Author Topic: Optically Isolated USB-UART adapter  (Read 3475 times)

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Offline Emil

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Optically Isolated USB-UART adapter
« on: December 02, 2017, 11:17:41 am »
Hi,

I launched a Kickstarter campaign yesterday for my optically isolated USB to UART adapter.

https://www.kickstarter.com/projects/902741881/optically-isolated-usb-to-serial-adapter

  • 1.8V to 5V logic levels
  • 300 baud to 2Mbaud
  • 2500V isolation

Overything except the board layout/gerber files are open source. I'm using Dave's version of the gear logo with letters: https://www.eevblog.com/forum/blog/eevblog-921-open-source-hardware-problems-solved!/

 

Offline Emil

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Re: Optically Isolated USB-UART adapter
« Reply #1 on: December 30, 2017, 11:05:04 am »
Dave's latest mailbag shows my adapter :)  EEVBlog #1049 - Mailbag https://youtu.be/eBzixNYF5K4
 

Offline mikeselectricstuff

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Re: Optically Isolated USB-UART adapter
« Reply #2 on: December 30, 2017, 11:16:35 am »
Pity you didn't use the pretty-much-standard TTL232 header pinout for compatibility with existing devices
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Online nctnico

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Re: Optically Isolated USB-UART adapter
« Reply #3 on: January 01, 2018, 01:41:16 pm »
I'd like to see these kind of products in a standard casing instead of just another loose board. Please don't start with 3D printing because that isn't an off-the-shelve solution you can scale up to larger volumes easely.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Emil

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Re: Optically Isolated USB-UART adapter
« Reply #4 on: January 01, 2018, 01:54:43 pm »
Pity you didn't use the pretty-much-standard TTL232 header pinout for compatibility with existing devices

I didn't realize that there was a pinout that was common enough to be considered standard, so I just used a pinout I thought would be practical.
 

Offline Emil

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Re: Optically Isolated USB-UART adapter
« Reply #5 on: January 01, 2018, 02:22:16 pm »
I'd like to see these kind of products in a standard casing instead of just another loose board. Please don't start with 3D printing because that isn't an off-the-shelve solution you can scale up to larger volumes easely.

Just to clarify, I'm not planning to sell 3D printed cases for the adapter, just provide files which people can print as is or modify to suit their needs.

There is a few different reasons I didn't include a case: I think many people will use it without a case so the extra cost would be wasted for them. I don't know what kind of connector people prefer on the device side, so I would need to provide several with the extra logistics issued that implies, or go with one and possibly make something many people don't want. There is also the issue of longer time to market when getting enclosures with punched/milled holes for connectors, since it would take a round or two with prototypes from an enclosure manufacturer. I really didn't know if the adapter would be popular or flop completely, so the extra time and cost didn't seem worth it.

Since there has been more interest than I was expecting, a future version with an enclosure is a possibility. I'm very interested in hearing from you and others what kind of form factor and device side connector you prefer.
 

Online nctnico

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Re: Optically Isolated USB-UART adapter
« Reply #6 on: January 01, 2018, 02:37:15 pm »
This is one of my products which is similar to yours: a ruggedized USB to TTL serial converter (which can also serve as an NXP ARM microcontroller programmer and it has RS485 too). The case is standard but the front & rear panels are lasercut aluminium. I (reluctantly) designed it because there was nothing like it on the market and I didn't want to deliver boards wrapped in heat shrink tubing to my customers.
« Last Edit: January 01, 2018, 02:41:32 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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Offline luftek

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Re: Optically Isolated USB-UART adapter
« Reply #7 on: January 01, 2018, 06:00:08 pm »
Thank you for sharing!

Maybe instead of CH340G
you use CH340C which does not need external crystal and is for some reason cheaper: https://lcsc.com/product-detail/USB_CH340C_C84681.html

According to document: http://www.wch.cn/downfile/79
C, B, E variants don't need external crystal

I agree designing according to enclosure constraints should be one of priorities. Large shrink wrap won't do it.
I recommend something like:
https://www.aliexpress.com/item//32805387296.html 3€/5pcs but probably something smaller would do

 
 

Offline phil from seattle

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Re: Optically Isolated USB-UART adapter
« Reply #8 on: January 01, 2018, 06:19:37 pm »

According to document: http://www.wch.cn/downfile/79
C, B, E variants don't need external crystal
Is there an English translation of that document?
 

Online nctnico

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Re: Optically Isolated USB-UART adapter
« Reply #9 on: January 01, 2018, 06:21:20 pm »
I agree designing according to enclosure constraints should be one of priorities. Large shrink wrap won't do it.
I recommend something like:
https://www.aliexpress.com/item//32805387296.html 3€/5pcs but probably something smaller would do
I wouldn't because it needs milling/drilling. An enclosure with panels you can replace with lasercut panels or PCB material is ideal for quick assembly.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline luftek

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Re: Optically Isolated USB-UART adapter
« Reply #10 on: January 01, 2018, 07:18:51 pm »
Depends on design. Yes PCB as front/rear panel is really handy. Have used it before.

Better optical isolator ??:
https://www.ebay.com/itm/USB-to-TTL-UART-RS232-Isolated-FT230-5V-3-3V-2-5V-1-8V/173023438576
seems MAX12931 can do 1.8V out of the box?
https://www.maximintegrated.com/en/products/MAX12931
 
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Offline voltsandjolts

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Re: Optically Isolated USB-UART adapter
« Reply #11 on: January 01, 2018, 07:24:00 pm »
@nctnico

May I ask, where did you source that case?
 

Offline Emil

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Re: Optically Isolated USB-UART adapter
« Reply #12 on: January 01, 2018, 08:25:44 pm »
Maybe instead of CH340G
you use CH340C which does not need external crystal and is for some reason cheaper: https://lcsc.com/product-detail/USB_CH340C_C84681.html

According to document: http://www.wch.cn/downfile/79
C, B, E variants don't need external crystal

I have been using the CH340G for a few projects, but I wasn't aware of the CH340C, maybe because I haven't found a datasheet in English. Thank you for the suggestion.

Looks like C and B should be drop in compatible on my board, but I would of course need to test that.

Have you tried the CH340 parts without crystal? I think oscillator accuracy/stability is critical for USB, so if it's got an internal RC oscillator it would need to be a really good one(?)
 

Online Jeroen3

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Re: Optically Isolated USB-UART adapter
« Reply #13 on: January 01, 2018, 08:33:55 pm »
Great board!

I've made a dozen of those boards myself years ago as well. Using FT230X and Si8642, with the typical FTDI header.
They have proven to be very useful and robust.

I never bothered to commercialize them. Maybe I should as well...
 

Offline Kjelt

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Re: Optically Isolated USB-UART adapter
« Reply #14 on: January 01, 2018, 08:40:50 pm »
I use so many different usb adapters, like 3v3 ttl, 5v ttl, , rs485 and 232 so I bought an USB isolator to put in front. Only problem us the bandwith limitation, the stm8 serial link which is aprox 10MHz does nit work.
 

Online 0xdeadbeef

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Re: Optically Isolated USB-UART adapter
« Reply #15 on: January 01, 2018, 08:41:41 pm »
Did something like this as well some time ago and found the PACTEC CNS-0407 to be a fitting off-the-shelf case. I used an USB-B connector though.
Trying is the first step towards failure - Homer J. Simpson
 

Offline Emil

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Re: Optically Isolated USB-UART adapter
« Reply #16 on: January 01, 2018, 10:29:23 pm »
Just a heads up. The Kickstarter campaign ends in 30 minutes.
 

Offline Sjokolade

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Re: Optically Isolated USB-UART adapter
« Reply #17 on: January 01, 2018, 11:23:59 pm »
Can I choose between micro usb and type B connector ?
If at first you do succeed try not to look astonished
 

Offline Emil

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Re: Optically Isolated USB-UART adapter
« Reply #18 on: January 02, 2018, 06:28:21 pm »
Can I choose between micro usb and type B connector ?

Yes, you can choose. There will be a survey before I ship the boards.
 

Online nctnico

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Re: Optically Isolated USB-UART adapter
« Reply #19 on: January 04, 2018, 06:07:39 pm »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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Offline Atika

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Re: Optically Isolated USB-UART adapter
« Reply #20 on: January 06, 2018, 10:57:22 pm »
Depends on design. Yes PCB as front/rear panel is really handy. Have used it before.

Better optical isolator ??:
https://www.ebay.com/itm/USB-to-TTL-UART-RS232-Isolated-FT230-5V-3-3V-2-5V-1-8V/173023438576
seems MAX12931 can do 1.8V out of the box?
https://www.maximintegrated.com/en/products/MAX12931

Thank you for sharing our debug board on eBay store!! We inspired and launched our new version of debug board on kickstarter as well. Here is our test with 220VAC main:
 
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