Relay Attenuators and Input Selectors

[maxw]

Hi,
I've designed and built an I2C controlled relay based input selector and attenuator for my own preamp project but due to minimum orders for PCB fabrication and parts from suppliers etc I have a few (about 7 of each) PCBs and components spare.

They are both more or less based on the Twisted Pear Darwin and Joshua Tree but use I2C for control and also SMD components. I'm using an Arduino to control them but you could use a PIC/AVR or anything that can do I2C. I prefer Arduino because its so easy for a beginner to add LCD displays, switches, rotary encoders etc. I'm happy to share my arduino code.

Features:
I2C controlled using an MCP23008
The I2C address can be set using small DIP switches
Surface mount components for shortest possible signal path
PCBs are small (100 x 50 mm) and stackable
Should work as single ended or balanced (need to one per channel)
Omron G6K relays - High quality, low power, very compact with gold alloy contacts
The input selector has 5 inputs and 1 output relay for muting to stop preamp pop or thump etc.
The attenuator has 128 steps + mute.


The input selector is £35 complete.

The attenuator is £35 (not including resistors).
I can supply a set of resistors (10ppm/°C 0.1% thin film 1206) from Rhopoint for £14. You can also use mini melf (MMA) Size 0204.

Any Questions just ask

Schematics:
Input Selector
Attenuator

Pics:

[superR]

Looks very nice. I am currently working on a similar project but I need to start PCB'ing soon. I have a couple of questions;
Do you experience problems with tying the source-gnd's together?
Why do you have 100k between l/r channel and gnd?
What connectors are the blue ones? I am looking for similar ones, but the "wire tools" are very expensive.

[maxw]

Originally Posted by superR

Looks very nice. I am currently working on a similar project but I need to start PCB'ing soon. I have a couple of questions;
Do you experience problems with tying the source-gnd's together?

Thanks!
You mean left and right ground? No problems with my equipment although I've seen some other designs they are separate. What is the point having the separate unless you have completely dual mono system? I'm not sure..

Originally Posted by superR

Why do you have 100k between l/r channel and gnd?

The resistors are optional and are for some fussy equipment that doesn't not like to be left floating when not selected. I've read it can cause a pop/crack when selecting a source like this but I've never personally had this problem.

Originally Posted by superR

What connectors are the blue ones? I am looking for similar ones, but the "wire tools" are very expensive.

They are for the power and the I2C control. I got them from farnel and can dig out the part numbers if you wish!

[superR]

"I got them from farnel and can dig out the part numbers if you wish!"
If you would, that would be great

[maxw]

Originally Posted by superR

"I got them from farnel and can dig out the part numbers if you wish!"
If you would, that would be great

Here you go:
TYCO ELECTRONICS / AMP|281698-4|HEADER, RIGHT ANGLE, 1ROW, 4WAY | Farnell United Kingdom
TYCO ELECTRONICS / AMP|281838-4|CRIMP HOUSING, 1 ROW, 4WAY | Farnell United Kingdom

They are quite good, nice solid connection.

[superR]

And you have used a 200 GBP crimp tool to get the wires on the Crimp sockets?

[maxw]

Originally Posted by superR

And you have used a 200 GBP crimp tool to get the wires on the Crimp sockets?

Haha no I just used £3 pliers. You can use regular headers on the blue sockets too.

[TheShaman]

I've recently bought a similar kit from Max and I'm 100% satisfied.
I have no trouble using my multimeter to identify the resistors nor cut the PCBs.
It was clear to me this was not a fully working "commercial" product but rather an offer from a fellow diy-er who wanted to get rid of some excess parts and PCBs. I thought it'd be a good chance to fool around with Arduino a bit.

Just my 2 cents.

[SY]

I have removed several rules-breaking posts and quite a lot of discussion about a personal dispute. Please handle these matters via email.