempting to draw out the circuit while looking at open collectors (thanks, Eddie and RadioWrangler!) and opto-couplers for ideas as to what the SMT components might be. The values of 250R and 5K appear in line with optical coupling circuits I've looked at, so I'm feeling confident I can work it out with a bit of SPICE modelling and some veroboard. I'm going to use other Chris's suggestion of battery and resistor to test the LED as well. My diode test is inconclusive, so I'll check the camera option.

Your dissection of the power module is helpful, as it suggests that I could rebuild this with through-hole components (I have no stocks or experience of SMD) before re-potting.

8th May 2020, 8:03 pm	#16
Uncle Bulgaria Nonode Join Date: May 2016 Location: Cornwall, UK. Posts: 2,330	Re: Reverse engineering Lumenition optical switch Thanks, Chris! That's very interesting to see the power module in bits, too. As you can see in my initial post, my two optical bits are obviously different colours. However, either I recorded them entirely wrongly or in this case the LED and the detector are reversed (detector clear, LED orange) as there will be no emission if 7.5V is across the LED and the 5k resistor, as my circuit surmise suggested. I've had some work to do today, but have been attempting to draw out the circuit while looking at open collectors (thanks, Eddie and RadioWrangler!) and opto-couplers for ideas as to what the SMT components might be. The values of 250R and 5K appear in line with optical coupling circuits I've looked at, so I'm feeling confident I can work it out with a bit of SPICE modelling and some veroboard. I'm going to use other Chris's suggestion of battery and resistor to test the LED as well. My diode test is inconclusive, so I'll check the camera option. Your dissection of the power module is helpful, as it suggests that I could rebuild this with through-hole components (I have no stocks or experience of SMD) before re-potting.