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Cheap/simple relay/resistors attenuator for RPI
Cheap/simple relay/resistors attenuator for RPI
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Old 2nd November 2016, 12:01 PM   #1
cdsgames is offline cdsgames  Canada
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Join Date: Jun 2015
Default Cheap/simple relay/resistors attenuator for RPI

Hi ,

we are developing a new shield for RPI that can work either as a stand alone or to be used with allo products (DACs)
We expect them to cost less than 65$

We are using thin film resistors 0.1%

I have attached the preliminary placement.
Attached Files
File Type: pdf Relay attenuator_preliminary placement.pdf (37.0 KB, 211 views)
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Old 2nd November 2016, 01:14 PM   #2
AndrewT is offline AndrewT  Scotland
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new shield?
RPI?
allo?

Talk english, please.
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regards Andrew T.
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Old 2nd November 2016, 01:22 PM   #3
cdsgames is offline cdsgames  Canada
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Basically its a board that plugs on top of Raspberry PI . The board will be compatible with allo.com DACs or can be used as a stand alone 2x RCA in , 2xRCA out
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Old 2nd November 2016, 08:03 PM   #4
OlegSh is offline OlegSh
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Cheap/simple relay/resistors attenuator for RPI
Looks interesting. I would probably skip one relay, 32 attenuation steps is probably enough, IMO. My laptop gets away with only 17 steps and it feels enough. My own R-2R attenuator has 64 steps but I am now thinking to reduce it to 32. You may also wish to reduce the onboard capacitor bank. It may create significant inrush current for RPI at start. I use a single 100uF capacitor next to the relay controller and with 7 relays total (6 for attenuation + mute) I do not have problems. Which relays do you plan to use? The least current hungry ones are not the smallest as far as I know. The small Omron G6K series would require ~20mA per relay when engaged so in your configuration it will result in ~120 mA max current (when all relays are ON). I could not quickly find the specs for RPI power capability through its pins but I would check if 120 mA is not stressing the RPI too much. Also what is the reason for a second I2C expander?

Regards,
Oleg
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Old 3rd November 2016, 11:35 AM   #5
cdsgames is offline cdsgames  Canada
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Hi ,

yes we plan on using the Omron Gk6 relays , the RPI can easily source 1A

Why do you use mute relay...there is enough attenuation with resistors..




Quote:
Originally Posted by OlegSh View Post
Looks interesting. I would probably skip one relay, 32 attenuation steps is probably enough, IMO. My laptop gets away with only 17 steps and it feels enough. My own R-2R attenuator has 64 steps but I am now thinking to reduce it to 32. You may also wish to reduce the onboard capacitor bank. It may create significant inrush current for RPI at start. I use a single 100uF capacitor next to the relay controller and with 7 relays total (6 for attenuation + mute) I do not have problems. Which relays do you plan to use? The least current hungry ones are not the smallest as far as I know. The small Omron G6K series would require ~20mA per relay when engaged so in your configuration it will result in ~120 mA max current (when all relays are ON). I could not quickly find the specs for RPI power capability through its pins but I would check if 120 mA is not stressing the RPI too much. Also what is the reason for a second I2C expander?

Regards,
Oleg
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Old 3rd November 2016, 11:46 AM   #6
OlegSh is offline OlegSh
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Cheap/simple relay/resistors attenuator for RPI
Quote:
Originally Posted by cdsgames View Post
Why do you use mute relay...there is enough attenuation with resistors..
Good question. Some people swear that they need the mute function. I thought I'd rather have it and not need it, than need it and not have it I can always remove the relay and short the pads. But there is an advantage when you need to turn the sound off for a moment and resume with the same level afterwards. There the mute relay comes handy. In my system mute is the default standby state. In your case it is probably easier to engage the mute on the digital side, so no mute relay is needed.
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Old 15th December 2016, 01:14 PM   #7
cdsgames is offline cdsgames  Canada
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PCB received we are assembling. 10k pot , 64 steps + mute.
Attached Files
File Type: pdf Relay Attenuator TOP.pdf (625.6 KB, 118 views)
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Old 19th December 2016, 09:02 AM   #8
cdsgames is offline cdsgames  Canada
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Default board done

We are writing the driver and testing..
Attached Files
File Type: pdf Relay Attenuator (003).pdf (770.1 KB, 96 views)
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Old 19th December 2016, 09:08 AM   #9
Dimdim is offline Dimdim  Greece
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Cheap/simple relay/resistors attenuator for RPI
Pretty little board!
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Old 19th December 2016, 10:07 AM   #10
cdsgames is offline cdsgames  Canada
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Thx for your help Dimitris .


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Originally Posted by Dimdim View Post
Pretty little board!
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