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Passive Preamp: Arduino based, remote control, Relay R2R, input selection
Passive Preamp: Arduino based, remote control, Relay R2R, input selection
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Old 23rd July 2015, 06:38 PM   #21
linuxworks is offline linuxworks  United States
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well, I guess I also had to do a passive attenuator, as well (lol):

Click the image to open in full size.

mostly just as a demo. I still prefer buffering but buffering adds dual rail power supply and other build complications. so, yeah, passive is a lot easier to build (lol).

using my delta-1 relay atten, an arduino nano running a modified version of lcduino/volumaster, an adafruit LED display and a rotary encoder.
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Old 10th September 2016, 08:30 AM   #22
RS232 is offline RS232  United Kingdom
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Default MCP23S17 + ULN2803

Hi MaxW
I know this is over a year but I need some clarification...
In the R2R relay board you use the MCP23S17 and 2 ULN2803 and I wander why.
Is it really necessary to have 2 ULNs to drive the realays ?

Ric
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Old 11th September 2016, 07:47 PM   #23
maxw is offline maxw  United Kingdom
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Passive Preamp: Arduino based, remote control, Relay R2R, input selection
Quote:
Originally Posted by RS232 View Post
Hi MaxW
I know this is over a year but I need some clarification...
In the R2R relay board you use the MCP23S17 and 2 ULN2803 and I wander why.
Is it really necessary to have 2 ULNs to drive the realays ?

Ric
Yeah because a MCP23S17 can only sink or source 25mA per pin. If you had relays smaller than that then it would be OK but then you would also need protection diodes too though (these are inside the ULN2803).
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Old 12th September 2016, 12:09 AM   #24
RS232 is offline RS232  United Kingdom
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Hi
Thanks for the answer but I'm still a bit confused.
I read the datasheets for the MCP23X17 and for the the ULN2803
The 25mA from the MCP23S17 are enough to drive the ULN2803 and this one can supply 500mA in each pin and I think is more then enough to drive the small relays, I'm using Telecom relays from Nec and they only need around 160ma to latch and hold the contact.
My question was about this case if the ULN2803 can supply 500mA/pin why did you use 2 of them to drive the 8 relays (2xULN2803 are 16 drivers)
Sorry to be a pain but I like to understand the reason behind this

Ric
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Old 12th September 2016, 04:32 AM   #25
maxw is offline maxw  United Kingdom
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Passive Preamp: Arduino based, remote control, Relay R2R, input selection
Quote:
Originally Posted by RS232 View Post
Hi
My question was about this case if the ULN2803 can supply 500mA/pin why did you use 2 of them to drive the 8 relays (2xULN2803 are 16 drivers)
Ah now I understand your question. The reason is that I am using latching (or bi-stable) relays.

Some info here:
Switch Types and Common Terminology - National Instruments

That means I need to be able to give the relay coil 5V-0V and also 0V-5V. One to set the relay one way and one to set it the other way. For this reason I need to use two I/O pins per relay and I pulse these I/O pins +/- to set it one way and then -/+ to the other way.

Make sense?
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Old 12th September 2016, 02:33 PM   #26
linuxworks is offline linuxworks  United States
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visit the amb forum and search on lcduinoand delta1. max used that system and even some of my code too, iirc.

(I was the developer of those systems.)
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Old 12th September 2016, 10:05 PM   #27
RS232 is offline RS232  United Kingdom
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Hi maxw
Yes that make sense, never thought the relays were latching ones...
Like me I'm using the Nec ones because I have dozens of them, they are 4.5V ones but with silver with gold coating contacts I can't go wrong.
Linuxworks thanks will have a look.

Ric
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Old 28th September 2016, 01:32 AM   #28
rainwalk is offline rainwalk  South Korea
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Default Encoder connection

Hi Maxw,
As I told you before by email, now I'm building up your passive preamp as an relay R2R volume controller in my preamp.

As you guess, last night i tried to upload the code into arduino and connect the passive preamp PCB, but noting happen. The led light well. but when I turned to encoder there are noting happen. No clicking sound from preamp board.

I thought I never tried arduino, so that tere are some mis-operation... ex/ libraries, how to install..

for more quick check, would you let me know how to connect the encoder?
In you diagram, there are 4 lines from encoder. My one have 5 pin. up-side pin are 3. low-side pin are 2.

would you let me know or attache more detail picture??
Thanks you.
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Old 29th September 2016, 11:32 AM   #29
RS232 is offline RS232  United Kingdom
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I also need some help but with something else.
To rainwalk, the 2 pins are the build in switch and the other 3 ones are channel A/B and 5V common.
I'm doing this volume control (just the relays for volume) and I had to call the "wire" library to control the MCPxxxxx but I'm using I2C protocol.
To Maxw, need a little help with the resistor for the relays can you help ( pleaseee ) ?

Ric
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Old 30th September 2016, 01:03 PM   #30
RS232 is offline RS232  United Kingdom
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Please help maxw...
I can't get my head around your volume relays resistors, I have looked online lots of r2r ladder calculators and none gives me the same values that you have in your bom.
From what I can see yours is a 10k attenuator (am I wrong ?) every time I try one of the online calculator I get different values.
Can you give me a hand please...
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