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R-2R attenuator PCB layout question
R-2R attenuator PCB layout question
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Old 13th January 2015, 08:22 PM   #21
OlegSh is online now OlegSh
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R-2R attenuator PCB layout question
Thanks for the offer! Now I know whom to ask if I fail to write my own code:-) I think writing the code should be a part of fun, unless it becomes a pain at some moment:-) I'll probably copy I2C expander / relay driver combo from your design if you don't mind... but on a separate board.
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Old 13th January 2015, 08:45 PM   #22
maxw is offline maxw  United Kingdom
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No worries, sounds good. Post pics when done.
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Old 14th January 2015, 05:48 PM   #23
OlegSh is online now OlegSh
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R-2R attenuator PCB layout question
I am now wondering what voltage relays to select for +5VDC supply? I assume there will be some voltage loss on the driver IC which is around 1 volt if I understand the datasheet right. Should I go with 4.5V relays or increase the supply voltage to meet 5V across the relay coils? The idea to run Arduino and the relays from the same supply would only work for 7V supply and above since Arduino comfortable supply range is 7~12 VDC and 20VDC being the maximum. This would require using 6V, 9V or even 12V relays depending on the actual supply voltage. Can't decide...
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Old 14th January 2015, 05:59 PM   #24
OlegSh is online now OlegSh
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R-2R attenuator PCB layout question
maxw, I just managed to recognize on one of the pictures in your thread that you used 5VDC relays without problems with the 5VDC supply. The Omron datasheet indicates the "must make" voltage as 80% of nominal (which is ~4VDC for 5VDC model). Do your relays work reliably or my estimate of the voltage drop across the driver IC is wrong? Or may be the relay can still work reliably at their edge?
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Old 15th January 2015, 08:18 AM   #25
maxw is offline maxw  United Kingdom
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I used a 5V PSU. The voltage drop across the ULN IC is about 1.2V IIRC. Basically, I just tested it and it worked. I think technically that voltage might be a bit low but I never had a problem with Omron G6K, AXICOM IM03 and AXICOM IM43 relays.
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Old 15th January 2015, 08:46 AM   #26
OlegSh is online now OlegSh
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R-2R attenuator PCB layout question
Thanks a lot maxw! You are really helping me here... I have very limited practical experience with all these, so your help is really appreciated!

I'll check if 4.5V relays are available at Mouser or Digikey. I'll probably take them instead of 5V parts just "in case":-) The idea to use a 5V supply is very attractive. Did you power the Arduino from the same 5V power supply?
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Old 15th January 2015, 09:04 AM   #27
maxw is offline maxw  United Kingdom
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4.5V relays would be wise but they are harder to get. Yes I used the same PSU for the Arduino. No worries, happy to help
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Old 27th January 2015, 07:47 PM   #28
OlegSh is online now OlegSh
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R-2R attenuator PCB layout question
I have finally finished the attenuator board. I decided to move in/outs to one side as it has been suggested earlier in the thread. I also made the I2C relay driver board and the input selector board (see attached).
I'll send them for fabrication in the next days. If in the end everything will work I'll post gerber files here.

By the way, mouser has 4.5 VDC relays and the price is OK.

Oleg
Attached Images
File Type: png Attenuator.png (105.9 KB, 465 views)
File Type: png RelayDriver.png (136.8 KB, 397 views)
File Type: png InOutSelector.png (123.9 KB, 389 views)
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Old 27th January 2015, 07:57 PM   #29
merlin2069er is offline merlin2069er  Canada
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Hey, that's great. If you were to interface it with a bleduino (BLEduino: Bluetooth 4.0 Made Easy) you can pair it with an bluetooth android app like this one.

https://play.google.com/store/apps/d...oremote.JGinfo

oh, you'd need to write a arduino sketch to turn the relays on / off.
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Old 27th January 2015, 08:04 PM   #30
OlegSh is online now OlegSh
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R-2R attenuator PCB layout question
So far the plan is to write an arduino code... but thanks for interesting suggestion. It would be cool to control the whole system from a smartphone. I'll have a closer look at bleduino.
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