On Tuesday, July 19, 2016 at 4:54:50 PM UTC+2, Jim Thompson wrote:> On Tue, 19 Jul 2016 09:38:11 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >On 07/18/2016 09:24 PM, George Herold wrote: > [snip]. > >> > >> Hey, I think it's a good idea for people who don't understand > >> TIA's and input C, to hang more on the inverting input and see > >> what happens. > > > >Yup. And then do the math so they understand why. It's just a few > >lines of algebra. Otherwise one might as well just wave a dead chicken > >over the circuit and fiddle till it sort of works. > > You forgot the most important "parts"... > > Eye of newt, and toe of frog, > Wool of bat, and tongue of dog, > Adder's fork, and blind-worm's sting, > Lizard's leg, and howlet's wing,-- > For a charm of powerful trouble, > Like a hell-broth boil and bubble.Macbeth (IV, i, 14-15) Shakespeare said it first. Jim may have learned it as his mother's knee (or some other low joint) but I suspect plagiarism. MIT graduates aren't famous for plagiarism but it does happen. -- Bill Sloman, Sydney
Phototransistor fed to a transimpedance amplifier
Started by ●July 17, 2016
Reply by ●July 19, 20162016-07-19
Reply by ●July 19, 20162016-07-19
On Mon, 18 Jul 2016 23:45:14 -0400, "Michael A. Terrell" <mike.terrell@earthlink.net> wrote:>Jim Thompson wrote: >> >> Are you trying out for the sound effects position for the next Batman >> and Robin movie ?>:-} > > > He would be 'Flatman', who is constantly being knocked out by high >voltage. ;-)Flatman and his side-kick Ribbon?
Reply by ●July 20, 20162016-07-20
"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message news:0JGdnZw_X6Hs3hPKnZ2dnUU7-LmdnZ2d@supernews.com...> Yeah, but yours is deep fried, which doesn't count. ;)What can I say? I'm a very philosophical monk. (A deep friar.) Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by ●July 21, 20162016-07-21
On 7/17/16 2:56 AM, SilverLeo wrote:> Hi all. > > I'm running through some test of a phototransistor signal conditioner, and I'm facing with wild noise issues. > The conditioning is a basic TIA stage: http://i.imgur.com/PcgglKZ.png > Feedback resistor is 5K, feedback capacitor is 470pF, negative bias is -12V, and photocurrent is in the range 8uA-800uA. The bandwidth should be about 50kHz. Opamp is OPA2277UA. > > Problem is that phototransistor if far away from TIA, with four meters of cable running along with power cables (valves, actuators, motors in the 5kW range). This causes tenth of uA of noise well inside the signal bandwith. > > The same phototransistor, with same cabling, works great with the simple resistor between collector and supply rail: http://i.imgur.com/Y1C2vEA.png > > TIA is better for me because it will keep phototransistor far away from saturation, but maybe the finite opamp bandwidth is actualy amplifying noise. > > Hints? > > >Just say no to analog light sensors on long cables. Go to mouser, search for this: taos Optical Detectors and Sensors Good Luck. -- Best Regards, ChesterW +++ Dr Chester Wildey Founder MRRA Inc. Electronic and Optoelectronic Instruments MRI Motion, fNIRS Brain Scanners, Counterfeit and Covert Marker Detection Fort Worth, Texas, USA www.mrrainc.com wildey at mrrainc dot com
Reply by ●July 21, 20162016-07-21
On 07/21/2016 04:52 PM, ChesterW wrote:> On 7/17/16 2:56 AM, SilverLeo wrote: >> Hi all. >> >> I'm running through some test of a phototransistor signal conditioner, >> and I'm facing with wild noise issues. >> The conditioning is a basic TIA stage: http://i.imgur.com/PcgglKZ.png >> Feedback resistor is 5K, feedback capacitor is 470pF, negative bias is >> -12V, and photocurrent is in the range 8uA-800uA. The bandwidth should >> be about 50kHz. Opamp is OPA2277UA. >> >> Problem is that phototransistor if far away from TIA, with four meters >> of cable running along with power cables (valves, actuators, motors in >> the 5kW range). This causes tenth of uA of noise well inside the >> signal bandwith. >> >> The same phototransistor, with same cabling, works great with the >> simple resistor between collector and supply rail: >> http://i.imgur.com/Y1C2vEA.png >> >> TIA is better for me because it will keep phototransistor far away >> from saturation, but maybe the finite opamp bandwidth is actualy >> amplifying noise. >> >> Hints? >> >> >> > Just say no to analog light sensors on long cables. Go to mouser, search > for this: > > taos Optical Detectors and Sensors > > Good Luck. >A phototransistor you can bypass. You really think I2C over 4 metres of cable is an improvement? You're definitely a sport. ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 22, 20162016-07-22
On 7/21/16 5:17 PM, Phil Hobbs wrote:> On 07/21/2016 04:52 PM, ChesterW wrote: >> On 7/17/16 2:56 AM, SilverLeo wrote: >>> Hi all. >>> >>> I'm running through some test of a phototransistor signal conditioner, >>> and I'm facing with wild noise issues. >>> The conditioning is a basic TIA stage: http://i.imgur.com/PcgglKZ.png >>> Feedback resistor is 5K, feedback capacitor is 470pF, negative bias is >>> -12V, and photocurrent is in the range 8uA-800uA. The bandwidth should >>> be about 50kHz. Opamp is OPA2277UA. >>> >>> Problem is that phototransistor if far away from TIA, with four meters >>> of cable running along with power cables (valves, actuators, motors in >>> the 5kW range). This causes tenth of uA of noise well inside the >>> signal bandwith. >>> >>> The same phototransistor, with same cabling, works great with the >>> simple resistor between collector and supply rail: >>> http://i.imgur.com/Y1C2vEA.png >>> >>> TIA is better for me because it will keep phototransistor far away >>> from saturation, but maybe the finite opamp bandwidth is actualy >>> amplifying noise. >>> >>> Hints? >>> >>> >>> >> Just say no to analog light sensors on long cables. Go to mouser, search >> for this: >> >> taos Optical Detectors and Sensors >> >> Good Luck. >> > > A phototransistor you can bypass. You really think I2C over 4 metres of > cable is an improvement? You're definitely a sport. ;) > > Cheers > > Phil HobbsI was thinking of something more like this: http://www.mouser.com/ds/2/588/TCS310x-519205.pdf It has a chance of fitting into the available space. The frequency output is probably a better choice for running with the motor cables than an analog signal. Also, you get a free spectrometer, so you can filter by color. Who was it who said never, never put a photo detector on the end of a cable? :) -- Best Regards, ChesterW
Reply by ●July 22, 20162016-07-22
>I was thinking of something more like this:>http://www.mouser.com/ds/2/588/TCS310x-519205.pdf>It has a chance of fitting into the available space. The frequency >output is probably a better choice for running with the motor cables >than an analog signal. Also, you get a free spectrometer, so you can >filter by color.>Who was it who said never, never put a photo detector on the end of a >cable? :)Same guy who said "never use a phototransistor for anything". ;) But the OP's application seems to be very low speed, so a barefoot phototransistor plus heavy bypassing should work fine. A 100-ms time constant gets rid of a lot of nasties. Cheers Phil Hobbs
Reply by ●July 22, 20162016-07-22
On 7/22/16 1:22 AM, Phil Hobbs wrote: <snip>> > Same guy who said "never use a phototransistor for anything". ;)I know. At first I wondered if you had been kidnapped and were trying to embed secret messages for help. I'm glad you're OK. If a lot of phototransistors were all in a pile, it might make a good paperweight. Maybe pour over with clear epoxy?> > But the OP's application seems to be very low speed, so a barefoot phototransistor plus heavy bypassing should work fine. A 100-ms time constant gets rid of a lot of nasties. > > Cheers > > Phil Hobbs >Hmmmm, maybe. Even running 110V for instrument power through trays with motor power is chancy, much less small signals. I got a paid trip to the Aleutians once because a PE broke that rule. Hey OP, u some place interesting? U use cable, I come fix. ChesterW
Reply by ●July 22, 20162016-07-22
On 07/22/2016 05:07 PM, ChesterW wrote:> On 7/22/16 1:22 AM, Phil Hobbs wrote: <snip> >> >> Same guy who said "never use a phototransistor for anything". ;) > > I know. At first I wondered if you had been kidnapped and were trying > to embed secret messages for help. I'm glad you're OK. > > If a lot of phototransistors were all in a pile, it might make a > good paperweight. Maybe pour over with clear epoxy?Personally I'd probably burn them for winter warmth. ;)> >> >> But the OP's application seems to be very low speed, so a barefoot >> phototransistor plus heavy bypassing should work fine. A 100-ms >> time constant gets rid of a lot of nasties. >> > > Hmmmm, maybe. Even running 110V for instrument power through trays > with motor power is chancy, much less small signals.Yeah, VFDs are seriously bad neighbours. You can get millivolts of crud across solid metal frames that are probably down in the microohms. Circulating current of some amperes, with millivolt drops, is what make ground loops so seemingly mysterious. Jiggling a wire changes the contact resistance and effectively makes or breaks the ground loop. Nickel-plated connectors make this much worse, because they form Ni-NiO-Ni tunnel junctions.> I got a paid trip to the Aleutians once because a PE broke that > rule.Did you get to visit Spruce Island? I hope to do that one day. I've only been as far as Homer. Terrific place in the summer.> > Hey OP, u some place interesting? U use cable, I come fix.It's supposed to be 114 in Riyadh tomorrow. ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 22, 20162016-07-22
On Fri, 22 Jul 2016 17:21:21 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 07/22/2016 05:07 PM, ChesterW wrote: >> On 7/22/16 1:22 AM, Phil Hobbs wrote: <snip> >>> >>> Same guy who said "never use a phototransistor for anything". ;) >> >> I know. At first I wondered if you had been kidnapped and were trying >> to embed secret messages for help. I'm glad you're OK. >> >> If a lot of phototransistors were all in a pile, it might make a >> good paperweight. Maybe pour over with clear epoxy? > >Personally I'd probably burn them for winter warmth. ;) > >> >>> >>> But the OP's application seems to be very low speed, so a barefoot >>> phototransistor plus heavy bypassing should work fine. A 100-ms >>> time constant gets rid of a lot of nasties. >>> >> >> Hmmmm, maybe. Even running 110V for instrument power through trays >> with motor power is chancy, much less small signals. > >Yeah, VFDs are seriously bad neighbours. You can get millivolts of crud >across solid metal frames that are probably down in the microohms. >Circulating current of some amperes, with millivolt drops, is what make >ground loops so seemingly mysterious. Jiggling a wire changes the >contact resistance and effectively makes or breaks the ground loop. >Nickel-plated connectors make this much worse, because they form >Ni-NiO-Ni tunnel junctions. >This is the VFD for a vent fan on the roof. It was making 20 volt spikes on the other side of the building. It was a nuisance to filter. https://dl.dropboxusercontent.com/u/53724080/Circuits/Filters/Filter.JPG -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
