digital attenuator

[Kerry]

Not sure about the resistors, but they look like thick film SMD with 2512 size similar to this CRCW251210R0FKEG. Will likely want higher precision. The relay is g6sk-2f-dc12 (digikey has these in stock).

[ujamerstand]

Link to the BOM:

here

It's hard to find all the resistor values from the same manufacturer. I also couldn't find 2 values in the appropriate package or in small quantities. Manufacturers are mixed and matched right now, but all of them are ±100ppm/°C, 1% 1W thick film resistors. Also need the value for the compensation caps. If anyone wants to edit or have it in a excel file let me know.

[luvdunhill]

There aren't any compensation caps. You want the bypass caps to be .1uF ceramic, probably np0/c0g.

[Kerry]

Link to the BOM:

here

It's hard to find all the resistor values from the same manufacturer. I also couldn't find 2 values in the appropriate package or in small quantities. Manufacturers are mixed and matched right now, but all of them are ±100ppm/°C, 1% 1W thick film resistors. Also need the value for the compensation caps. If anyone wants to edit or have it in a excel file let me know.

Thanks. I made a couple of small changes added the caps and sent this out for a quote. I think the PCF8574 and the ULN2803 should either both be the A version or not.

There aren't any compensation caps. You want the bypass caps to be .1uF ceramic, probably np0/c0g.

The original boards showed the .1uF caps but not the SMD version.

Kevin - did you want to add these back in.

Also, if it is difficult to get the right resistor values in the 2512 package, we might want to consider using a different sized package, like 1206.

[guzziguy]

Kerry, could you please sign me up for 2 boards either bare or assembled.

[Pars]

I'd take 2 bare. Might be interested in the relays if someone does a group buy on those as well.

[kevin gilmore]

i'm pretty sure i can do a 1206 inside the 2512 package, will look later.

Compensation caps really not necesssary, the uln chips are just transistors

anyway, and really don't need them, and for the other chips, its very close

to the electrolytic anyway. May be able to add a cap on the bottom.

Edited April 14, 2011 by kevin gilmore

[Kerry]

Did someone have suggestions for the resistors (2512 or 1206)? They should be thick film.

Edited.

Edited April 14, 2011 by Kerry

[Kerry]

So I think this baby deserves a name. Any thoughts?

Edited April 14, 2011 by Kerry

[El_Doug]

So I think this baby deserves a name. Any thoughts?

Would calling it "The Umbra" upset Ray?

[digger945]

Dynastep

[Kerry]

OK. I got the quote back from PCBNet (Imagineering) and I think the pricing looks pretty good.

The boards (4 layer) with electrical testing will be $9/board or a bit less depending on qty (based on 80).

The Assembly will be $22/board or a bit less depending on qty (based on 70).

The cost of parts will likely be between $50 and $70 per board depending on where we end up with part selection. I think we can lock the BOM up by early next week.

The thing to consider here since we are getting assembled boards is that they have a fallout rate (defects) of about 1% - 3% on the finished boards, so we may want to order a few extra. I think it is easy to include that in the overall price and it will only move the total per board by about $4 (for three extra boards).

If more are defective, then it is a bigger issue. I'll need to see what the warranty is from PCBNet, but it will minimally cost more in parts. If they all work we will end up with some extras. I might suggest to send them off to Kevin for all of his hard work.

This is my best guess on how to handle possible defects.

Turnaround time will be around a month, but only because we will run a test board first and will have it assembled it to make sure the board / assembly works before the final board run. This will add about $3/board.

This will put the assembled boards roughly between $88 and $108 for quantities of approximately 70 assembled. There will of course be shipping on top of this.

[Driftwood]

Thanks for doing the legwork on this. Are you planning on ordering both assembled and unpopulated boards?

[Kerry]

Yes. We will effectively order a certain number of boards and have a percentage of them assembled.

[n3rdling]

Sounds good

[ujamerstand]

Price looks good. BTW, what's the input impedance of the KGITSOJC circuit?

[luvdunhill]

Price looks good. BTW, what's the input impedance of the KGITSOJC circuit?

Perhaps the better question is what is the output impedance range of the attenuator. Regardless, should be fine looks like a good implementation.

[manaox2]

Glad to see this is coming together. Thank you Kevin and Kerry, this hopefully helps close a large gap and could be exactly what I've been waiting for.

Edited April 15, 2011 by manaox2

[Kerry]

PLEASE SEE POST FOR THE LATEST COUNTS.

Here's the updated list:

EDIT:

I've modified this so if people want both assembled and bare boards they can.

Name - Assembled - Bare Boards

grawk - 4 - 0

Driftwood - 4 - 2

luvdunhill - 0 - 2

ujamerstand - 4 - 0

deepak - 2 - 0

cetoole - 0 - 10

manaox2 - 2 - 0

el_doug - 2 - 0

DouglasQuaid - 2 - 2

jgazal - 2 - 0

Lil Knight - 4 - 0

nattonrice - 0 - 4

kevin gilmore - 4 - 0

looser101 - 4 - 0

chinsettawong - 2 - 0

Kerry - 2 - 4

Fing - 4 - 0

blubliss - 4 - 0

n3rdling - 4 - 0

guzziguy - 2 - 0

Pars - 0 - 2

Nebby - 4 - 0

Flyingsparks - 0 - 4

morphsci - 4 - 0

dwhat - 4 - 0

minivan - 2 - 0

Craig Sawyers - 2 - 4

MASantos - 2 - 0

Vortex - 0 - 10

TOTAL - 70 - 44

Again, if anyone is interested please PM me and I'll add you to the list.

Edited April 19, 2011 by Kerry

[grawk]

Yup, thanks a lot!

[MASantos]

What is being planned to control the attenuator? Will there be any programing involved by the "end user"? Or will it be possible to use a pot like in similar attenuators?

[justin]

What is being planned to control the attenuator? Will there be any programing involved by the "end user"? Or will it be possible to use a pot like in similar attenuators?

you have to touch together 2 bare wires to make a change in volume

[MASantos]

you have to touch together 2 bare wires to make a change in volume

That's easy but no so practical, the easiest would be a pot wired to the board controling the relays.

[kevin gilmore]

There will be multiple versions of things that can control this, from the simple to the

very silly. Pretty sure this is 100% code compatible with the linuxworks stuff should

he choose to ever release it. Standalone single chip arduino based thing with rotary

optical encoder being worked on soon. 4dsystems thing being worked on also.

(see picture previously posted, rest of parts to develop the software inbound)

latest version here

http://gilmore.chem.northwestern.edu/attenuatorsmt9.pdf

all signal traces exactly matched for length and differential time distortion

no more than about 50 femtoseconds. (Seriously) And mainly due to the slight

differences in the internal ground planes.

For the massively insane i have a 6 layer version which is absolutely and perfectly

matched for capacitance too. This version should probably be made with multilayer

arlon or similar material.

Edited April 16, 2011 by kevin gilmore

[MASantos]

That's nice!

Kerry, please add me to the list, 2 assembled boards.