Photodiodes & phototransistors should be much faster than=20 photoresistors, so cleaner edges. I believe photodiodes have the=20 fastest transistions so a schmitt trigger may not be needed (other than=20 the I/P of the microcontroller). I like this project idea... would be nice to see how things change as my=20 3D printer, fridge, A/C, etc comes on, without having to move around a=20 plug-in power monitor. Cheers, -Neil. On 2/20/2018 5:34 AM, Clint Jay wrote: > In all the energy monitor projects I remember seeing I've not seen a CdS > cell used, not that I think there is anything wrong with that idea, they'= ve > all used a phototransistor or photodiode, I seem to remember one that use= d > an LED... > > The late John Becker had one or two published in EPE that were Pic based, > might be worth seeking those out? > > On 20 Feb 2018 10:29, "David C Brown" wrote: > >> This is one of those so trivial problems that shouldn't need advice but,= as >> so often with me, I have over researched to the point where Ic an't make= a >> decision. >> >> Since I am not going to get a smart electricity meter real soon now I >> intend to build my own power monitor. The meter has a red LED which >> flashes 1000 times per kWh and the key to the project is measuring the t= ime >> between flashes. >> >> But I can't decide the best way to detect the flashing LED. CDS photo >> resistor followed by a Schmit trigger; photo transistor followed by a >> transimpedance amp. There should be no problem excluding ambient light >> and the LED flashes for about 1/2 second. >> __________________________________________ >> David C Brown >> 43 Bings Road >> Whaley Bridge >> High Peak Phone: 01663 733236 >> Derbyshire eMail: dcb.home@gmail.com >> SK23 7ND web: www.bings-knowle.co.uk/dcb >> >> >> >> >> *Sent from my etch-a-sketch* >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .