Group Buy - Digital Attenuator (Kevin Gilmore)

[sorenb]

14 hours ago, Pars said:

What is in the Dig. Att. Kits?

The boards I have are the first version, so don't use the MAX chips, but I could be interested in the resistors, etc.

 

the actual saving comes from buying resistors in quantities of 100 ... so we can limit the 'kit' to resistors, no prob

[mypasswordis]

Speaking of the first version, sorry if this has been mentioned before but how did you guys change the I2C address pins for balanced operation? I believe all three address pins are grounded (L L L) on one PCF8574A per board, and the other one is adjustable with the ID pins? I suppose you could put in a PCF8574 for one, or mangle a PCF8574A pin and attach it to high. I see that the new boards use SPI.

Also a bit obvious but, for anyone who hasn't soldered SMT resistors before, it might be a good idea to order two or three spares for each value just in case. Once you accidentally let one of these things fall to the floor it is very difficult to find. Maybe someone has a better way of finding them, or keeping them from flying off in the first place.

[Pars]

10 hours ago, sorenb said:

the actual saving comes from buying resistors in quantities of 100 ... so we can limit the 'kit' to resistors, no prob

but do you have a BOM available for what it is you are ordering for resistors? This is for a 10K attenuator, or do you have multiple variants in mind? 10K is what I would be interested in.

[sorenb]

1 minute ago, Pars said:

but do you have a BOM available for what it is you are ordering for resistors? This is for a 10K attenuator, or do you have multiple variants in mind? 10K is what I would be interested in.

I got this from 50k BOM from Kerry 

I guess we end up with 10k and 50k variants 

 

 

[b0bb]

10 hours ago, sorenb said:

I got this from 50k BOM from Kerry 

I guess we end up with 10k and 50k variants 

 

 

Soren,

Is there a GB for the resistors or resistor kits?

I would be interested in the 50K and 10K sets.

[sorenb]

1 hour ago, b0bb said:

Soren,

Is there a GB for the resistors or resistor kits?

I would be interested in the 50K and 10K sets.

There are a probing going on here , we need more than 25 sets to make this fly

[wokstarr26]

Hi Soren

Cannot change cell in spreadsheet to YES for combine kit.

[sorenb]

2 hours ago, wokstarr26 said:

Hi Soren

Cannot change cell in spreadsheet to YES for combine kit.

done

[DHTGUY]

I want to put together a spreadsheet to check the attenuator values. I have replicated figures from Kerry, 

 For 0.5dB attenuation

The voltage ratio K = Vin / Vout (L attenuator) for 0.5dB = 10 to the power -0.5/20 = 1,0593

For Z = 50k , R Series is 2797 Ohm, (50.000 x (K-1)/K  R Parallel is 843829 (50.000 x 1/(K-1)  (These values match Kerry's and also several web sites)

Now taking these two values 

V Out / V in = Rpar / (Rpar+Rser) = 1,0033 

dB attenuation is 20 x Log10 (1.0033) = -0,03

Where is the mistake? 

 

[sorenb]

those "-" tends to be rather important ...I got -0,50001 dB using your numbers

[b0bb]

12 hours ago, sorenb said:

There are a probing going on here , we need more than 25 sets to make this fly

OK.

Thanks

[mypasswordis]

On 3/6/2016 at 1:53 PM, mypasswordis said:

Speaking of the first version, sorry if this has been mentioned before but how did you guys change the I2C address pins for balanced operation? I believe all three address pins are grounded (L L L) on one PCF8574A per board, and the other one is adjustable with the ID pins? I suppose you could put in a PCF8574 for one, or mangle a PCF8574A pin and attach it to high. I see that the new boards use SPI.

Nvm, I just ran an i2c address scan and figured out the address situation. Got the code working on each attenuator board with a cloud-connected MCU which uses the 4D systems touchscreen LCD KG and Max are using as the input. 256 pixels for 256 settings, just like they wanted it, and +- buttons for fine control because these resistive touchscreens aren't very precise. I will write the code for balanced operation in the weekend, and I ordered some I2C ADC breakout boards for temperature sensors as well. Eventually the goal is to write an Android app for remote control; that way my lazy ass never has to leave the couch.

[Kerry]

I'm writing some arduino based code that supports the original boards as well as the new generation. I also have code for a small oled display as well.

I'd like to like at some raspberry pi based code as well which would give some nice interface options including Bluetooth on the pi 3.

I'm traveling (Birmingham, UK) at the moment but could post the current rev of the code I have once I get back.

[mypasswordis]

Awesome, it would be nice to compare notes.  I won't be getting the ADC boards for awhile anyway. Good idea, rp3 might be the best option for something universal for people to use,  instead of all these different arduino/mcu options and the built in wifi and Bluetooth is nice. 

[kevin gilmore]

a web page accessable by any device is what i really want.  

android or ios specific seems way too much work.

then the touchscreen for those moments when you have to get out of the couch.

[Kerry]

I was thinking it should have a web interface and possibly a universal app to remote control it.

I'm thinking with the pi it could read from dlna music servers if people would want to embed a DAC.

[mypasswordis]

Balanced is a go. I'll work on a channel balance slider next weekend... maybe try to solder up a level shifter and scaler for the ADC. Anyone have recommendations for such a schematic to convert up to +-20v input signal to 0-3v3 input for ADC?

The digital ps i protoboarded is the same (other than different capacitance values) as the one on the dynahi, so 7812, 7805, and murata 3v3. 

[kevin gilmore]

http://gilmore.chem.northwestern.edu/stepattenuator2.jpg

fuck that's tiny 

 

Edited March 14, 2016 by kevin gilmore

[Kerry]

Well stated!

It really helps to use solder paste and a heat gun.  I did all of the resistors and low profile parts then I place the relays and then use a straight edge to get them perfect.

You can solder with an iron but it takes a lot longer.

[mypasswordis]

Way smaller than the first version boards, for sure! Thanks, Kerry and KG, for making this happen. I bought a rework station so things will hopefully go a lot easier than with the previous boards.

I just finished the channel balance code, which parallels that of volume. A slider with a range of 256, so up to 128 on either end, and added +- buttons for fine control. Will investigate what's new with Android SDK in the weekend.

I did some research on the RPi3 after you guys mentioned it, and saw they sell a companion 7" touchscreen for $60!! 7" is a bit unwieldy to put in an amp or DAC, though. What a time to be alive.

[sorenb]

The 10k Dig.Att.kit based on the amb.org:

The kit contains, all resistors (Panasonic ERA's), capacitors and the MAX4820EUP's.

Please transfer your payment to xxx, put your head-case ID into the notes field + "Dig.Att.Kit". As soon as everybody has made their transfer I'll go ahead and order.

Edited May 1, 2019 by sorenb

[Contango]

17 hours ago, sorenb said:

The 10k Dig.Att.kit based on the amb.org:

The kit contains, all resistors (Panasonic ERA's), capacitors and the MAX4820EUP's.

Please transfer your payment to [email protected], put your head-case ID into the notes field + "Dig.Att.Kit". As soon as everybody has made their transfer I'll go ahead and order.

If I'm wrong, can someone please correct me?

This calculator is used for calculating unbalanced attenuator. By adding a balanced leg to the attenuator circuit (and additional resistors into that leg), should not the resistor values be R/2? Otherwise, will not the balanced attenuator board, calculated above as an unbalanced circuit, become a 20K attenuator due to (+RT) + (-RT) = 2*RT? (+RT) and (-RT) being the balanced leg terminators of the circuit. (10.2K + 10.2K = 20.4K)

Soren, Thanks for putting this GB together. I'm looking forward to getting my boards. Now, just to figure out the resistors.

[kevin gilmore]

the balanced version is what is shown times 2.

so the balanced input impedance would be 20k.

[Aive]

Hey Soren, just checking on the update of my 'order' - noticed you've shipped a few already

Thanks.

[sorenb]

25 minutes ago, Aive said:

Hey Soren, just checking on the update of my 'order' - noticed you've shipped a few already

Thanks.

The distribution happens from two locations, US and Denmark, Europe.
Some has been shipped are for people in US ordering LSK389 and/or Dig.Att. boards and no ( Dig.Kit and/or über Group Buy boards).
The Über Group Buy boards has arrived in US, and will probably go out during the weekend.

The non-US part is on its way to Denmark. 

Über Group Buy will start ship next week.
Dig.Kit for US will also ship next week.

/S