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R-2R attenuator PCB layout question
R-2R attenuator PCB layout question
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Old 12th January 2015, 05:53 PM   #11
OlegSh is offline OlegSh
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R-2R attenuator PCB layout question
Just discovered that Mouser does not stock 1206 SMD Susumu resistors which I had in mind while making the PCB layout. May be someone could recommend other good quality not too expensive thin film resistors in 1206 size?

I can change the pads for 0805 and be done with it but I would prefer the 1206 parts if possible since they are slightly easier to solder.
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Old 12th January 2015, 06:10 PM   #12
maxw is offline maxw  United Kingdom
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Panasonic usually have a good range. Just go to the category and search for thin-film and 1206 and see what's available. It can be difficult to get all the values in one range. I think I also ordered from RS components once or twice as well as Mouser and Farnell. Shop by availability, price, specs and don't believe the "X brand sounds great" type of opinions
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Old 12th January 2015, 06:58 PM   #13
OlegSh is offline OlegSh
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R-2R attenuator PCB layout question
Thanks for the hint maxw!
Just checked at Mouser and RS components and only few different values of thin film 1206 0.5~1% resistors are available while in 0805 way more values are there... This time I looked at several manufacturers at once. It also seems that thin film resistors are not so popular as most of stock is thick film and other types... Also what is the difference between metal film and other "film" types in terms of parameters relevant for audio? In principle I am not looking for something fancy here, just good quality not too noisy for audio purposes.
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Old 13th January 2015, 02:18 PM   #14
jackinnj is offline jackinnj  United States
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R-2R attenuator PCB layout question
According to some DIYAUDIO correspondents, SMD resistors can be somewhat non-linear at audio frequencies. Thermal modulation. You might want to get some samples and check for this before committing to a PCB design. CMF55 through-hole devices would work without requiring a lot more real-estate.
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Old 13th January 2015, 04:49 PM   #15
OlegSh is offline OlegSh
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R-2R attenuator PCB layout question
Thanks for the suggestion. But my naive guess is that SMD parts if chosen right can be as good in terms of thermal stability as the through-hole ones since the materials available for both types should be similar.

Anyways, the PCB size is not a concern here. It's just the layout is much cleaner with SMDs and signal pass can be made very short and straight.

Below is the current PCB version. I finally changed the pads for 0805 resistors.
Now is the time for a small relay driver board to place between the arduino and the attenuator. As I understood the ULN2003A driver is 7 channels only. Will look for an 8 channel alternative.
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File Type: png Attenuator0805.png (106.5 KB, 545 views)
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Old 13th January 2015, 04:52 PM   #16
maxw is offline maxw  United Kingdom
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ULN2803A
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Old 13th January 2015, 05:08 PM   #17
OlegSh is offline OlegSh
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R-2R attenuator PCB layout question
Thanks! Exactly what I need. While looking at the ULN2803A I realized that I probably have to reroute the relay coils connection since I assumed the high side switching while the drivers are seems to be designed for low side switching...
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Old 13th January 2015, 08:12 PM   #18
OlegSh is offline OlegSh
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R-2R attenuator PCB layout question
maxw, which I2C port expander have you used? I looked at several but most have rather strange pins configuration. The ones you used seems to have the parallel ports on one side which simplifies the routing...
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Old 13th January 2015, 08:14 PM   #19
maxw is offline maxw  United Kingdom
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I used a MCP23008-E/SO. I have Arduino code for it if you want too.
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Old 13th January 2015, 08:15 PM   #20
OlegSh is offline OlegSh
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R-2R attenuator PCB layout question
just found it in your thread... should have looked there first:-)
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