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low cost isolation amplifier

Started by Unknown November 18, 2021
On a sunny day (Thu, 18 Nov 2021 13:33:06 -0500) it happened Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote in
<46c805fc-43c4-7fb6-2c80-791b6b2c29d4@electrooptical.net>:

>whit3rd wrote: >> On Thursday, November 18, 2021 at 8:11:22 AM UTC-8, Phil Hobbs wrote: >>> Phil Hobbs wrote: >> >>>> TI used to make the (iirc) TIL311, >>> TIL300, it was. >>>> which had a LED and two photodiodes, all mutually isolated. You used >>>> one PD to servo the LED brightness, and used the other one as the >>>> output. >> >> I'd consider using a dual isolator, with the LEDs in series, >> except that the usual pinouts don't physically separate the >> hot-side output from the cold one. It'd be OK for low-voltage floating, though. >> >> TIL300 matching (transfer gain) is tested, the -A version had max 10% mismatch, >> with 25% on the run-of-the-mill parts. That probably is a production nuisance. >> > >Well, the part is long gone anyway. > >Cheers > >Phil Hobbs
An other way was use two 4046 chips, FM modulate the first one with audio on pin 9 I think it was, VCO out pin 4 to fast optocopler LED. other end: photo diode to second 4046 signal in pin 14 and have the thing in PLL mode. VCO out pin 4 to pin 3 XOR phase comparator. Loop filter, control voltage to pin 9 is your audio out. Also seventies. In the sixties for video I used 2 74121 as FM modulator driving the C via a current source.... about 7 MHz carrier I think it was any non galvanic coupling you like and any fM demodulator you like (was replacing an Ampex modulator with tubes in that experiment). You could use a 64 us PAL glass delay line, modulate some way some carrier at 4.43 MHz, pick it up on the receiver side piezo.. Only did it for video. https://upload.wikimedia.org/wikipedia/commons/5/5e/Us_delay_line.jpg so basically acoustic in gals, glass is a good isolator. Speaker and mike works too come to think of it ;-) The sound of a modem tcm3105 comes to mind... For very low speeds you could use smell, https://newsroom.intel.com/news/how-computer-chip-smell-without-nose/#gs.gbfp1l mm maybe air pressure changes in a plastic pipe would work too Just getting carried away a bit here..
On 2021-11-18, Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:
> torsdag den 18. november 2021 kl. 19.43.52 UTC+1 skrev bitrex: >> On 11/18/2021 1:38 PM, bitrex wrote: >> > On 11/18/2021 12:02 PM, Dimiter_Popoff wrote: >> >> On 11/18/2021 7:28, jla...@highlandsniptechnology.com wrote: >> >>> On Thu, 18 Nov 2021 00:00:46 -0500, bitrex <us...@example.net> wrote: >> >>> >> >>>> On 11/17/2021 11:19 PM, jla...@highlandsniptechnology.com wrote: >> >>>>> >> >>>>> https://www.mouser.com/ProductDetail/Texas-Instruments/ISO120SG?qs=rNOSrj6uCs17dA0jO5%2FyAw%3D%3D >> >>>>> >> >>>>> >> >>>>> >> >>>>> >> >>>> >> >>>> They had to pay the burglars to snatch some out of the Smithsonian so >> >>>> they could put them back on the shelf >> >>> >> >>> But I really need a low cost isolation amplifier. >> >>> >> >>> Looks like roughly $3 each. SiLabs has a three channel isolated ADC >> >>> that is interesting, if I can figure out the actual throughput rate. >> >>> Si8902. >> >>> >> >> >> >> Depending on the throughput you need could you perhaps do some cheap >> >> ADC -> opto -> DAC scheme... I am not very familiar with the cheap side >> >> of MCU-s but I think there are very cheap ones with an ADC, not so >> >> sure about the DAC (those I use are precision, cost >$10, but may be >> >> there are cheaper). I suppose something like 10uS per word should >> >> be achievable but well, I am just musing. >> >> >> > >> > There are I2C isolators with 2.5kV standoff voltages, at 400kHz >> > signaling rate I think you should be able to get close to 60kHz 16 bit >> > data across that with some basic lossless compression like modems use >> It would be interesting project to see how good you could do with the 10 >> bit internal ADC and some data compression on say a ATTiny85 on one side >> and another doing decompress and fast PWM DAC on the other with both >> 8-bitters just running flat-out at 20 MHz top speed > > AD have several isolated delta-sigma ADCs that would just need a clock and a lowpass filter on the "DAC" side
Really? all you people with your helpful suggestions! LOL. I interpreted the original message as Look what I found on the WWW and posted under a sarcastic subject line. -- Jasen.
On 11/18/2021 20:43, bitrex wrote:
> On 11/18/2021 1:38 PM, bitrex wrote: >> On 11/18/2021 12:02 PM, Dimiter_Popoff wrote: >>> On 11/18/2021 7:28, jlarkin@highlandsniptechnology.com wrote: >>>> On Thu, 18 Nov 2021 00:00:46 -0500, bitrex <user@example.net> wrote: >>>> >>>>> On 11/17/2021 11:19 PM, jlarkin@highlandsniptechnology.com wrote: >>>>>> >>>>>> https://www.mouser.com/ProductDetail/Texas-Instruments/ISO120SG?qs=rNOSrj6uCs17dA0jO5%2FyAw%3D%3D >>>>>> >>>>>> >>>>>> >>>>>> >>>>> >>>>> They had to pay the burglars to snatch some out of the Smithsonian so >>>>> they could put them back on the shelf >>>> >>>> But I really need a low cost isolation amplifier. >>>> >>>> Looks like roughly $3 each. SiLabs has a three channel isolated ADC >>>> that is interesting, if I can figure out the actual throughput rate. >>>> Si8902. >>>> >>> >>> Depending on the throughput you need could you perhaps do some cheap >>> ADC -> opto -> DAC scheme... I am not very familiar with the cheap side >>> of MCU-s but I think there are very cheap ones with an ADC, not so >>> sure about the DAC (those I use are precision, cost >$10, but may be >>> there are cheaper). I suppose something like 10uS per word should >>> be achievable but well, I am just musing. >>> >>..... > > It would be interesting project to see how good you could do with the 10 > bit internal ADC and some data compression on say a ATTiny85 on one side > and another doing decompress and fast PWM DAC on the other with both > 8-bitters just running flat-out at 20 MHz top speed
Don't know the ATTiny but assuming they can do PWM at 20 MHz at 10 bits this would mean somewhat > 50us, not as bad as I intuitively would have assumed really. Filtering that will take its toll though, probably making it impractical (being after low cost). I was thinking more of a some "normal" DAC which is cheap enough and an MCU with an ADC driving it via some optocoupler. But like I said I don't know if there are any DACs that cheap, John is after low cost for this.
On Thu, 18 Nov 2021 10:56:03 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>torsdag den 18. november 2021 kl. 19.43.52 UTC+1 skrev bitrex: >> On 11/18/2021 1:38 PM, bitrex wrote: >> > On 11/18/2021 12:02 PM, Dimiter_Popoff wrote: >> >> On 11/18/2021 7:28, jla...@highlandsniptechnology.com wrote: >> >>> On Thu, 18 Nov 2021 00:00:46 -0500, bitrex <us...@example.net> wrote: >> >>> >> >>>> On 11/17/2021 11:19 PM, jla...@highlandsniptechnology.com wrote: >> >>>>> >> >>>>> https://www.mouser.com/ProductDetail/Texas-Instruments/ISO120SG?qs=rNOSrj6uCs17dA0jO5%2FyAw%3D%3D >> >>>>> >> >>>>> >> >>>>> >> >>>>> >> >>>> >> >>>> They had to pay the burglars to snatch some out of the Smithsonian so >> >>>> they could put them back on the shelf >> >>> >> >>> But I really need a low cost isolation amplifier. >> >>> >> >>> Looks like roughly $3 each. SiLabs has a three channel isolated ADC >> >>> that is interesting, if I can figure out the actual throughput rate. >> >>> Si8902. >> >>> >> >> >> >> Depending on the throughput you need could you perhaps do some cheap >> >> ADC -> opto -> DAC scheme... I am not very familiar with the cheap side >> >> of MCU-s but I think there are very cheap ones with an ADC, not so >> >> sure about the DAC (those I use are precision, cost >$10, but may be >> >> there are cheaper). I suppose something like 10uS per word should >> >> be achievable but well, I am just musing. >> >> >> > >> > There are I2C isolators with 2.5kV standoff voltages, at 400kHz >> > signaling rate I think you should be able to get close to 60kHz 16 bit >> > data across that with some basic lossless compression like modems use >> It would be interesting project to see how good you could do with the 10 >> bit internal ADC and some data compression on say a ATTiny85 on one side >> and another doing decompress and fast PWM DAC on the other with both >> 8-bitters just running flat-out at 20 MHz top speed > >AD have several isolated delta-sigma ADCs that would just need a clock and a lowpass filter on the "DAC" side >
We'll untimately want to acquire voltage and current from an isolated power supply or dummy load channel, and push that into an FPGA, so the deliverable is data. We would close some loops in the FPGA, like current and power limiting, and do waveform acquisition as a bonus feature, so I'd like at least 100K e/i pairs per second. It could just about be done with a uP on the high side, using its ADC. Move the current limits and such up there. If we could get delivery on uPs! We use the ADUM7703 isolated ADC in another product, and they are great, just a tad expensive for a high channel count system. I guess we could consider some tacky home-made PWM thing. -- If a man will begin with certainties, he shall end with doubts, but if he will be content to begin with doubts he shall end in certainties. Francis Bacon
On Thursday, November 18, 2021 at 11:46:27 AM UTC-8, Jan Panteltje wrote:

[about isolation amplifiers]

> You could use a 64 us PAL glass delay line, modulate some way some carrier at 4.43 MHz, pick it up on the receiver side piezo.. > Only did it for video. > https://upload.wikimedia.org/wikipedia/commons/5/5e/Us_delay_line.jpg > so basically acoustic in gals, glass is a good isolator. > > Speaker and mike works too come to think of it ;-)
And, don't forget power; if you want a half a megavolt of isolation for power, an ultrasonic transducer, half a meter of ceramic rod, and a second 'pickup' transducer can do the trick. That was for a van de Graaff apparatus...
On Thursday, November 18, 2021 at 4:28:59 PM UTC+11, jla...@highlandsniptechnology.com wrote:
> On Thu, 18 Nov 2021 00:00:46 -0500, bitrex <us...@example.net> wrote: > > >On 11/17/2021 11:19 PM, jla...@highlandsniptechnology.com wrote: > >> > >> https://www.mouser.com/ProductDetail/Texas-Instruments/ISO120SG?qs=rNOSrj6uCs17dA0jO5%2FyAw%3D%3D > >> > >> > >> > > > >They had to pay the burglars to snatch some out of the Smithsonian so > >they could put them back on the shelf > But I really need a low cost isolation amplifier. > > Looks like roughly $3 each. SiLabs has a three channel isolated ADC > that is interesting, if I can figure out the actual throughput rate. > Si8902.
My solution - back in 1975 - was a three-winding transformer. Two of the windings were made with fine wire, and used only for voltage feedback. I drove the high current winding to get the voltage I wanted to send on the feedback winding, and monitored the current I was pushing in. The isolated output was feed into a sample-and-hold amplifier, which got switched to "hold" whenever the drive current got too high and was being pulled back fast to an equal and opposite current in the other direction. The "hold" period was only a couple of milliseconds (which was fine for process control signals) and the whole set-up was cheap and remarkably accurate. A few years later, I shifted a twelve bit word across an isolation barrier as Manchester-2 serial string, using a small feritte toroid stapled to the board with six U-shaped bits of wire - three were the drive windings and the other three the sense windings. I used a comparator with hysteresis as the receiver. That was pretty cheap too. Sigma-delta A/D converters could give you a 20-bit word these days. -- Bill Sloman, Sydney